Re: [PATCH bpf-next 2/3] arm64: patching: Add aarch64_insn_copy()

[Song Liu]

On Mon, Jun 5, 2023 at 12:40 AM Puranjay Mohan <puranjay12@xxxxxxxxx> wrote:
>
> This will be used by BPF JIT compiler to dump JITed binary to a RX huge
> page, and thus allow multiple BPF programs sharing the a huge (2MB)
> page.
>
> The bpf_prog_pack allocator that implements the above feature allocates
> a RX/RW buffer pair. The JITed code is written to the RW buffer and then
> this function will be used to copy the code from RW to RX buffer.
>
> Signed-off-by: Puranjay Mohan <puranjay12@xxxxxxxxx>

Acked-by: Song Liu <song@xxxxxxxxxx>

With a nit below.

> ---
>  arch/arm64/include/asm/patching.h |  1 +
>  arch/arm64/kernel/patching.c      | 39 +++++++++++++++++++++++++++++++
>  2 files changed, 40 insertions(+)
>
> diff --git a/arch/arm64/include/asm/patching.h b/arch/arm64/include/asm/patching.h
> index 68908b82b168..dba9eb392bf1 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);
> +void *aarch64_insn_copy(void *addr, const void *opcode, 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..48c710f6a1ff 100644
> --- a/arch/arm64/kernel/patching.c
> +++ b/arch/arm64/kernel/patching.c
> @@ -105,6 +105,45 @@ noinstr int aarch64_insn_write_literal_u64(void *addr, u64 val)
>         return ret;
>  }
>
> +/**
> + * aarch64_insn_copy - Copy instructions into (an unused part of) RX memory
> + * @addr: address to modify
> + * @opcode: source of the copy
> + * @len: length to copy
> + *
> + * Useful for JITs to dump new code blocks into unused regions of RX memory.
> + */

nit:
I understand "addr" and "opcode" are used by x86 text_poke_copy(). But maybe
we should call them "dst" and "src" or "to" and "from" or something similar?

Thanks,
Song

> +noinstr void *aarch64_insn_copy(void *addr, const void *opcode, size_t len)
> +{
> +       unsigned long flags;
> +       size_t patched = 0;
> +       size_t size;
> +       void *waddr;
> +       void *dst;
> +       int ret;
> +
> +       raw_spin_lock_irqsave(&patch_lock, flags);
> +
> +       while (patched < len) {
> +               dst = addr + patched;
> +               size = min_t(size_t, PAGE_SIZE - offset_in_page(dst),
> +                            len - patched);
> +
> +               waddr = patch_map(dst, FIX_TEXT_POKE0);
> +               ret = copy_to_kernel_nofault(waddr, opcode + patched, size);
> +               patch_unmap(FIX_TEXT_POKE0);
> +
> +               if (ret < 0) {
> +                       raw_spin_unlock_irqrestore(&patch_lock, flags);
> +                       return NULL;
> +               }
> +               patched += size;
> +       }
> +       raw_spin_unlock_irqrestore(&patch_lock, flags);
> +
> +       return addr;
> +}
> +
>  int __kprobes aarch64_insn_patch_text_nosync(void *addr, u32 insn)
>  {
>         u32 *tp = addr;
> --
> 2.39.2
>