Re: [PATCH bpf-next 1/2] bpf: Take return from set_memory_ro() into account with bpf_prog_lock_ro()

[Hengqi Chen]

Hello Christophe,

On Sun, Feb 18, 2024 at 6:55 PM Christophe Leroy
<christophe.leroy@xxxxxxxxxx> wrote:
>
> set_memory_ro() can fail, leaving memory unprotected.
>
> Check its return and take it into account as an error.
>

I don't see a cover letter for this series, could you describe how
set_memory_ro() could fail.
(Most callsites of set_memory_ro() didn't check the return values)

And maybe craft a selftest to check the expected return values.

> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> ---
>  include/linux/filter.h | 5 +++--
>  kernel/bpf/core.c      | 4 +++-
>  kernel/bpf/verifier.c  | 4 +++-
>  3 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index fee070b9826e..fc0994dc5c72 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -881,14 +881,15 @@ bpf_ctx_narrow_access_offset(u32 off, u32 size, u32 size_default)
>
>  #define bpf_classic_proglen(fprog) (fprog->len * sizeof(fprog->filter[0]))
>
> -static inline void bpf_prog_lock_ro(struct bpf_prog *fp)
> +static inline int __must_check bpf_prog_lock_ro(struct bpf_prog *fp)
>  {
>  #ifndef CONFIG_BPF_JIT_ALWAYS_ON
>         if (!fp->jited) {
>                 set_vm_flush_reset_perms(fp);
> -               set_memory_ro((unsigned long)fp, fp->pages);
> +               return set_memory_ro((unsigned long)fp, fp->pages);
>         }
>  #endif
> +       return 0;
>  }
>
>  static inline void bpf_jit_binary_lock_ro(struct bpf_binary_header *hdr)
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 71c459a51d9e..c49619ef55d0 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2392,7 +2392,9 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_prog *fp, int *err)
>         }
>
>  finalize:
> -       bpf_prog_lock_ro(fp);
> +       *err = bpf_prog_lock_ro(fp);
> +       if (*err)
> +               return fp;
>
>         /* The tail call compatibility check can only be done at
>          * this late stage as we need to determine, if we deal
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index c5d68a9d8acc..1f831a6b4bbc 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -19020,7 +19020,9 @@ static int jit_subprogs(struct bpf_verifier_env *env)
>          * bpf_prog_load will add the kallsyms for the main program.
>          */
>         for (i = 1; i < env->subprog_cnt; i++) {
> -               bpf_prog_lock_ro(func[i]);
> +               err = bpf_prog_lock_ro(func[i]);
> +               if (err)
> +                       goto out_free;
>                 bpf_prog_kallsyms_add(func[i]);
>         }
>
> --
> 2.43.0
>
>