From: Nathan Chancellor <nathan@kernel.org>
To: Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org
Cc: Miguel Ojeda <ojeda@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
clang-built-linux@googlegroups.com,
Andrew Morton <akpm@linux-foundation.org>,
Daniel Micay <danielmicay@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>, 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 1/5] Compiler Attributes: Add __alloc_size() for better bounds checking
Date: Wed, 18 Aug 2021 11:04:32 -0700 [thread overview]
Message-ID: <d326fbfc-dc96-b6e9-6fd8-31df3eb9f1cb@kernel.org> (raw)
In-Reply-To: <20210818050841.2226600-2-keescook@chromium.org>
On 8/17/2021 10:08 PM, Kees Cook 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 informt the results of
> __builtin_dynamic_object_size() (for run-time values).
>
> Additionally disables -Wno-alloc-size-larger-than since the allocators
> already reject SIZE_MAX, and the compile-time warnings aren't helpful.
In addition to what Miguel said, it might be helpful to mention that
this warning is GCC specific, I was a little confused at first as to why
it was just being added in the GCC only block :)
Otherwise, the attribute addition looks good to me. I will add my tag on v2.
> Cc: Miguel Ojeda <ojeda@kernel.org>
> Cc: Nathan Chancellor <nathan@kernel.org>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: clang-built-linux@googlegroups.com
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> Makefile | 6 +++++-
> include/linux/compiler_attributes.h | 6 ++++++
> 2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index 1b238ce86ed4..3b6fb740584e 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1076,9 +1076,13 @@ 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
> diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
> index 67c5667f8042..203b0ac62d15 100644
> --- a/include/linux/compiler_attributes.h
> +++ b/include/linux/compiler_attributes.h
> @@ -54,6 +54,12 @@
> #define __aligned(x) __attribute__((__aligned__(x)))
> #define __aligned_largest __attribute__((__aligned__))
>
> +/*
> + * 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
> + */
> +#define __alloc_size(x, ...) __attribute__((__alloc_size__(x, ## __VA_ARGS__)))
> +
> /*
> * Note: users of __always_inline currently do not write "inline" themselves,
> * which seems to be required by gcc to apply the attribute according
>
next prev parent reply other threads:[~2021-08-18 18:04 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-18 5:08 [PATCH 0/5] Add __alloc_size() for better bounds checking Kees Cook
2021-08-18 5:08 ` [PATCH 1/5] Compiler Attributes: " Kees Cook
2021-08-18 13:07 ` Miguel Ojeda
2021-08-18 17:58 ` Kees Cook
2021-08-18 18:04 ` Nathan Chancellor [this message]
2021-08-18 21:04 ` Kees Cook
2021-08-18 5:08 ` [PATCH 2/5] slab: Add __alloc_size attributes " Kees Cook
2021-08-18 5:31 ` Joe Perches
2021-08-18 6:16 ` Kees Cook
2021-08-18 6:30 ` Joe Perches
2021-08-19 0:27 ` Matthew Wilcox
2021-08-19 1:10 ` Joe Perches
2021-08-19 2:16 ` Matthew Wilcox
2021-08-19 2:59 ` Joe Perches
2021-08-18 5:08 ` [PATCH 3/5] mm/page_alloc: " Kees Cook
2021-08-18 5:08 ` [PATCH 4/5] percpu: " Kees Cook
2021-08-18 5:08 ` [PATCH 5/5] mm/vmalloc: " Kees Cook
2021-08-19 9:09 ` [PATCH 0/5] Add __alloc_size() " Christoph Hellwig
2021-08-19 14:18 ` Daniel Micay
2021-08-25 10:01 ` Christoph Lameter
2021-08-25 16:34 ` Kees Cook
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