LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Kees Cook <keescook@chromium.org>
To: Andrew Morton <akpm@linux-foundation.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: Thu, 19 Aug 2021 00:06:13 -0700	[thread overview]
Message-ID: <202108190003.37FF2F1D7@keescook> (raw)
In-Reply-To: <20210818161912.f14722707e06de1f046e948d@linux-foundation.org>

On Wed, Aug 18, 2021 at 04:19:12PM -0700, Andrew Morton wrote:
> 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

Oh, er, where did "Makefile: remove stale cc-option checks" go? Ah, I
see now:
https://lore.kernel.org/mm-commits/20210814215814.W_qqW%25akpm@linux-foundation.org/T/#u

Looks like I just happened to pick the wrong linux-next. ;)

Thanks for the fix-up!

-- 
Kees Cook

  reply	other threads:[~2021-08-19  7:06 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
2021-08-19  7:06     ` Kees Cook [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=202108190003.37FF2F1D7@keescook \
    --to=keescook@chromium.org \
    --cc=akpm@linux-foundation.org \
    --cc=apw@canonical.com \
    --cc=cl@linux.com \
    --cc=clang-built-linux@googlegroups.com \
    --cc=danielmicay@gmail.com \
    --cc=dennis@kernel.org \
    --cc=dwaipayanray1@gmail.com \
    --cc=iamjoonsoo.kim@lge.com \
    --cc=joe@perches.com \
    --cc=linux-hardening@vger.kernel.org \
    --cc=linux-kbuild@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=lukas.bulwahn@gmail.com \
    --cc=masahiroy@kernel.org \
    --cc=michal.lkml@markovi.net \
    --cc=nathan@kernel.org \
    --cc=ndesaulniers@google.com \
    --cc=ojeda@kernel.org \
    --cc=penberg@kernel.org \
    --cc=rientjes@google.com \
    --cc=tj@kernel.org \
    --cc=vbabka@suse.cz \
    --subject='Re: [PATCH v2 1/7] Compiler Attributes: Add __alloc_size() for better bounds checking' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).