Re: [PATCH bpf-next v7 1/2] arm64: patching: implement text_poke API

[Xu Kuohai]

On 1/25/2024 9:31 PM, Puranjay Mohan wrote:
> The text_poke API is used to implement functions like memcpy() and
> memset() for instruction memory (RO+X). The implementation is similar to
> the x86 version.
>
> This will be used by the BPF JIT to write and modify BPF programs. There
> could be more users of this in the future.
>
> Signed-off-by: Puranjay Mohan <puranjay12@xxxxxxxxx>
> ---
>   arch/arm64/include/asm/patching.h |  2 +
>   arch/arm64/kernel/patching.c      | 80 +++++++++++++++++++++++++++++++
>   2 files changed, 82 insertions(+)
>
> diff --git a/arch/arm64/include/asm/patching.h b/arch/arm64/include/asm/patching.h
> index 68908b82b168..587bdb91ab7a 100644
> --- a/arch/arm64/include/asm/patching.h
> +++ b/arch/arm64/include/asm/patching.h
> @@ -8,6 +8,8 @@ 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);
> +void *aarch64_insn_set(void *dst, u32 insn, size_t len);
> +void *aarch64_insn_copy(void *dst, void *src, size_t len);
>   
>   int aarch64_insn_patch_text_nosync(void *addr, u32 insn);
>   int aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt);
> diff --git a/arch/arm64/kernel/patching.c b/arch/arm64/kernel/patching.c
> index b4835f6d594b..5c2d34d890cf 100644
> --- a/arch/arm64/kernel/patching.c
> +++ b/arch/arm64/kernel/patching.c
> @@ -105,6 +105,86 @@ noinstr int aarch64_insn_write_literal_u64(void *addr, u64 val)
>   	return ret;
>   }
>   
> +typedef void text_poke_f(void *dst, void *src, size_t patched, size_t len);
> +

How about removing the argument 'patched' and passing 'src + patched' as the
second argument?

> +static void *__text_poke(text_poke_f func, void *addr, void *src, size_t len)
> +{
> +	unsigned long flags;
> +	size_t patched = 0;
> +	size_t size;
> +	void *waddr;
> +	void *ptr;
> +	int ret;
> +
> +	raw_spin_lock_irqsave(&patch_lock, flags);
> +
> +	while (patched < len) {
> +		ptr = addr + patched;
> +		size = min_t(size_t, PAGE_SIZE - offset_in_page(ptr),
> +			     len - patched);
> +
> +		waddr = patch_map(ptr, FIX_TEXT_POKE0);
> +		func(waddr, src, patched, size);
> +		patch_unmap(FIX_TEXT_POKE0);
> +
> +		if (ret < 0) {

Where is 'ret' assigned?

> +			raw_spin_unlock_irqrestore(&patch_lock, flags);
> +			return NULL;
> +		}
> +		patched += size;
> +	}
> +	raw_spin_unlock_irqrestore(&patch_lock, flags);
> +
> +	flush_icache_range((uintptr_t)addr, (uintptr_t)addr + len);
> +
> +	return addr;
> +}
> +
> +static void text_poke_memcpy(void *dst, void *src, size_t patched, size_t len)
> +{
> +	copy_to_kernel_nofault(dst, src + patched, len);
> +}
> +
> +static void text_poke_memset(void *dst, void *src, size_t patched, size_t len)
> +{
> +	u32 c = *(u32 *)src;
> +
> +	memset32(dst, c, len / 4);
> +}
> +
> +/**
> + * aarch64_insn_copy - Copy instructions into (an unused part of) RX memory
> + * @dst: address to modify
> + * @src: source of the copy
> + * @len: length to copy
> + *
> + * Useful for JITs to dump new code blocks into unused regions of RX memory.
> + */
> +noinstr void *aarch64_insn_copy(void *dst, void *src, size_t len)
> +{
> +	/* A64 instructions must be word aligned */
> +	if ((uintptr_t)dst & 0x3)
> +		return NULL;
> +
> +	return __text_poke(text_poke_memcpy, dst, src, len);
> +}
> +
> +/**
> + * aarch64_insn_set - memset for RX memory regions.
> + * @dst: address to modify
> + * @insn: value to set
> + * @len: length of memory region.
> + *
> + * Useful for JITs to fill regions of RX memory with illegal instructions.
> + */
> +noinstr void *aarch64_insn_set(void *dst, u32 insn, size_t len)
> +{
> +	if ((uintptr_t)dst & 0x3)
> +		return NULL;
> +
> +	return __text_poke(text_poke_memset, dst, &insn, len);
> +}
> +
>   int __kprobes aarch64_insn_patch_text_nosync(void *addr, u32 insn)
>   {
>   	u32 *tp = addr;