linux-kernel - Re: [PATCH bpf-next] bpf: Increase size of BTF_ID_LIST without CONFIG_DEBUG_INFO

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Date:   Tue, 7 Mar 2023 07:26:59 -0800
From:   Tom Rix <trix@...hat.com>
To:     Nathan Chancellor <nathan@...nel.org>, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org
Cc:     martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, ndesaulniers@...gle.com,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, patches@...ts.linux.dev
Subject: Re: [PATCH bpf-next] bpf: Increase size of BTF_ID_LIST without
 CONFIG_DEBUG_INFO_BTF again


On 3/7/23 7:14 AM, Nathan Chancellor wrote:
> After commit 66e3a13e7c2c ("bpf: Add bpf_dynptr_slice and
> bpf_dynptr_slice_rdwr"), clang builds without CONFIG_DEBUG_INFO_BTF
> warn:
>
>    kernel/bpf/verifier.c:10298:24: warning: array index 16 is past the end of the array (that has type 'u32[16]' (aka 'unsigned int[16]')) [-Warray-bounds]
>                                       meta.func_id == special_kfunc_list[KF_bpf_dynptr_slice_rdwr]) {
>                                                       ^                  ~~~~~~~~~~~~~~~~~~~~~~~~
>    kernel/bpf/verifier.c:9150:1: note: array 'special_kfunc_list' declared here
>    BTF_ID_LIST(special_kfunc_list)
>    ^
>    include/linux/btf_ids.h:207:27: note: expanded from macro 'BTF_ID_LIST'
>    #define BTF_ID_LIST(name) static u32 __maybe_unused name[16];
>                              ^
>    1 warning generated.
>
> A warning of this nature was previously addressed by
> commit beb3d47d1d3d ("bpf: Fix a BTF_ID_LIST bug with
> CONFIG_DEBUG_INFO_BTF not set") but there have been new kfuncs added
> since then.
>
> Quadruple the size of the CONFIG_DEBUG_INFO_BTF=n definition so that
> this problem is unlikely to show up for some time.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1810
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>

This has a better commit message, let's use this one.

FWIW, gcc 13 -Warray-bounds, did not catch this.

Reviewed-by: Tom Rix <trix@...hat.com>

> ---
>   include/linux/btf_ids.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
> index 3a4f7cd882ca..00950cc03bff 100644
> --- a/include/linux/btf_ids.h
> +++ b/include/linux/btf_ids.h
> @@ -204,7 +204,7 @@ extern struct btf_id_set8 name;
>   
>   #else
>   
> -#define BTF_ID_LIST(name) static u32 __maybe_unused name[16];
> +#define BTF_ID_LIST(name) static u32 __maybe_unused name[64];
>   #define BTF_ID(prefix, name)
>   #define BTF_ID_FLAGS(prefix, name, ...)
>   #define BTF_ID_UNUSED
>
> ---
> base-commit: 36e5e391a25af28dc1f4586f95d577b38ff4ed72
> change-id: 20230307-bpf-kfuncs-warray-bounds-c2040e8ee7ee
>
> Best regards,