linux-kernel - Re: [PATCH v4 bpf-next 3/8] bpf: introduce bpf_arch_text_invalidate for bpf_prog

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Date:   Tue, 24 May 2022 10:20:17 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Song Liu <song@...nel.org>
Cc:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        linux-mm@...ck.org, ast@...nel.org, daniel@...earbox.net,
        peterz@...radead.org, mcgrof@...nel.org,
        torvalds@...ux-foundation.org, rick.p.edgecombe@...el.com,
        kernel-team@...com
Subject: Re: [PATCH v4 bpf-next 3/8] bpf: introduce bpf_arch_text_invalidate
 for bpf_prog_pack

On Fri, May 20, 2022 at 04:57:53PM -0700, Song Liu wrote:
> Introduce bpf_arch_text_invalidate and use it to fill unused part of the
> bpf_prog_pack with illegal instructions when a BPF program is freed.
> 
> Signed-off-by: Song Liu <song@...nel.org>
> ---
>  arch/x86/net/bpf_jit_comp.c | 5 +++++
>  include/linux/bpf.h         | 1 +
>  kernel/bpf/core.c           | 8 ++++++++
>  3 files changed, 14 insertions(+)
> 
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index a2b6d197c226..f298b18a9a3d 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -228,6 +228,11 @@ static void jit_fill_hole(void *area, unsigned int size)
>  	memset(area, 0xcc, size);
>  }
>  
> +int bpf_arch_text_invalidate(void *dst, size_t len)
> +{
> +	return IS_ERR_OR_NULL(text_poke_set(dst, 0xcc, len));
> +}
> +
>  struct jit_context {
>  	int cleanup_addr; /* Epilogue code offset */
>  
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index cc4d5e394031..a9b1875212f6 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -2365,6 +2365,7 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
>  		       void *addr1, void *addr2);
>  
>  void *bpf_arch_text_copy(void *dst, void *src, size_t len);
> +int bpf_arch_text_invalidate(void *dst, size_t len);
>  
>  struct btf_id_set;
>  bool btf_id_set_contains(const struct btf_id_set *set, u32 id);
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 2d0c9d4696ad..cacd8684c3c4 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -968,6 +968,9 @@ static void bpf_prog_pack_free(struct bpf_binary_header *hdr)
>  	nbits = BPF_PROG_SIZE_TO_NBITS(hdr->size);
>  	pos = ((unsigned long)hdr - (unsigned long)pack_ptr) >> BPF_PROG_CHUNK_SHIFT;
>  
> +	WARN_ONCE(bpf_arch_text_invalidate(hdr, hdr->size),
> +		  "bpf_prog_pack bug: missing bpf_arch_text_invalidate?\n");

Why is this a WARN?

What happens if bpf_arch_text_invalidate() is implemented but returns an error?

> +
>  	bitmap_clear(pack->bitmap, pos, nbits);
>  	if (bitmap_find_next_zero_area(pack->bitmap, bpf_prog_chunk_count(), 0,
>  				       bpf_prog_chunk_count(), 0) == 0) {
> @@ -2740,6 +2743,11 @@ void * __weak bpf_arch_text_copy(void *dst, void *src, size_t len)
>  	return ERR_PTR(-ENOTSUPP);
>  }
>  
> +int __weak bpf_arch_text_invalidate(void *dst, size_t len)
> +{
> +	return -ENOTSUPP;
> +}
> +
>  DEFINE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
>  EXPORT_SYMBOL(bpf_stats_enabled_key);
>  
> -- 
> 2.30.2
> 
> 

-- 
Sincerely yours,
Mike.