Re: [PATCH bpf-next v5 2/3] arm64: patching: Add aarch64_insn_set()
From: Xu Kuohai
Date: Thu Sep 21 2023 - 21:25:09 EST
On 9/21/2023 10:50 PM, Puranjay Mohan wrote:
Xu Kuohai <xukuohai@xxxxxxxxxxxxxxx> writes:
On 9/8/2023 10:43 PM, Puranjay Mohan wrote:
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@xxxxxxxxx>
---
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
insn
Thanks for catching.
+ * @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)
const is unnecessary
Will remove in next version.
+{
+ 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;
+}
+
this function shares most of the code with aarch64_insn_copy(), how about
extracting the shared code to a separate function?
I was thinking of writing it like the text_poke api of x86. Where you
can provide a function as an argument to work on a memory area.
Essentially, it will look like:
typedef int text_poke_f(void *dst, const void *src, size_t len);
static void *aarch64_insn_poke(text_poke_f func, void *addr, const void *src, size_t len)
We can call this function with a wrapper of `copy_to_kernel_nofault` for copy
and with a wrapper of memset32 for setting.
Do you think this is a good approach?
Sounds great, thanks.
int __kprobes aarch64_insn_patch_text_nosync(void *addr, u32 insn)
{
u32 *tp = addr;
Thanks,
Puranjay