On Fri, Sep 08, 2023 at 02:43:19PM +0000, 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
> + * @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);
Do we need to use a specific instruction passed by the caller, or can we
hard-code a trapping instruction here?
If we don't care about the specific instruction, it'd be best to memset this to
0, as 0x00000000 is UDF #0 (which will trap), and that way memset can use DC
ZVA to zero the memory, which is faster than 4 bytes at a time.
If we did that, we can rename this to something like:
aarch64_insn_clear(void *dst, size_t len)
> + 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);
Assuming the point of this is to trap if/when we accidentally execute the freed
instructions, we need an IPI here, and so this should use flush_icache_range()
or make it the caller's responsibility to do so.
Mark.
> +
> + return 0;
> +}
> +
> int __kprobes aarch64_insn_patch_text_nosync(void *addr, u32 insn)
> {
> u32 *tp = addr;
> --
> 2.40.1
>
>
