From cf68fffb66d60d96209446bfc4a15291dc5a5d41 Mon Sep 17 00:00:00 2001
From: Sami Tolvanen <samitolvanen@google.com>
Date: Thu, 8 Apr 2021 11:28:26 -0700
Subject: add support for Clang CFI
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

This change adds support for Clang’s forward-edge Control Flow
Integrity (CFI) checking. With CONFIG_CFI_CLANG, the compiler
injects a runtime check before each indirect function call to ensure
the target is a valid function with the correct static type. This
restricts possible call targets and makes it more difficult for
an attacker to exploit bugs that allow the modification of stored
function pointers. For more details, see:

  https://clang.llvm.org/docs/ControlFlowIntegrity.html

Clang requires CONFIG_LTO_CLANG to be enabled with CFI to gain
visibility to possible call targets. Kernel modules are supported
with Clang’s cross-DSO CFI mode, which allows checking between
independently compiled components.

With CFI enabled, the compiler injects a __cfi_check() function into
the kernel and each module for validating local call targets. For
cross-module calls that cannot be validated locally, the compiler
calls the global __cfi_slowpath_diag() function, which determines
the target module and calls the correct __cfi_check() function. This
patch includes a slowpath implementation that uses __module_address()
to resolve call targets, and with CONFIG_CFI_CLANG_SHADOW enabled, a
shadow map that speeds up module look-ups by ~3x.

Clang implements indirect call checking using jump tables and
offers two methods of generating them. With canonical jump tables,
the compiler renames each address-taken function to <function>.cfi
and points the original symbol to a jump table entry, which passes
__cfi_check() validation. This isn’t compatible with stand-alone
assembly code, which the compiler doesn’t instrument, and would
result in indirect calls to assembly code to fail. Therefore, we
default to using non-canonical jump tables instead, where the compiler
generates a local jump table entry <function>.cfi_jt for each
address-taken function, and replaces all references to the function
with the address of the jump table entry.

Note that because non-canonical jump table addresses are local
to each component, they break cross-module function address
equality. Specifically, the address of a global function will be
different in each module, as it's replaced with the address of a local
jump table entry. If this address is passed to a different module,
it won’t match the address of the same function taken there. This
may break code that relies on comparing addresses passed from other
components.

CFI checking can be disabled in a function with the __nocfi attribute.
Additionally, CFI can be disabled for an entire compilation unit by
filtering out CC_FLAGS_CFI.

By default, CFI failures result in a kernel panic to stop a potential
exploit. CONFIG_CFI_PERMISSIVE enables a permissive mode, where the
kernel prints out a rate-limited warning instead, and allows execution
to continue. This option is helpful for locating type mismatches, but
should only be enabled during development.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210408182843.1754385-2-samitolvanen@google.com
---
 include/linux/cfi.h            | 41 +++++++++++++++++++++++++++++++++++++++++
 include/linux/compiler-clang.h |  2 ++
 include/linux/compiler_types.h |  4 ++++
 include/linux/init.h           |  2 +-
 include/linux/module.h         | 13 +++++++++++--
 5 files changed, 59 insertions(+), 3 deletions(-)
 create mode 100644 include/linux/cfi.h

(limited to 'include/linux')

diff --git a/include/linux/cfi.h b/include/linux/cfi.h
new file mode 100644
index 000000000000..879744aaa6e0
--- /dev/null
+++ b/include/linux/cfi.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Clang Control Flow Integrity (CFI) support.
+ *
+ * Copyright (C) 2021 Google LLC
+ */
+#ifndef _LINUX_CFI_H
+#define _LINUX_CFI_H
+
+#ifdef CONFIG_CFI_CLANG
+typedef void (*cfi_check_fn)(uint64_t id, void *ptr, void *diag);
+
+/* Compiler-generated function in each module, and the kernel */
+extern void __cfi_check(uint64_t id, void *ptr, void *diag);
+
+/*
+ * Force the compiler to generate a CFI jump table entry for a function
+ * and store the jump table address to __cfi_jt_<function>.
+ */
+#define __CFI_ADDRESSABLE(fn, __attr) \
+	const void *__cfi_jt_ ## fn __visible __attr = (void *)&fn
+
+#ifdef CONFIG_CFI_CLANG_SHADOW
+
+extern void cfi_module_add(struct module *mod, unsigned long base_addr);
+extern void cfi_module_remove(struct module *mod, unsigned long base_addr);
+
+#else
+
+static inline void cfi_module_add(struct module *mod, unsigned long base_addr) {}
+static inline void cfi_module_remove(struct module *mod, unsigned long base_addr) {}
+
+#endif /* CONFIG_CFI_CLANG_SHADOW */
+
+#else /* !CONFIG_CFI_CLANG */
+
+#define __CFI_ADDRESSABLE(fn, __attr)
+
+#endif /* CONFIG_CFI_CLANG */
+
+#endif /* _LINUX_CFI_H */
diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index d217c382b02d..6de9d0c9377e 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -61,3 +61,5 @@
 #if __has_feature(shadow_call_stack)
 # define __noscs	__attribute__((__no_sanitize__("shadow-call-stack")))
 #endif
+
+#define __nocfi		__attribute__((__no_sanitize__("cfi")))
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index e5dd5a4ae946..796935a37e37 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -242,6 +242,10 @@ struct ftrace_likely_data {
 # define __noscs
 #endif
 
+#ifndef __nocfi
+# define __nocfi
+#endif
+
 #ifndef asm_volatile_goto
 #define asm_volatile_goto(x...) asm goto(x)
 #endif
diff --git a/include/linux/init.h b/include/linux/init.h
index 31f54de58429..b3ea15348fbd 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -47,7 +47,7 @@
 
 /* These are for everybody (although not all archs will actually
    discard it in modules) */
-#define __init		__section(".init.text") __cold  __latent_entropy __noinitretpoline
+#define __init		__section(".init.text") __cold  __latent_entropy __noinitretpoline __nocfi
 #define __initdata	__section(".init.data")
 #define __initconst	__section(".init.rodata")
 #define __exitdata	__section(".exit.data")
diff --git a/include/linux/module.h b/include/linux/module.h
index da4b6fbe8ebe..8100bb477d86 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -26,6 +26,7 @@
 #include <linux/tracepoint-defs.h>
 #include <linux/srcu.h>
 #include <linux/static_call_types.h>
+#include <linux/cfi.h>
 
 #include <linux/percpu.h>
 #include <asm/module.h>
@@ -128,13 +129,17 @@ extern void cleanup_module(void);
 #define module_init(initfn)					\
 	static inline initcall_t __maybe_unused __inittest(void)		\
 	{ return initfn; }					\
-	int init_module(void) __copy(initfn) __attribute__((alias(#initfn)));
+	int init_module(void) __copy(initfn)			\
+		__attribute__((alias(#initfn)));		\
+	__CFI_ADDRESSABLE(init_module, __initdata);
 
 /* This is only required if you want to be unloadable. */
 #define module_exit(exitfn)					\
 	static inline exitcall_t __maybe_unused __exittest(void)		\
 	{ return exitfn; }					\
-	void cleanup_module(void) __copy(exitfn) __attribute__((alias(#exitfn)));
+	void cleanup_module(void) __copy(exitfn)		\
+		__attribute__((alias(#exitfn)));		\
+	__CFI_ADDRESSABLE(cleanup_module, __exitdata);
 
 #endif
 
@@ -376,6 +381,10 @@ struct module {
 	const s32 *crcs;
 	unsigned int num_syms;
 
+#ifdef CONFIG_CFI_CLANG
+	cfi_check_fn cfi_check;
+#endif
+
 	/* Kernel parameters. */
 #ifdef CONFIG_SYSFS
 	struct mutex param_lock;
-- 
cgit 


From ff301ceb5299551c3650d0e07ba879b766da4cc0 Mon Sep 17 00:00:00 2001
From: Sami Tolvanen <samitolvanen@google.com>
Date: Thu, 8 Apr 2021 11:28:27 -0700
Subject: cfi: add __cficanonical

With CONFIG_CFI_CLANG, the compiler replaces a function address taken
in C code with the address of a local jump table entry, which passes
runtime indirect call checks. However, the compiler won't replace
addresses taken in assembly code, which will result in a CFI failure
if we later jump to such an address in instrumented C code. The code
generated for the non-canonical jump table looks this:

  <noncanonical.cfi_jt>: /* In C, &noncanonical points here */
	jmp noncanonical
  ...
  <noncanonical>:        /* function body */
	...

This change adds the __cficanonical attribute, which tells the
compiler to use a canonical jump table for the function instead. This
means the compiler will rename the actual function to <function>.cfi
and points the original symbol to the jump table entry instead:

  <canonical>:           /* jump table entry */
	jmp canonical.cfi
  ...
  <canonical.cfi>:       /* function body */
	...

As a result, the address taken in assembly, or other non-instrumented
code always points to the jump table and therefore, can be used for
indirect calls in instrumented code without tripping CFI checks.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>   # pci.h
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210408182843.1754385-3-samitolvanen@google.com
---
 include/linux/compiler-clang.h | 1 +
 include/linux/compiler_types.h | 4 ++++
 include/linux/init.h           | 4 ++--
 include/linux/pci.h            | 4 ++--
 4 files changed, 9 insertions(+), 4 deletions(-)

(limited to 'include/linux')

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index 6de9d0c9377e..adbe76b203e2 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -63,3 +63,4 @@
 #endif
 
 #define __nocfi		__attribute__((__no_sanitize__("cfi")))
+#define __cficanonical	__attribute__((__cfi_canonical_jump_table__))
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 796935a37e37..d29bda7f6ebd 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -246,6 +246,10 @@ struct ftrace_likely_data {
 # define __nocfi
 #endif
 
+#ifndef __cficanonical
+# define __cficanonical
+#endif
+
 #ifndef asm_volatile_goto
 #define asm_volatile_goto(x...) asm goto(x)
 #endif
diff --git a/include/linux/init.h b/include/linux/init.h
index b3ea15348fbd..045ad1650ed1 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -220,8 +220,8 @@ extern bool initcall_debug;
 	__initcall_name(initstub, __iid, id)
 
 #define __define_initcall_stub(__stub, fn)			\
-	int __init __stub(void);				\
-	int __init __stub(void)					\
+	int __init __cficanonical __stub(void);			\
+	int __init __cficanonical __stub(void)			\
 	{ 							\
 		return fn();					\
 	}							\
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 86c799c97b77..39684b72db91 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1944,8 +1944,8 @@ enum pci_fixup_pass {
 #ifdef CONFIG_LTO_CLANG
 #define __DECLARE_PCI_FIXUP_SECTION(sec, name, vendor, device, class,	\
 				  class_shift, hook, stub)		\
-	void stub(struct pci_dev *dev);					\
-	void stub(struct pci_dev *dev)					\
+	void __cficanonical stub(struct pci_dev *dev);			\
+	void __cficanonical stub(struct pci_dev *dev)			\
 	{ 								\
 		hook(dev); 						\
 	}								\
-- 
cgit 


From 5caf968262df0ec7a3377fb67d4a6bfa979cb028 Mon Sep 17 00:00:00 2001
From: Sami Tolvanen <samitolvanen@google.com>
Date: Thu, 8 Apr 2021 11:28:28 -0700
Subject: mm: add generic function_nocfi macro

With CONFIG_CFI_CLANG, the compiler replaces function addresses
in instrumented C code with jump table addresses. This means that
__pa_symbol(function) returns the physical address of the jump table
entry instead of the actual function, which may not work as the jump
table code will immediately jump to a virtual address that may not be
mapped.

To avoid this address space confusion, this change adds a generic
definition for function_nocfi(), which architectures that support CFI
can override. The typical implementation of would use inline assembly
to take the function address, which avoids compiler instrumentation.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210408182843.1754385-4-samitolvanen@google.com
---
 include/linux/mm.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

(limited to 'include/linux')

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8ba434287387..22cce9c7dd05 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -124,6 +124,16 @@ extern int mmap_rnd_compat_bits __read_mostly;
 #define lm_alias(x)	__va(__pa_symbol(x))
 #endif
 
+/*
+ * With CONFIG_CFI_CLANG, the compiler replaces function addresses in
+ * instrumented C code with jump table addresses. Architectures that
+ * support CFI can define this macro to return the actual function address
+ * when needed.
+ */
+#ifndef function_nocfi
+#define function_nocfi(x) (x)
+#endif
+
 /*
  * To prevent common memory management code establishing
  * a zero page mapping on a read fault.
-- 
cgit 


From 9f5b4009980f369acb80b72235b2d66c3fd6eca6 Mon Sep 17 00:00:00 2001
From: Sami Tolvanen <samitolvanen@google.com>
Date: Thu, 8 Apr 2021 11:28:33 -0700
Subject: bpf: disable CFI in dispatcher functions

BPF dispatcher functions are patched at runtime to perform direct
instead of indirect calls. Disable CFI for the dispatcher functions to
avoid conflicts.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210408182843.1754385-9-samitolvanen@google.com
---
 include/linux/bpf.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

(limited to 'include/linux')

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 3625f019767d..2f46f98479e1 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -650,7 +650,7 @@ struct bpf_dispatcher {
 	struct bpf_ksym ksym;
 };
 
-static __always_inline unsigned int bpf_dispatcher_nop_func(
+static __always_inline __nocfi unsigned int bpf_dispatcher_nop_func(
 	const void *ctx,
 	const struct bpf_insn *insnsi,
 	unsigned int (*bpf_func)(const void *,
@@ -678,7 +678,7 @@ void bpf_trampoline_put(struct bpf_trampoline *tr);
 }
 
 #define DEFINE_BPF_DISPATCHER(name)					\
-	noinline unsigned int bpf_dispatcher_##name##_func(		\
+	noinline __nocfi unsigned int bpf_dispatcher_##name##_func(	\
 		const void *ctx,					\
 		const struct bpf_insn *insnsi,				\
 		unsigned int (*bpf_func)(const void *,			\
-- 
cgit 


From 4f0f586bf0c898233d8f316f471a21db2abd522d Mon Sep 17 00:00:00 2001
From: Sami Tolvanen <samitolvanen@google.com>
Date: Thu, 8 Apr 2021 11:28:34 -0700
Subject: treewide: Change list_sort to use const pointers

list_sort() internally casts the comparison function passed to it
to a different type with constant struct list_head pointers, and
uses this pointer to call the functions, which trips indirect call
Control-Flow Integrity (CFI) checking.

Instead of removing the consts, this change defines the
list_cmp_func_t type and changes the comparison function types of
all list_sort() callers to use const pointers, thus avoiding type
mismatches.

Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210408182843.1754385-10-samitolvanen@google.com
---
 arch/arm64/kvm/vgic/vgic-its.c                         |  8 ++++----
 arch/arm64/kvm/vgic/vgic.c                             |  3 ++-
 block/blk-mq-sched.c                                   |  3 ++-
 block/blk-mq.c                                         |  3 ++-
 drivers/acpi/nfit/core.c                               |  3 ++-
 drivers/acpi/numa/hmat.c                               |  3 ++-
 drivers/clk/keystone/sci-clk.c                         |  4 ++--
 drivers/gpu/drm/drm_modes.c                            |  3 ++-
 drivers/gpu/drm/i915/gt/intel_engine_user.c            |  3 ++-
 drivers/gpu/drm/i915/gvt/debugfs.c                     |  2 +-
 drivers/gpu/drm/i915/selftests/i915_gem_gtt.c          |  3 ++-
 drivers/gpu/drm/radeon/radeon_cs.c                     |  4 ++--
 drivers/infiniband/hw/usnic/usnic_uiom_interval_tree.c |  3 ++-
 drivers/interconnect/qcom/bcm-voter.c                  |  2 +-
 drivers/md/raid5.c                                     |  3 ++-
 drivers/misc/sram.c                                    |  4 ++--
 drivers/nvme/host/core.c                               |  3 ++-
 drivers/pci/controller/cadence/pcie-cadence-host.c     |  3 ++-
 drivers/spi/spi-loopback-test.c                        |  3 ++-
 fs/btrfs/raid56.c                                      |  3 ++-
 fs/btrfs/tree-log.c                                    |  3 ++-
 fs/btrfs/volumes.c                                     |  3 ++-
 fs/ext4/fsmap.c                                        |  4 ++--
 fs/gfs2/glock.c                                        |  3 ++-
 fs/gfs2/log.c                                          |  2 +-
 fs/gfs2/lops.c                                         |  3 ++-
 fs/iomap/buffered-io.c                                 |  3 ++-
 fs/ubifs/gc.c                                          |  7 ++++---
 fs/ubifs/replay.c                                      |  4 ++--
 fs/xfs/scrub/bitmap.c                                  |  4 ++--
 fs/xfs/xfs_bmap_item.c                                 |  4 ++--
 fs/xfs/xfs_buf.c                                       |  6 +++---
 fs/xfs/xfs_extent_busy.c                               |  4 ++--
 fs/xfs/xfs_extent_busy.h                               |  3 ++-
 fs/xfs/xfs_extfree_item.c                              |  4 ++--
 fs/xfs/xfs_refcount_item.c                             |  4 ++--
 fs/xfs/xfs_rmap_item.c                                 |  4 ++--
 include/linux/list_sort.h                              |  7 ++++---
 lib/list_sort.c                                        | 17 ++++++-----------
 lib/test_list_sort.c                                   |  3 ++-
 net/tipc/name_table.c                                  |  4 ++--
 41 files changed, 90 insertions(+), 72 deletions(-)

(limited to 'include/linux')

diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
index 40cbaca81333..b9518f94bd43 100644
--- a/arch/arm64/kvm/vgic/vgic-its.c
+++ b/arch/arm64/kvm/vgic/vgic-its.c
@@ -2190,8 +2190,8 @@ static int vgic_its_restore_ite(struct vgic_its *its, u32 event_id,
 	return offset;
 }
 
-static int vgic_its_ite_cmp(void *priv, struct list_head *a,
-			    struct list_head *b)
+static int vgic_its_ite_cmp(void *priv, const struct list_head *a,
+			    const struct list_head *b)
 {
 	struct its_ite *itea = container_of(a, struct its_ite, ite_list);
 	struct its_ite *iteb = container_of(b, struct its_ite, ite_list);
@@ -2329,8 +2329,8 @@ static int vgic_its_restore_dte(struct vgic_its *its, u32 id,
 	return offset;
 }
 
-static int vgic_its_device_cmp(void *priv, struct list_head *a,
-			       struct list_head *b)
+static int vgic_its_device_cmp(void *priv, const struct list_head *a,
+			       const struct list_head *b)
 {
 	struct its_device *deva = container_of(a, struct its_device, dev_list);
 	struct its_device *devb = container_of(b, struct its_device, dev_list);
diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
index 1c597c9885fa..15b666200f0b 100644
--- a/arch/arm64/kvm/vgic/vgic.c
+++ b/arch/arm64/kvm/vgic/vgic.c
@@ -255,7 +255,8 @@ static struct kvm_vcpu *vgic_target_oracle(struct vgic_irq *irq)
  * Return negative if "a" sorts before "b", 0 to preserve order, and positive
  * to sort "b" before "a".
  */
-static int vgic_irq_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int vgic_irq_cmp(void *priv, const struct list_head *a,
+			const struct list_head *b)
 {
 	struct vgic_irq *irqa = container_of(a, struct vgic_irq, ap_list);
 	struct vgic_irq *irqb = container_of(b, struct vgic_irq, ap_list);
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index e1e997af89a0..3ebd6f10f728 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -75,7 +75,8 @@ void blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
 	blk_mq_run_hw_queue(hctx, true);
 }
 
-static int sched_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int sched_rq_cmp(void *priv, const struct list_head *a,
+			const struct list_head *b)
 {
 	struct request *rqa = container_of(a, struct request, queuelist);
 	struct request *rqb = container_of(b, struct request, queuelist);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index d4d7c1caa439..4e3a70ab5be1 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1895,7 +1895,8 @@ void blk_mq_insert_requests(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx,
 	spin_unlock(&ctx->lock);
 }
 
-static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int plug_rq_cmp(void *priv, const struct list_head *a,
+		       const struct list_head *b)
 {
 	struct request *rqa = container_of(a, struct request, queuelist);
 	struct request *rqb = container_of(b, struct request, queuelist);
diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
index 8c5dde628405..d15e3ee93b5b 100644
--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -1195,7 +1195,8 @@ static int __nfit_mem_init(struct acpi_nfit_desc *acpi_desc,
 	return 0;
 }
 
-static int nfit_mem_cmp(void *priv, struct list_head *_a, struct list_head *_b)
+static int nfit_mem_cmp(void *priv, const struct list_head *_a,
+		const struct list_head *_b)
 {
 	struct nfit_mem *a = container_of(_a, typeof(*a), list);
 	struct nfit_mem *b = container_of(_b, typeof(*b), list);
diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
index cb73a5d6ea76..137a5dd880c2 100644
--- a/drivers/acpi/numa/hmat.c
+++ b/drivers/acpi/numa/hmat.c
@@ -558,7 +558,8 @@ static bool hmat_update_best(u8 type, u32 value, u32 *best)
 	return updated;
 }
 
-static int initiator_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int initiator_cmp(void *priv, const struct list_head *a,
+			 const struct list_head *b)
 {
 	struct memory_initiator *ia;
 	struct memory_initiator *ib;
diff --git a/drivers/clk/keystone/sci-clk.c b/drivers/clk/keystone/sci-clk.c
index aaf31abe1c8f..7e1b136e71ae 100644
--- a/drivers/clk/keystone/sci-clk.c
+++ b/drivers/clk/keystone/sci-clk.c
@@ -503,8 +503,8 @@ static int ti_sci_scan_clocks_from_fw(struct sci_clk_provider *provider)
 
 #else
 
-static int _cmp_sci_clk_list(void *priv, struct list_head *a,
-			     struct list_head *b)
+static int _cmp_sci_clk_list(void *priv, const struct list_head *a,
+			     const struct list_head *b)
 {
 	struct sci_clk *ca = container_of(a, struct sci_clk, node);
 	struct sci_clk *cb = container_of(b, struct sci_clk, node);
diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index 1ac67d4505e0..6662d0457ad6 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -1290,7 +1290,8 @@ EXPORT_SYMBOL(drm_mode_prune_invalid);
  * Negative if @lh_a is better than @lh_b, zero if they're equivalent, or
  * positive if @lh_b is better than @lh_a.
  */
-static int drm_mode_compare(void *priv, struct list_head *lh_a, struct list_head *lh_b)
+static int drm_mode_compare(void *priv, const struct list_head *lh_a,
+			    const struct list_head *lh_b)
 {
 	struct drm_display_mode *a = list_entry(lh_a, struct drm_display_mode, head);
 	struct drm_display_mode *b = list_entry(lh_b, struct drm_display_mode, head);
diff --git a/drivers/gpu/drm/i915/gt/intel_engine_user.c b/drivers/gpu/drm/i915/gt/intel_engine_user.c
index 34e6096f196e..da21d2a10cc9 100644
--- a/drivers/gpu/drm/i915/gt/intel_engine_user.c
+++ b/drivers/gpu/drm/i915/gt/intel_engine_user.c
@@ -49,7 +49,8 @@ static const u8 uabi_classes[] = {
 	[VIDEO_ENHANCEMENT_CLASS] = I915_ENGINE_CLASS_VIDEO_ENHANCE,
 };
 
-static int engine_cmp(void *priv, struct list_head *A, struct list_head *B)
+static int engine_cmp(void *priv, const struct list_head *A,
+		      const struct list_head *B)
 {
 	const struct intel_engine_cs *a =
 		container_of((struct rb_node *)A, typeof(*a), uabi_node);
diff --git a/drivers/gpu/drm/i915/gvt/debugfs.c b/drivers/gpu/drm/i915/gvt/debugfs.c
index 62e6a14ad58e..9f1c209d9251 100644
--- a/drivers/gpu/drm/i915/gvt/debugfs.c
+++ b/drivers/gpu/drm/i915/gvt/debugfs.c
@@ -41,7 +41,7 @@ struct diff_mmio {
 
 /* Compare two diff_mmio items. */
 static int mmio_offset_compare(void *priv,
-	struct list_head *a, struct list_head *b)
+	const struct list_head *a, const struct list_head *b)
 {
 	struct diff_mmio *ma;
 	struct diff_mmio *mb;
diff --git a/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c b/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c
index c1adea8765a9..52b9c39e0155 100644
--- a/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/selftests/i915_gem_gtt.c
@@ -1076,7 +1076,8 @@ static int igt_ppgtt_shrink_boom(void *arg)
 	return exercise_ppgtt(arg, shrink_boom);
 }
 
-static int sort_holes(void *priv, struct list_head *A, struct list_head *B)
+static int sort_holes(void *priv, const struct list_head *A,
+		      const struct list_head *B)
 {
 	struct drm_mm_node *a = list_entry(A, typeof(*a), hole_stack);
 	struct drm_mm_node *b = list_entry(B, typeof(*b), hole_stack);
diff --git a/drivers/gpu/drm/radeon/radeon_cs.c b/drivers/gpu/drm/radeon/radeon_cs.c
index 35e937d39b51..1a5c3db1d53b 100644
--- a/drivers/gpu/drm/radeon/radeon_cs.c
+++ b/drivers/gpu/drm/radeon/radeon_cs.c
@@ -393,8 +393,8 @@ int radeon_cs_parser_init(struct radeon_cs_parser *p, void *data)
 	return 0;
 }
 
-static int cmp_size_smaller_first(void *priv, struct list_head *a,
-				  struct list_head *b)
+static int cmp_size_smaller_first(void *priv, const struct list_head *a,
+				  const struct list_head *b)
 {
 	struct radeon_bo_list *la = list_entry(a, struct radeon_bo_list, tv.head);
 	struct radeon_bo_list *lb = list_entry(b, struct radeon_bo_list, tv.head);
diff --git a/drivers/infiniband/hw/usnic/usnic_uiom_interval_tree.c b/drivers/infiniband/hw/usnic/usnic_uiom_interval_tree.c
index d399523206c7..29d71267af78 100644
--- a/drivers/infiniband/hw/usnic/usnic_uiom_interval_tree.c
+++ b/drivers/infiniband/hw/usnic/usnic_uiom_interval_tree.c
@@ -83,7 +83,8 @@ usnic_uiom_interval_node_alloc(long int start, long int last, int ref_cnt,
 	return interval;
 }
 
-static int interval_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int interval_cmp(void *priv, const struct list_head *a,
+			const struct list_head *b)
 {
 	struct usnic_uiom_interval_node *node_a, *node_b;
 
diff --git a/drivers/interconnect/qcom/bcm-voter.c b/drivers/interconnect/qcom/bcm-voter.c
index 1cc565bce2f4..d1591a28b743 100644
--- a/drivers/interconnect/qcom/bcm-voter.c
+++ b/drivers/interconnect/qcom/bcm-voter.c
@@ -39,7 +39,7 @@ struct bcm_voter {
 	u32 tcs_wait;
 };
 
-static int cmp_vcd(void *priv, struct list_head *a, struct list_head *b)
+static int cmp_vcd(void *priv, const struct list_head *a, const struct list_head *b)
 {
 	const struct qcom_icc_bcm *bcm_a = list_entry(a, struct qcom_icc_bcm, list);
 	const struct qcom_icc_bcm *bcm_b = list_entry(b, struct qcom_icc_bcm, list);
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 5d57a5bd171f..841e1c1aa5e6 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -953,7 +953,8 @@ static void dispatch_bio_list(struct bio_list *tmp)
 		submit_bio_noacct(bio);
 }
 
-static int cmp_stripe(void *priv, struct list_head *a, struct list_head *b)
+static int cmp_stripe(void *priv, const struct list_head *a,
+		      const struct list_head *b)
 {
 	const struct r5pending_data *da = list_entry(a,
 				struct r5pending_data, sibling);
diff --git a/drivers/misc/sram.c b/drivers/misc/sram.c
index 6c1a23cb3e8c..202bf951e909 100644
--- a/drivers/misc/sram.c
+++ b/drivers/misc/sram.c
@@ -144,8 +144,8 @@ static void sram_free_partitions(struct sram_dev *sram)
 	}
 }
 
-static int sram_reserve_cmp(void *priv, struct list_head *a,
-					struct list_head *b)
+static int sram_reserve_cmp(void *priv, const struct list_head *a,
+					const struct list_head *b)
 {
 	struct sram_reserve *ra = list_entry(a, struct sram_reserve, list);
 	struct sram_reserve *rb = list_entry(b, struct sram_reserve, list);
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 0896e21642be..5eaaa51a5e30 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3855,7 +3855,8 @@ out_unlock:
 	return ret;
 }
 
-static int ns_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int ns_cmp(void *priv, const struct list_head *a,
+		const struct list_head *b)
 {
 	struct nvme_ns *nsa = container_of(a, struct nvme_ns, list);
 	struct nvme_ns *nsb = container_of(b, struct nvme_ns, list);
diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c b/drivers/pci/controller/cadence/pcie-cadence-host.c
index 73dcf8cf98fb..ae1c55503513 100644
--- a/drivers/pci/controller/cadence/pcie-cadence-host.c
+++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
@@ -345,7 +345,8 @@ static int cdns_pcie_host_bar_config(struct cdns_pcie_rc *rc,
 	return 0;
 }
 
-static int cdns_pcie_host_dma_ranges_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int cdns_pcie_host_dma_ranges_cmp(void *priv, const struct list_head *a,
+					 const struct list_head *b)
 {
 	struct resource_entry *entry1, *entry2;
 
diff --git a/drivers/spi/spi-loopback-test.c b/drivers/spi/spi-loopback-test.c
index df981e55c24c..f1cf2232f0b5 100644
--- a/drivers/spi/spi-loopback-test.c
+++ b/drivers/spi/spi-loopback-test.c
@@ -454,7 +454,8 @@ struct rx_ranges {
 	u8 *end;
 };
 
-static int rx_ranges_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int rx_ranges_cmp(void *priv, const struct list_head *a,
+			 const struct list_head *b)
 {
 	struct rx_ranges *rx_a = list_entry(a, struct rx_ranges, list);
 	struct rx_ranges *rx_b = list_entry(b, struct rx_ranges, list);
diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
index 8c31357f08ed..f4139de63b2e 100644
--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -1634,7 +1634,8 @@ struct btrfs_plug_cb {
 /*
  * rbios on the plug list are sorted for easier merging.
  */
-static int plug_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int plug_cmp(void *priv, const struct list_head *a,
+		    const struct list_head *b)
 {
 	struct btrfs_raid_bio *ra = container_of(a, struct btrfs_raid_bio,
 						 plug_list);
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 92a368627791..00a88bd8105e 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -4136,7 +4136,8 @@ static noinline int copy_items(struct btrfs_trans_handle *trans,
 	return ret;
 }
 
-static int extent_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int extent_cmp(void *priv, const struct list_head *a,
+		      const struct list_head *b)
 {
 	struct extent_map *em1, *em2;
 
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 1c6810bbaf8b..912dd8b9f156 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1224,7 +1224,8 @@ static int open_fs_devices(struct btrfs_fs_devices *fs_devices,
 	return 0;
 }
 
-static int devid_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int devid_cmp(void *priv, const struct list_head *a,
+		     const struct list_head *b)
 {
 	struct btrfs_device *dev1, *dev2;
 
diff --git a/fs/ext4/fsmap.c b/fs/ext4/fsmap.c
index 4c2a9fe30067..4493ef0c715e 100644
--- a/fs/ext4/fsmap.c
+++ b/fs/ext4/fsmap.c
@@ -354,8 +354,8 @@ static unsigned int ext4_getfsmap_find_sb(struct super_block *sb,
 
 /* Compare two fsmap items. */
 static int ext4_getfsmap_compare(void *priv,
-				 struct list_head *a,
-				 struct list_head *b)
+				 const struct list_head *a,
+				 const struct list_head *b)
 {
 	struct ext4_fsmap *fa;
 	struct ext4_fsmap *fb;
diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 9567520d79f7..c06a6cdf05de 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -1732,7 +1732,8 @@ void gfs2_glock_complete(struct gfs2_glock *gl, int ret)
 	spin_unlock(&gl->gl_lockref.lock);
 }
 
-static int glock_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int glock_cmp(void *priv, const struct list_head *a,
+		     const struct list_head *b)
 {
 	struct gfs2_glock *gla, *glb;
 
diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 6410281546f9..88649b43fcff 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -695,7 +695,7 @@ void log_flush_wait(struct gfs2_sbd *sdp)
 	}
 }
 
-static int ip_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int ip_cmp(void *priv, const struct list_head *a, const struct list_head *b)
 {
 	struct gfs2_inode *ipa, *ipb;
 
diff --git a/fs/gfs2/lops.c b/fs/gfs2/lops.c
index a82f4747aa8d..b4809967efc6 100644
--- a/fs/gfs2/lops.c
+++ b/fs/gfs2/lops.c
@@ -634,7 +634,8 @@ static void gfs2_check_magic(struct buffer_head *bh)
 	kunmap_atomic(kaddr);
 }
 
-static int blocknr_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int blocknr_cmp(void *priv, const struct list_head *a,
+		       const struct list_head *b)
 {
 	struct gfs2_bufdata *bda, *bdb;
 
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 414769a6ad11..0129e6bab985 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -1155,7 +1155,8 @@ iomap_ioend_try_merge(struct iomap_ioend *ioend, struct list_head *more_ioends,
 EXPORT_SYMBOL_GPL(iomap_ioend_try_merge);
 
 static int
-iomap_ioend_compare(void *priv, struct list_head *a, struct list_head *b)
+iomap_ioend_compare(void *priv, const struct list_head *a,
+		const struct list_head *b)
 {
 	struct iomap_ioend *ia = container_of(a, struct iomap_ioend, io_list);
 	struct iomap_ioend *ib = container_of(b, struct iomap_ioend, io_list);
diff --git a/fs/ubifs/gc.c b/fs/ubifs/gc.c
index a4aaeea63893..dc3e26e9ed7b 100644
--- a/fs/ubifs/gc.c
+++ b/fs/ubifs/gc.c
@@ -102,7 +102,8 @@ static int switch_gc_head(struct ubifs_info *c)
  * This function compares data nodes @a and @b. Returns %1 if @a has greater
  * inode or block number, and %-1 otherwise.
  */
-static int data_nodes_cmp(void *priv, struct list_head *a, struct list_head *b)
+static int data_nodes_cmp(void *priv, const struct list_head *a,
+			  const struct list_head *b)
 {
 	ino_t inuma, inumb;
 	struct ubifs_info *c = priv;
@@ -145,8 +146,8 @@ static int data_nodes_cmp(void *priv, struct list_head *a, struct list_head *b)
  * first and sorted by length in descending order. Directory entry nodes go
  * after inode nodes and are sorted in ascending hash valuer order.
  */
-static int nondata_nodes_cmp(void *priv, struct list_head *a,
-			     struct list_head *b)
+static int nondata_nodes_cmp(void *priv, const struct list_head *a,
+			     const struct list_head *b)
 {
 	ino_t inuma, inumb;
 	struct ubifs_info *c = priv;
diff --git a/fs/ubifs/replay.c b/fs/ubifs/replay.c
index 0f8a6a16421b..4d17e5382b74 100644
--- a/fs/ubifs/replay.c
+++ b/fs/ubifs/replay.c
@@ -298,8 +298,8 @@ static int apply_replay_entry(struct ubifs_info *c, struct replay_entry *r)
  * entries @a and @b by comparing their sequence numer.  Returns %1 if @a has
  * greater sequence number and %-1 otherwise.
  */
-static int replay_entries_cmp(void *priv, struct list_head *a,
-			      struct list_head *b)
+static int replay_entries_cmp(void *priv, const struct list_head *a,
+			      const struct list_head *b)
 {
 	struct ubifs_info *c = priv;
 	struct replay_entry *ra, *rb;
diff --git a/fs/xfs/scrub/bitmap.c b/fs/xfs/scrub/bitmap.c
index f88694f22d05..813b5f219113 100644
--- a/fs/xfs/scrub/bitmap.c
+++ b/fs/xfs/scrub/bitmap.c
@@ -63,8 +63,8 @@ xbitmap_init(
 static int
 xbitmap_range_cmp(
 	void			*priv,
-	struct list_head	*a,
-	struct list_head	*b)
+	const struct list_head	*a,
+	const struct list_head	*b)
 {
 	struct xbitmap_range	*ap;
 	struct xbitmap_range	*bp;
diff --git a/fs/xfs/xfs_bmap_item.c b/fs/xfs/xfs_bmap_item.c
index 2344757ede63..e3a691937e92 100644
--- a/fs/xfs/xfs_bmap_item.c
+++ b/fs/xfs/xfs_bmap_item.c
@@ -265,8 +265,8 @@ xfs_trans_log_finish_bmap_update(
 static int
 xfs_bmap_update_diff_items(
 	void				*priv,
-	struct list_head		*a,
-	struct list_head		*b)
+	const struct list_head		*a,
+	const struct list_head		*b)
 {
 	struct xfs_bmap_intent		*ba;
 	struct xfs_bmap_intent		*bb;
diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 37a1d12762d8..592800c8852f 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -2124,9 +2124,9 @@ xfs_buf_delwri_queue(
  */
 static int
 xfs_buf_cmp(
-	void		*priv,
-	struct list_head *a,
-	struct list_head *b)
+	void			*priv,
+	const struct list_head	*a,
+	const struct list_head	*b)
 {
 	struct xfs_buf	*ap = container_of(a, struct xfs_buf, b_list);
 	struct xfs_buf	*bp = container_of(b, struct xfs_buf, b_list);
diff --git a/fs/xfs/xfs_extent_busy.c b/fs/xfs/xfs_extent_busy.c
index ef17c1f6db32..a4075685d9eb 100644
--- a/fs/xfs/xfs_extent_busy.c
+++ b/fs/xfs/xfs_extent_busy.c
@@ -629,8 +629,8 @@ xfs_extent_busy_wait_all(
 int
 xfs_extent_busy_ag_cmp(
 	void			*priv,
-	struct list_head	*l1,
-	struct list_head	*l2)
+	const struct list_head	*l1,
+	const struct list_head	*l2)
 {
 	struct xfs_extent_busy	*b1 =
 		container_of(l1, struct xfs_extent_busy, list);
diff --git a/fs/xfs/xfs_extent_busy.h b/fs/xfs/xfs_extent_busy.h
index 990ab3891971..8aea07100092 100644
--- a/fs/xfs/xfs_extent_busy.h
+++ b/fs/xfs/xfs_extent_busy.h
@@ -58,7 +58,8 @@ void
 xfs_extent_busy_wait_all(struct xfs_mount *mp);
 
 int
-xfs_extent_busy_ag_cmp(void *priv, struct list_head *a, struct list_head *b);
+xfs_extent_busy_ag_cmp(void *priv, const struct list_head *a,
+	const struct list_head *b);
 
 static inline void xfs_extent_busy_sort(struct list_head *list)
 {
diff --git a/fs/xfs/xfs_extfree_item.c b/fs/xfs/xfs_extfree_item.c
index 93223ebb3372..2424230ca2c3 100644
--- a/fs/xfs/xfs_extfree_item.c
+++ b/fs/xfs/xfs_extfree_item.c
@@ -397,8 +397,8 @@ xfs_trans_free_extent(
 static int
 xfs_extent_free_diff_items(
 	void				*priv,
-	struct list_head		*a,
-	struct list_head		*b)
+	const struct list_head		*a,
+	const struct list_head		*b)
 {
 	struct xfs_mount		*mp = priv;
 	struct xfs_extent_free_item	*ra;
diff --git a/fs/xfs/xfs_refcount_item.c b/fs/xfs/xfs_refcount_item.c
index 07ebccbbf4df..746f4eda724c 100644
--- a/fs/xfs/xfs_refcount_item.c
+++ b/fs/xfs/xfs_refcount_item.c
@@ -269,8 +269,8 @@ xfs_trans_log_finish_refcount_update(
 static int
 xfs_refcount_update_diff_items(
 	void				*priv,
-	struct list_head		*a,
-	struct list_head		*b)
+	const struct list_head		*a,
+	const struct list_head		*b)
 {
 	struct xfs_mount		*mp = priv;
 	struct xfs_refcount_intent	*ra;
diff --git a/fs/xfs/xfs_rmap_item.c b/fs/xfs/xfs_rmap_item.c
index 49cebd68b672..dc4f0c9f0897 100644
--- a/fs/xfs/xfs_rmap_item.c
+++ b/fs/xfs/xfs_rmap_item.c
@@ -337,8 +337,8 @@ xfs_trans_log_finish_rmap_update(
 static int
 xfs_rmap_update_diff_items(
 	void				*priv,
-	struct list_head		*a,
-	struct list_head		*b)
+	const struct list_head		*a,
+	const struct list_head		*b)
 {
 	struct xfs_mount		*mp = priv;
 	struct xfs_rmap_intent		*ra;
diff --git a/include/linux/list_sort.h b/include/linux/list_sort.h
index 20f178c24e9d..453105f74e05 100644
--- a/include/linux/list_sort.h
+++ b/include/linux/list_sort.h
@@ -6,8 +6,9 @@
 
 struct list_head;
 
+typedef int __attribute__((nonnull(2,3))) (*list_cmp_func_t)(void *,
+		const struct list_head *, const struct list_head *);
+
 __attribute__((nonnull(2,3)))
-void list_sort(void *priv, struct list_head *head,
-	       int (*cmp)(void *priv, struct list_head *a,
-			  struct list_head *b));
+void list_sort(void *priv, struct list_head *head, list_cmp_func_t cmp);
 #endif
diff --git a/lib/list_sort.c b/lib/list_sort.c
index 52f0c258c895..a926d96ffd44 100644
--- a/lib/list_sort.c
+++ b/lib/list_sort.c
@@ -7,16 +7,13 @@
 #include <linux/list_sort.h>
 #include <linux/list.h>
 
-typedef int __attribute__((nonnull(2,3))) (*cmp_func)(void *,
-		struct list_head const *, struct list_head const *);
-
 /*
  * Returns a list organized in an intermediate format suited
  * to chaining of merge() calls: null-terminated, no reserved or
  * sentinel head node, "prev" links not maintained.
  */
 __attribute__((nonnull(2,3,4)))
-static struct list_head *merge(void *priv, cmp_func cmp,
+static struct list_head *merge(void *priv, list_cmp_func_t cmp,
 				struct list_head *a, struct list_head *b)
 {
 	struct list_head *head, **tail = &head;
@@ -52,7 +49,7 @@ static struct list_head *merge(void *priv, cmp_func cmp,
  * throughout.
  */
 __attribute__((nonnull(2,3,4,5)))
-static void merge_final(void *priv, cmp_func cmp, struct list_head *head,
+static void merge_final(void *priv, list_cmp_func_t cmp, struct list_head *head,
 			struct list_head *a, struct list_head *b)
 {
 	struct list_head *tail = head;
@@ -185,9 +182,7 @@ static void merge_final(void *priv, cmp_func cmp, struct list_head *head,
  * 2^(k+1) - 1 (second merge of case 5 when x == 2^(k-1) - 1).
  */
 __attribute__((nonnull(2,3)))
-void list_sort(void *priv, struct list_head *head,
-		int (*cmp)(void *priv, struct list_head *a,
-			struct list_head *b))
+void list_sort(void *priv, struct list_head *head, list_cmp_func_t cmp)
 {
 	struct list_head *list = head->next, *pending = NULL;
 	size_t count = 0;	/* Count of pending */
@@ -227,7 +222,7 @@ void list_sort(void *priv, struct list_head *head,
 		if (likely(bits)) {
 			struct list_head *a = *tail, *b = a->prev;
 
-			a = merge(priv, (cmp_func)cmp, b, a);
+			a = merge(priv, cmp, b, a);
 			/* Install the merged result in place of the inputs */
 			a->prev = b->prev;
 			*tail = a;
@@ -249,10 +244,10 @@ void list_sort(void *priv, struct list_head *head,
 
 		if (!next)
 			break;
-		list = merge(priv, (cmp_func)cmp, pending, list);
+		list = merge(priv, cmp, pending, list);
 		pending = next;
 	}
 	/* The final merge, rebuilding prev links */
-	merge_final(priv, (cmp_func)cmp, head, pending, list);
+	merge_final(priv, cmp, head, pending, list);
 }
 EXPORT_SYMBOL(list_sort);
diff --git a/lib/test_list_sort.c b/lib/test_list_sort.c
index 1f017d3b610e..00daaf23316f 100644
--- a/lib/test_list_sort.c
+++ b/lib/test_list_sort.c
@@ -56,7 +56,8 @@ static int __init check(struct debug_el *ela, struct debug_el *elb)
 	return 0;
 }
 
-static int __init cmp(void *priv, struct list_head *a, struct list_head *b)
+static int __init cmp(void *priv, const struct list_head *a,
+		      const struct list_head *b)
 {
 	struct debug_el *ela, *elb;
 
diff --git a/net/tipc/name_table.c b/net/tipc/name_table.c
index ee5ac40ea2b6..f8141443f2e2 100644
--- a/net/tipc/name_table.c
+++ b/net/tipc/name_table.c
@@ -397,8 +397,8 @@ static struct publication *tipc_service_remove_publ(struct service_range *sr,
  * Code reused: time_after32() for the same purpose
  */
 #define publication_after(pa, pb) time_after32((pa)->id, (pb)->id)
-static int tipc_publ_sort(void *priv, struct list_head *a,
-			  struct list_head *b)
+static int tipc_publ_sort(void *priv, const struct list_head *a,
+			  const struct list_head *b)
 {
 	struct publication *pa, *pb;
 
-- 
cgit