linux-hardening - Re: [PATCH 2/5] slab: Add __alloc_size attributes for better bounds checking

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Date:   Tue, 17 Aug 2021 22:31:32 -0700
From:   Joe Perches <joe@...ches.com>
To:     Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Cc:     Daniel Micay <danielmicay@...il.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>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        Miguel Ojeda <ojeda@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        clang-built-linux@...glegroups.com, linux-kbuild@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH 2/5] slab: Add __alloc_size attributes for better bounds
 checking

On Tue, 2021-08-17 at 22:08 -0700, Kees Cook wrote:
> As already done in GrapheneOS, add the __alloc_size attribute for
> regular kmalloc interfaces, to provide additional hinting for better
> bounds checking, assisting CONFIG_FORTIFY_SOURCE and other compiler
> optimizations.
[]
> diff --git a/include/linux/slab.h b/include/linux/slab.h
[]
> @@ -181,7 +181,7 @@ int kmem_cache_shrink(struct kmem_cache *);
>  /*
>   * Common kmalloc functions provided by all allocators
>   */
> -void * __must_check krealloc(const void *, size_t, gfp_t);
> +void * __must_check krealloc(const void *, size_t, gfp_t) __alloc_size(2);

I suggest the __alloc_size attribute be placed at the beginning of the
function declaration to be more similar to the common __printf attribute
location uses.

__alloc_size(2)
void * __must_check krealloc(const void *, size_t, gfp_t);

I really prefer the __must_check to be with the other attribute and that
function declarations have argument names too like:

__alloc_size(2) __must_check
void *krealloc(const void *ptr, size_t size, gfp_t gfp);

but there are a _lot_ of placement of __must_check after the return type

Lastly __alloc_size should probably be added to checkpatch

Maybe:
---
 scripts/checkpatch.pl | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 161ce7fe5d1e5..1a166b5cf3447 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -489,7 +489,8 @@ our $Attribute	= qr{
 			____cacheline_aligned|
 			____cacheline_aligned_in_smp|
 			____cacheline_internodealigned_in_smp|
-			__weak
+			__weak|
+			__alloc_size\s*\(\s*\d+\s*(?:,\s*d+\s*){0,5}\)
 		  }x;
 our $Modifier;
 our $Inline	= qr{inline|__always_inline|noinline|__inline|__inline__};