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
_
next prev 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] Add __alloc_size() for better bounds checking 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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