Merge branch 'kprobes: rethook: x86: Replace kretprobe trampoline with rethook'

Masami Hiramatsu says:

====================
Here are the 3rd version for generic kretprobe and kretprobe on x86 for
replacing the kretprobe trampoline with rethook. The previous version
is here[1]

[1] https://lore.kernel.org/all/164821817332.2373735.12048266953420821089.stgit@devnote2/T/#u

This version fixed typo and build issues for bpf-next and CONFIG_RETHOOK=y
error. I also add temporary mitigation lines for ANNOTATE_NOENDBR macro
issue for bpf-next tree [2/4].

This will be removed after merging kernel IBT series.

Background:

This rethook came from Jiri's request of multiple kprobe for bpf[2].
He tried to solve an issue that starting bpf with multiple kprobe will
take a long time because bpf-kprobe will wait for RCU grace period for
sync rcu events.

Jiri wanted to attach a single bpf handler to multiple kprobes and
he tried to introduce multiple-probe interface to kprobe. So I asked
him to use ftrace and kretprobe-like hook if it is only for the
function entry and exit, instead of adding ad-hoc interface
to kprobes.
For this purpose, I introduced the fprobe (kprobe like interface for
ftrace) with the rethook (this is a generic return hook feature for
fprobe exit handler)[3].

[2] https://lore.kernel.org/all/[email protected]/T/#u
[3] https://lore.kernel.org/all/164191321766.806991.7930388561276940676.stgit@devnote2/T/#u

The rethook is basically same as the kretprobe trampoline. I just made
it decoupled from kprobes. Eventually, the all arch dependent kretprobe
trampolines will be replaced with the rethook trampoline instead of
cloning and set HAVE_RETHOOK=y.
When I port the rethook for all arch which supports kretprobe, the
legacy kretprobe specific code (which is for CONFIG_KRETPROBE_ON_RETHOOK=n)
will be removed eventually.
====================

Acked-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Alexei Starovoitov <[email protected]>

1 files changed, 127 insertions, 0 deletions

diff --git a/arch/x86/kernel/rethook.c b/arch/x86/kernel/rethook.c
new file mode 100644
index 000000000000..8a1c0111ae79
--- /dev/null
+++ b/arch/x86/kernel/rethook.c
@@ -0,0 +1,127 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * x86 implementation of rethook. Mostly copied from arch/x86/kernel/kprobes/core.c.
+ */
+#include <linux/bug.h>
+#include <linux/rethook.h>
+#include <linux/kprobes.h>
+#include <linux/objtool.h>
+
+#include "kprobes/common.h"
+
+__visible void arch_rethook_trampoline_callback(struct pt_regs *regs);
+
+#ifndef ANNOTATE_NOENDBR
+#define ANNOTATE_NOENDBR
+#endif
+
+/*
+ * When a target function returns, this code saves registers and calls
+ * arch_rethook_trampoline_callback(), which calls the rethook handler.
+ */
+asm(
+	".text\n"
+	".global arch_rethook_trampoline\n"
+	".type arch_rethook_trampoline, @function\n"
+	"arch_rethook_trampoline:\n"
+#ifdef CONFIG_X86_64
+	ANNOTATE_NOENDBR	/* This is only jumped from ret instruction */
+	/* Push a fake return address to tell the unwinder it's a rethook. */
+	"	pushq $arch_rethook_trampoline\n"
+	UNWIND_HINT_FUNC
+	"       pushq $" __stringify(__KERNEL_DS) "\n"
+	/* Save the 'sp - 16', this will be fixed later. */
+	"	pushq %rsp\n"
+	"	pushfq\n"
+	SAVE_REGS_STRING
+	"	movq %rsp, %rdi\n"
+	"	call arch_rethook_trampoline_callback\n"
+	RESTORE_REGS_STRING
+	/* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
+	"	addq $16, %rsp\n"
+	"	popfq\n"
+#else
+	/* Push a fake return address to tell the unwinder it's a rethook. */
+	"	pushl $arch_rethook_trampoline\n"
+	UNWIND_HINT_FUNC
+	"	pushl %ss\n"
+	/* Save the 'sp - 8', this will be fixed later. */
+	"	pushl %esp\n"
+	"	pushfl\n"
+	SAVE_REGS_STRING
+	"	movl %esp, %eax\n"
+	"	call arch_rethook_trampoline_callback\n"
+	RESTORE_REGS_STRING
+	/* In the callback function, 'regs->flags' is copied to 'regs->ss'. */
+	"	addl $8, %esp\n"
+	"	popfl\n"
+#endif
+	ASM_RET
+	".size arch_rethook_trampoline, .-arch_rethook_trampoline\n"
+);
+NOKPROBE_SYMBOL(arch_rethook_trampoline);
+
+/*
+ * Called from arch_rethook_trampoline
+ */
+__used __visible void arch_rethook_trampoline_callback(struct pt_regs *regs)
+{
+	unsigned long *frame_pointer;
+
+	/* fixup registers */
+	regs->cs = __KERNEL_CS;
+#ifdef CONFIG_X86_32
+	regs->gs = 0;
+#endif
+	regs->ip = (unsigned long)&arch_rethook_trampoline;
+	regs->orig_ax = ~0UL;
+	regs->sp += 2*sizeof(long);
+	frame_pointer = (long *)(regs + 1);
+
+	/*
+	 * The return address at 'frame_pointer' is recovered by the
+	 * arch_rethook_fixup_return() which called from this
+	 * rethook_trampoline_handler().
+	 */
+	rethook_trampoline_handler(regs, (unsigned long)frame_pointer);
+
+	/*
+	 * Copy FLAGS to 'pt_regs::ss' so that arch_rethook_trapmoline()
+	 * can do RET right after POPF.
+	 */
+	*(unsigned long *)&regs->ss = regs->flags;
+}
+NOKPROBE_SYMBOL(arch_rethook_trampoline_callback);
+
+/*
+ * arch_rethook_trampoline() skips updating frame pointer. The frame pointer
+ * saved in arch_rethook_trampoline_callback() points to the real caller
+ * function's frame pointer. Thus the arch_rethook_trampoline() doesn't have
+ * a standard stack frame with CONFIG_FRAME_POINTER=y.
+ * Let's mark it non-standard function. Anyway, FP unwinder can correctly
+ * unwind without the hint.
+ */
+STACK_FRAME_NON_STANDARD_FP(arch_rethook_trampoline);
+
+/* This is called from rethook_trampoline_handler(). */
+void arch_rethook_fixup_return(struct pt_regs *regs,
+			       unsigned long correct_ret_addr)
+{
+	unsigned long *frame_pointer = (void *)(regs + 1);
+
+	/* Replace fake return address with real one. */
+	*frame_pointer = correct_ret_addr;
+}
+NOKPROBE_SYMBOL(arch_rethook_fixup_return);
+
+void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs, bool mcount)
+{
+	unsigned long *stack = (unsigned long *)regs->sp;
+
+	rh->ret_addr = stack[0];
+	rh->frame = regs->sp;
+
+	/* Replace the return addr with trampoline addr */
+	stack[0] = (unsigned long) arch_rethook_trampoline;
+}
+NOKPROBE_SYMBOL(arch_rethook_prepare);