Re: [PATCH 2/4] net/bpf: refactor freeing of executable allocations

[Y Song]

On Sat, Nov 17, 2018 at 6:58 PM Ard Biesheuvel
<ard.biesheuvel@xxxxxxxxxx> wrote:
>
> All arch overrides of the __weak bpf_jit_free() amount to the same
> thing: the allocated memory was never mapped read-only, and so
> it does not have to be remapped to read-write before being freed.
>
> So in preparation of permitting arches to serve allocations for BPF
> JIT programs from other regions than the module region, refactor
> the existing bpf_jit_free() implementations to use the shared code
> where possible, and only specialize the remap and free operations.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> ---
>  arch/mips/net/bpf_jit.c           |  7 ++-----
>  arch/powerpc/net/bpf_jit_comp.c   |  7 ++-----
>  arch/powerpc/net/bpf_jit_comp64.c |  9 +++------
>  arch/sparc/net/bpf_jit_comp_32.c  |  7 ++-----
>  kernel/bpf/core.c                 | 15 +++++----------
>  5 files changed, 14 insertions(+), 31 deletions(-)
>
> diff --git a/arch/mips/net/bpf_jit.c b/arch/mips/net/bpf_jit.c
> index 1b69897274a1..5696bd7dccc7 100644
> --- a/arch/mips/net/bpf_jit.c
> +++ b/arch/mips/net/bpf_jit.c
> @@ -1261,10 +1261,7 @@ void bpf_jit_compile(struct bpf_prog *fp)
>         kfree(ctx.offsets);
>  }
>
> -void bpf_jit_free(struct bpf_prog *fp)
> +void bpf_jit_binary_free(struct bpf_binary_header *hdr)
>  {
> -       if (fp->jited)
> -               bpf_jit_binary_free(bpf_jit_binary_hdr(fp));
> -
> -       bpf_prog_unlock_free(fp);
> +       module_memfree(hdr);
>  }
> diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
> index a1ea1ea6b40d..5b5ce4a1b44b 100644
> --- a/arch/powerpc/net/bpf_jit_comp.c
> +++ b/arch/powerpc/net/bpf_jit_comp.c
> @@ -680,10 +680,7 @@ void bpf_jit_compile(struct bpf_prog *fp)
>         return;
>  }
>
> -void bpf_jit_free(struct bpf_prog *fp)
> +void bpf_jit_binary_free(struct bpf_binary_header *hdr)
>  {
> -       if (fp->jited)
> -               bpf_jit_binary_free(bpf_jit_binary_hdr(fp));
> -
> -       bpf_prog_unlock_free(fp);
> +       module_memfree(hdr);
>  }
> diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
> index 84c8f013a6c6..f64f1294bd62 100644
> --- a/arch/powerpc/net/bpf_jit_comp64.c
> +++ b/arch/powerpc/net/bpf_jit_comp64.c
> @@ -1021,11 +1021,8 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
>         return fp;
>  }
>
> -/* Overriding bpf_jit_free() as we don't set images read-only. */
> -void bpf_jit_free(struct bpf_prog *fp)
> +/* Overriding bpf_jit_binary_free() as we don't set images read-only. */
> +void bpf_jit_binary_free(struct bpf_binary_header *hdr)
>  {
> -       if (fp->jited)
> -               bpf_jit_binary_free(bpf_jit_binary_hdr(fp));
> -
> -       bpf_prog_unlock_free(fp);
> +       module_memfree(hdr);
>  }
> diff --git a/arch/sparc/net/bpf_jit_comp_32.c b/arch/sparc/net/bpf_jit_comp_32.c
> index 01bda6bc9e7f..589950d152cc 100644
> --- a/arch/sparc/net/bpf_jit_comp_32.c
> +++ b/arch/sparc/net/bpf_jit_comp_32.c
> @@ -756,10 +756,7 @@ cond_branch:                       f_offset = addrs[i + filter[i].jf];
>         return;
>  }
>
> -void bpf_jit_free(struct bpf_prog *fp)
> +void bpf_jit_binary_free(struct bpf_binary_header *hdr)
>  {
> -       if (fp->jited)
> -               bpf_jit_binary_free(bpf_jit_binary_hdr(fp));
> -
> -       bpf_prog_unlock_free(fp);
> +       module_memfree(hdr);
>  }
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 1a796e0799ec..29f766dac203 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -646,25 +646,20 @@ bpf_jit_binary_alloc(unsigned int proglen, u8 **image_ptr,
>         return hdr;
>  }
>
> -void bpf_jit_binary_free(struct bpf_binary_header *hdr)
> +void __weak bpf_jit_binary_free(struct bpf_binary_header *hdr)
>  {
> -       u32 pages = hdr->pages;
> -
> +       bpf_jit_binary_unlock_ro(hdr);
>         module_memfree(hdr);
> -       bpf_jit_uncharge_modmem(pages);
>  }
>
> -/* This symbol is only overridden by archs that have different
> - * requirements than the usual eBPF JITs, f.e. when they only
> - * implement cBPF JIT, do not set images read-only, etc.
> - */

Do you want to move the above comments to
new weak function bpf_jit_binary_free?

> -void __weak bpf_jit_free(struct bpf_prog *fp)
> +void bpf_jit_free(struct bpf_prog *fp)
>  {
>         if (fp->jited) {
>                 struct bpf_binary_header *hdr = bpf_jit_binary_hdr(fp);
> +               u32 pages = hdr->pages;
>
> -               bpf_jit_binary_unlock_ro(hdr);
>                 bpf_jit_binary_free(hdr);
> +               bpf_jit_uncharge_modmem(pages);
>
>                 WARN_ON_ONCE(!bpf_prog_kallsyms_verify_off(fp));
>         }
> --
> 2.17.1
>