linux-kernel - Re: [PATCH] slab: remove __alloc_size attribute from __kmalloc_track

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Date:   Fri, 18 Feb 2022 18:14:55 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     stable <stable@...r.kernel.org>, Kees Cook <keescook@...omium.org>,
        Daniel Micay <danielmicay@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Chancellor <nathan@...nel.org>, linux-mm@...ck.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] slab: remove __alloc_size attribute from
 __kmalloc_track_caller

On 2/18/22 14:13, Greg Kroah-Hartman wrote:
> Commit c37495d6254c ("slab: add __alloc_size attributes for better
> bounds checking") added __alloc_size attributes to a bunch of kmalloc
> function prototypes.  Unfortunately the change to __kmalloc_track_caller
> seems to cause clang to generate broken code and the first time this is
> called when booting, the box will crash.
> 
> While the compiler problems are being reworked and attempted to be
> solved, let's just drop the attribute to solve the issue now.  Once it
> is resolved it can be added back.

Could we instead wrap it in some #ifdef that' only true for clang build?
That would make the workaround more precise and self-documented. Even
better if it can trigger using clang version range and once a fixed
clang version is here, it can be updated to stay true for older clangs.

> Fixes: c37495d6254c ("slab: add __alloc_size attributes for better bounds checking")
> Cc: stable <stable@...r.kernel.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Daniel Micay <danielmicay@...il.com>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Pekka Enberg <penberg@...nel.org>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Nathan Chancellor <nathan@...nel.org>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> Cc: llvm@...ts.linux.dev
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  include/linux/slab.h | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 37bde99b74af..5b6193fd8bd9 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -660,8 +660,7 @@ static inline __alloc_size(1, 2) void *kcalloc(size_t n, size_t size, gfp_t flag
>   * allocator where we care about the real place the memory allocation
>   * request comes from.
>   */
> -extern void *__kmalloc_track_caller(size_t size, gfp_t flags, unsigned long caller)
> -				   __alloc_size(1);
> +extern void *__kmalloc_track_caller(size_t size, gfp_t flags, unsigned long caller);
>  #define kmalloc_track_caller(size, flags) \
>  	__kmalloc_track_caller(size, flags, _RET_IP_)
>