linux-kernel - Re: [PATCH] kexec: Annotate struct crash_mem with __counted

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Date:   Sat, 23 Sep 2023 08:46:47 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Eric Biederman <ebiederm@...ssion.com>, kexec@...ts.infradead.org,
        Vivek Goyal <vgoyal@...hat.com>,
        Dave Young <dyoung@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] kexec: Annotate struct crash_mem with __counted_by

On 09/22/23 at 10:52am, Kees Cook wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> As found with Coccinelle[1], add __counted_by for struct crash_mem.
> 
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> 
> Cc: Eric Biederman <ebiederm@...ssion.com>
> Cc: kexec@...ts.infradead.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  include/linux/crash_core.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
> index 3426f6eef60b..5126a4fecb44 100644
> --- a/include/linux/crash_core.h
> +++ b/include/linux/crash_core.h
> @@ -131,7 +131,7 @@ static inline void __init reserve_crashkernel_generic(char *cmdline,
>  struct crash_mem {
>  	unsigned int max_nr_ranges;
>  	unsigned int nr_ranges;
> -	struct range ranges[];
> +	struct range ranges[] __counted_by(max_nr_ranges);

This __counted_by() only makes sense when there's a obvious upper
boundary, max_nr_ranges in this case. This heavily depends and isn't
much in kernel? E.g struct swap_info_struct->avail_lists[]. Just
curious, not related to this patch though.

>  };
>  
>  extern int crash_exclude_mem_range(struct crash_mem *mem,
> -- 
> 2.34.1
>