arm64: Move patching utilities out of instruction encoding/decoding

Files insn.[c|h] containt some functions used for instruction patching.
In order to reuse the instruction encoder/decoder, move the patching
utilities to their own file.

Signed-off-by: Julien Thierry <jthierry@redhat.com>
Link: https://lore.kernel.org/r/20210303170536.1838032-2-jthierry@redhat.com
[will: Include patching.h in insn.h to fix header mess; add __ASSEMBLY__ guards]
Signed-off-by: Will Deacon <will@kernel.org>

Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 148 insertions, 0 deletions

diff --git a/arch/arm64/kernel/patching.c b/arch/arm64/kernel/patching.c
new file mode 100644
index 000000000000..9d050e33901b
--- /dev/null
+++ b/arch/arm64/kernel/patching.c
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/smp.h>
+#include <linux/spinlock.h>
+#include <linux/stop_machine.h>
+#include <linux/uaccess.h>
+
+#include <asm/cacheflush.h>
+#include <asm/fixmap.h>
+#include <asm/kprobes.h>
+#include <asm/sections.h>
+
+static DEFINE_RAW_SPINLOCK(patch_lock);
+
+static bool is_exit_text(unsigned long addr)
+{
+	/* discarded with init text/data */
+	return system_state < SYSTEM_RUNNING &&
+		addr >= (unsigned long)__exittext_begin &&
+		addr < (unsigned long)__exittext_end;
+}
+
+static bool is_image_text(unsigned long addr)
+{
+	return core_kernel_text(addr) || is_exit_text(addr);
+}
+
+static void __kprobes *patch_map(void *addr, int fixmap)
+{
+	unsigned long uintaddr = (uintptr_t) addr;
+	bool image = is_image_text(uintaddr);
+	struct page *page;
+
+	if (image)
+		page = phys_to_page(__pa_symbol(addr));
+	else if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
+		page = vmalloc_to_page(addr);
+	else
+		return addr;
+
+	BUG_ON(!page);
+	return (void *)set_fixmap_offset(fixmap, page_to_phys(page) +
+			(uintaddr & ~PAGE_MASK));
+}
+
+static void __kprobes patch_unmap(int fixmap)
+{
+	clear_fixmap(fixmap);
+}
+/*
+ * In ARMv8-A, A64 instructions have a fixed length of 32 bits and are always
+ * little-endian.
+ */
+int __kprobes aarch64_insn_read(void *addr, u32 *insnp)
+{
+	int ret;
+	__le32 val;
+
+	ret = copy_from_kernel_nofault(&val, addr, AARCH64_INSN_SIZE);
+	if (!ret)
+		*insnp = le32_to_cpu(val);
+
+	return ret;
+}
+
+static int __kprobes __aarch64_insn_write(void *addr, __le32 insn)
+{
+	void *waddr = addr;
+	unsigned long flags = 0;
+	int ret;
+
+	raw_spin_lock_irqsave(&patch_lock, flags);
+	waddr = patch_map(addr, FIX_TEXT_POKE0);
+
+	ret = copy_to_kernel_nofault(waddr, &insn, AARCH64_INSN_SIZE);
+
+	patch_unmap(FIX_TEXT_POKE0);
+	raw_spin_unlock_irqrestore(&patch_lock, flags);
+
+	return ret;
+}
+
+int __kprobes aarch64_insn_write(void *addr, u32 insn)
+{
+	return __aarch64_insn_write(addr, cpu_to_le32(insn));
+}
+
+int __kprobes aarch64_insn_patch_text_nosync(void *addr, u32 insn)
+{
+	u32 *tp = addr;
+	int ret;
+
+	/* A64 instructions must be word aligned */
+	if ((uintptr_t)tp & 0x3)
+		return -EINVAL;
+
+	ret = aarch64_insn_write(tp, insn);
+	if (ret == 0)
+		__flush_icache_range((uintptr_t)tp,
+				     (uintptr_t)tp + AARCH64_INSN_SIZE);
+
+	return ret;
+}
+
+struct aarch64_insn_patch {
+	void		**text_addrs;
+	u32		*new_insns;
+	int		insn_cnt;
+	atomic_t	cpu_count;
+};
+
+static int __kprobes aarch64_insn_patch_text_cb(void *arg)
+{
+	int i, ret = 0;
+	struct aarch64_insn_patch *pp = arg;
+
+	/* The first CPU becomes master */
+	if (atomic_inc_return(&pp->cpu_count) == 1) {
+		for (i = 0; ret == 0 && i < pp->insn_cnt; i++)
+			ret = aarch64_insn_patch_text_nosync(pp->text_addrs[i],
+							     pp->new_insns[i]);
+		/* Notify other processors with an additional increment. */
+		atomic_inc(&pp->cpu_count);
+	} else {
+		while (atomic_read(&pp->cpu_count) <= num_online_cpus())
+			cpu_relax();
+		isb();
+	}
+
+	return ret;
+}
+
+int __kprobes aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt)
+{
+	struct aarch64_insn_patch patch = {
+		.text_addrs = addrs,
+		.new_insns = insns,
+		.insn_cnt = cnt,
+		.cpu_count = ATOMIC_INIT(0),
+	};
+
+	if (cnt <= 0)
+		return -EINVAL;
+
+	return stop_machine_cpuslocked(aarch64_insn_patch_text_cb, &patch,
+				       cpu_online_mask);
+}