linux-hardening - Re: [PATCH] compiler_types.h: Test for __alloc_size_

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Message-ID: <0eb638e3-b9ac-6dec-6881-b885c7874b45@suse.cz>
Date:   Thu, 29 Sep 2022 11:14:47 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Kees Cook <keescook@...omium.org>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yonghong Song <yhs@...com>, Hao Luo <haoluo@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] compiler_types.h: Test for __alloc_size__ again

On 9/29/22 10:16, Kees Cook wrote:
> While the "alloc_size" attribute is available on all GCC versions, I
> forgot that it gets disabled explicitly by the kernel in GCC < 9.1 due
> to misbehaviors. Add a note to the compiler_attributes.h entry for it,
> and restore the #ifdef in compiler_types.h.
> 
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Miguel Ojeda <ojeda@...nel.org>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Yonghong Song <yhs@...com>
> Cc: Hao Luo <haoluo@...gle.com>
> Cc: Marco Elver <elver@...gle.com>
> Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> Link: https://lore.kernel.org/lkml/CAMuHMdXK+UN1YVZm9DenuXAM8hZRUZJwp=SXsueP7sWiVU3a9A@mail.gmail.com
> Fixes: 63caa04ec60583b1 ("slab: Remove __malloc attribute from realloc functions")
> Signed-off-by: Kees Cook <keescook@...omium.org>

Thanks, I decided to late squash it so we don't needlessly cause issues for
people doing bisections with gcc-8 later.

> ---
> I swear I sent this earlier today, but I don't see it on lore still. Resending,
> so apologies if this is a duplicate.
> ---
>  include/linux/compiler_attributes.h | 3 ++-
>  include/linux/compiler_types.h      | 9 +++++++--
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
> index 465be5f072ff..55fbb6091ecf 100644
> --- a/include/linux/compiler_attributes.h
> +++ b/include/linux/compiler_attributes.h
> @@ -65,7 +65,8 @@
>  
>  /*
>   * Note: do not use this directly. Instead, use __alloc_size() since it is conditionally
> - * available and includes other attributes.
> + * available and includes other attributes. For GCC < 9.1, __alloc_size__ gets undefined
> + * in compiler-gcc.h, due to misbehaviors.
>   *
>   *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-alloc_005fsize-function-attribute
>   * clang: https://clang.llvm.org/docs/AttributeReference.html#alloc-size
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index f141a6f6b9f6..0717534f8364 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -275,8 +275,13 @@ struct ftrace_likely_data {
>   * be performing a _reallocation_, as that may alias the existing pointer.
>   * For these, use __realloc_size().
>   */
> -#define __alloc_size(x, ...)	__alloc_size__(x, ## __VA_ARGS__) __malloc
> -#define __realloc_size(x, ...)	__alloc_size__(x, ## __VA_ARGS__)
> +#ifdef __alloc_size__
> +# define __alloc_size(x, ...)	__alloc_size__(x, ## __VA_ARGS__) __malloc
> +# define __realloc_size(x, ...)	__alloc_size__(x, ## __VA_ARGS__)
> +#else
> +# define __alloc_size(x, ...)	__malloc
> +# define __realloc_size(x, ...)
> +#endif
>  
>  #ifndef asm_volatile_goto
>  #define asm_volatile_goto(x...) asm goto(x)