Re: [PATCH v4 1/5] powerpc/bpf: implement bpf_arch_text_copy

[Song Liu <song@xxxxxxxxxx>]

On Fri, Sep 8, 2023 at 6:28 AM Hari Bathini <hbathini@xxxxxxxxxxxxx> wrote:
>
> bpf_arch_text_copy is used to dump JITed binary to RX page, allowing
> multiple BPF programs to share the same page. Use patch_instruction()
> to implement it.
>
> Signed-off-by: Hari Bathini <hbathini@xxxxxxxxxxxxx>
> ---
>  arch/powerpc/net/bpf_jit_comp.c | 41 ++++++++++++++++++++++++++++++++-
>  1 file changed, 40 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index 37043dfc1add..4f896222c579 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -13,9 +13,12 @@
>  #include <linux/netdevice.h>
>  #include <linux/filter.h>
>  #include <linux/if_vlan.h>
> -#include <asm/kprobes.h>
> +#include <linux/memory.h>
>  #include <linux/bpf.h>
>
> +#include <asm/kprobes.h>
> +#include <asm/code-patching.h>
> +
>  #include "bpf_jit.h"
>
>  static void bpf_jit_fill_ill_insns(void *area, unsigned int size)
> @@ -23,6 +26,28 @@ static void bpf_jit_fill_ill_insns(void *area, unsigned int size)
>         memset32(area, BREAKPOINT_INSTRUCTION, size / 4);
>  }
>
> +/*
> + * Patch 'len' bytes of instructions from opcode to addr, one instruction
> + * at a time. Returns addr on success. ERR_PTR(-EINVAL), otherwise.
> + */
> +static void *bpf_patch_instructions(void *addr, void *opcode, size_t len, bool fill_insn)
> +{
> +       while (len > 0) {
> +               ppc_inst_t insn = ppc_inst_read(opcode);
> +               int ilen = ppc_inst_len(insn);
> +
> +               if (patch_instruction(addr, insn))
> +                       return ERR_PTR(-EINVAL);

Is there any reason we have to do this one instruction at a time? I believe
Christophe Leroy pointed out the same in an earlier version?

Thanks,
Song

> +
> +               len -= ilen;
> +               addr = addr + ilen;
> +               if (!fill_insn)
> +                       opcode = opcode + ilen;
> +       }
> +
> +       return addr;
> +}
> +
>  int bpf_jit_emit_exit_insn(u32 *image, struct codegen_context *ctx, int tmp_reg, long exit_addr)
>  {
>         if (!exit_addr || is_offset_in_branch_range(exit_addr - (ctx->idx * 4))) {
> @@ -274,3 +299,17 @@ int bpf_add_extable_entry(struct bpf_prog *fp, u32 *image, int pass, struct code
>         ctx->exentry_idx++;
>         return 0;
>  }
> +
> +void *bpf_arch_text_copy(void *dst, void *src, size_t len)
> +{
> +       void *ret;
> +
> +       if (WARN_ON_ONCE(core_kernel_text((unsigned long)dst)))
> +               return ERR_PTR(-EINVAL);
> +
> +       mutex_lock(&text_mutex);
> +       ret = bpf_patch_instructions(dst, src, len, false);
> +       mutex_unlock(&text_mutex);
> +
> +       return ret;
> +}