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From: Andrew Morton <akpm@linux-foundation.org>
To: Kees Cook <keescook@chromium.org>
Cc: linux-kernel@vger.kernel.org, Miguel Ojeda <ojeda@kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	clang-built-linux@googlegroups.com, Joe Perches <joe@perches.com>,
	Andy Whitcroft <apw@canonical.com>,
	Dwaipayan Ray <dwaipayanray1@gmail.com>,
	Lukas Bulwahn <lukas.bulwahn@gmail.com>,
	Christoph Lameter <cl@linux.com>,
	Pekka Enberg <penberg@kernel.org>,
	David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Daniel Micay <danielmicay@gmail.com>,
	Dennis Zhou <dennis@kernel.org>, Tejun Heo <tj@kernel.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Michal Marek <michal.lkml@markovi.net>,
	linux-mm@kvack.org, linux-kbuild@vger.kernel.org,
	linux-hardening@vger.kernel.org
Subject: Re: [PATCH v2 1/7] Compiler Attributes: Add __alloc_size() for better bounds checking
Date: Wed, 18 Aug 2021 16:19:12 -0700	[thread overview]
Message-ID: <20210818161912.f14722707e06de1f046e948d@linux-foundation.org> (raw)
In-Reply-To: <20210818214021.2476230-2-keescook@chromium.org>

On Wed, 18 Aug 2021 14:40:15 -0700 Kees Cook <keescook@chromium.org> wrote:

> GCC and Clang can use the "alloc_size" attribute to better inform the
> results of __builtin_object_size() (for compile-time constant values).
> Clang can additionally use alloc_size to inform the results of
> __builtin_dynamic_object_size() (for run-time values).
> 
> Because GCC sees the frequent use of struct_size() as an allocator size
> argument, and notices it can return SIZE_MAX (the overflow indication),
> it complains about these call sites may overflow (since SIZE_MAX is
> greater than the default -Walloc-size-larger-than=PTRDIFF_MAX). This
> isn't helpful since we already know a SIZE_MAX will be caught at run-time
> (this was an intentional design). Instead, just disable this check as
> it is both a false positive and redundant. (Clang does not have this
> warning option.)
> 
> ...
>
> --- a/Makefile
> +++ b/Makefile
> @@ -1078,9 +1078,13 @@ KBUILD_CFLAGS += $(call cc-disable-warning, stringop-overflow)
>  # Another good warning that we'll want to enable eventually
>  KBUILD_CFLAGS += $(call cc-disable-warning, restrict)
>  
> -# Enabled with W=2, disabled by default as noisy
>  ifdef CONFIG_CC_IS_GCC
> +# Enabled with W=2, disabled by default as noisy
>  KBUILD_CFLAGS += -Wno-maybe-uninitialized
> +
> +# The allocators already balk at large sizes, so silence the compiler
> +# warnings for bounds checks involving those possible values.
> +KBUILD_CFLAGS += -Wno-alloc-size-larger-than
>  endif
>  
>  # disable invalid "can't wrap" optimizations for signed / pointers

Makefile has changed.  I did this:

--- a/Makefile~compiler-attributes-add-__alloc_size-for-better-bounds-checking
+++ a/Makefile
@@ -1003,6 +1003,12 @@ KBUILD_CFLAGS += $(call cc-disable-warni
 # Enabled with W=2, disabled by default as noisy
 KBUILD_CFLAGS += $(call cc-disable-warning, maybe-uninitialized)
 
+ifdef CONFIG_CC_IS_GCC
+# The allocators already balk at large sizes, so silence the compiler
+# warnings for bounds checks involving those possible values.
+KBUILD_CFLAGS += -Wno-alloc-size-larger-than
+endif
+
 # disable invalid "can't wrap" optimizations for signed / pointers
 KBUILD_CFLAGS	+= -fno-strict-overflow
 
_


  parent reply	other threads:[~2021-08-18 23:19 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-18 21:40 [PATCH v2 0/7] " Kees Cook
2021-08-18 21:40 ` [PATCH v2 1/7] Compiler Attributes: " Kees Cook
2021-08-18 21:51   ` Nathan Chancellor
2021-08-18 23:19   ` Andrew Morton [this message]
2021-08-19  7:06     ` Kees Cook
2021-08-19  0:04   ` Miguel Ojeda
2021-08-18 21:40 ` [PATCH v2 2/7] checkpatch: Add __alloc_size() to known $Attribute Kees Cook
2021-08-18 21:40 ` [PATCH v2 3/7] slab: Clean up function declarations Kees Cook
2021-08-18 21:40 ` [PATCH v2 4/7] slab: Add __alloc_size attributes for better bounds checking Kees Cook
2021-08-19  8:27   ` Rasmus Villemoes
2021-08-25 21:31   ` Nick Desaulniers
2021-09-22 22:41     ` Kees Cook
2021-08-18 21:40 ` [PATCH v2 5/7] mm/page_alloc: " Kees Cook
2021-08-18 21:40 ` [PATCH v2 6/7] percpu: " Kees Cook
2021-08-19  0:42   ` Dennis Zhou
2021-08-19  3:36     ` Kees Cook
2021-08-19 14:12       ` Dennis Zhou
2021-08-20  5:11   ` Andrew Morton
2021-08-20  5:27     ` Kees Cook
2021-08-18 21:40 ` [PATCH v2 7/7] mm/vmalloc: " Kees Cook

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