[PATCH bpf-next v5 2/3] arm64: patching: Add aarch64_insn_set()

[Puranjay Mohan]

The BPF JIT needs to write invalid instructions to RX regions of memory
to invalidate removed BPF programs. This needs a function like memset()
that can work with RX memory.

Implement aarch64_insn_set() which is similar to text_poke_set() of x86.

Signed-off-by: Puranjay Mohan <puranjay12 at gmail.com>
---
 arch/arm64/include/asm/patching.h |  1 +
 arch/arm64/kernel/patching.c      | 40 +++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/arch/arm64/include/asm/patching.h b/arch/arm64/include/asm/patching.h
index f78a0409cbdb..551933338739 100644
--- a/arch/arm64/include/asm/patching.h
+++ b/arch/arm64/include/asm/patching.h
@@ -8,6 +8,7 @@ int aarch64_insn_read(void *addr, u32 *insnp);
 int aarch64_insn_write(void *addr, u32 insn);
 
 int aarch64_insn_write_literal_u64(void *addr, u64 val);
+int aarch64_insn_set(void *dst, const u32 insn, size_t len);
 void *aarch64_insn_copy(void *dst, const void *src, size_t len);
 
 int aarch64_insn_patch_text_nosync(void *addr, u32 insn);
diff --git a/arch/arm64/kernel/patching.c b/arch/arm64/kernel/patching.c
index 243d6ae8d2d8..63d9e0e77806 100644
--- a/arch/arm64/kernel/patching.c
+++ b/arch/arm64/kernel/patching.c
@@ -146,6 +146,46 @@ noinstr void *aarch64_insn_copy(void *dst, const void *src, size_t len)
 	return dst;
 }
 
+/**
+ * aarch64_insn_set - memset for RX memory regions.
+ * @dst: address to modify
+ * @c: value to set
+ * @len: length of memory region.
+ *
+ * Useful for JITs to fill regions of RX memory with illegal instructions.
+ */
+noinstr int aarch64_insn_set(void *dst, const u32 insn, size_t len)
+{
+	unsigned long flags;
+	size_t patched = 0;
+	size_t size;
+	void *waddr;
+	void *ptr;
+
+	/* A64 instructions must be word aligned */
+	if ((uintptr_t)dst & 0x3)
+		return -EINVAL;
+
+	raw_spin_lock_irqsave(&patch_lock, flags);
+
+	while (patched < len) {
+		ptr = dst + patched;
+		size = min_t(size_t, PAGE_SIZE - offset_in_page(ptr),
+			     len - patched);
+
+		waddr = patch_map(ptr, FIX_TEXT_POKE0);
+		memset32(waddr, insn, size / 4);
+		patch_unmap(FIX_TEXT_POKE0);
+
+		patched += size;
+	}
+	raw_spin_unlock_irqrestore(&patch_lock, flags);
+
+	caches_clean_inval_pou((uintptr_t)dst, (uintptr_t)dst + len);
+
+	return 0;
+}
+
 int __kprobes aarch64_insn_patch_text_nosync(void *addr, u32 insn)
 {
 	u32 *tp = addr;
-- 
2.40.1