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

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Date:   Tue, 17 Aug 2021 23:30:52 -0700
From:   Joe Perches <joe@...ches.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org, 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 23:16 -0700, Kees Cook wrote:
> On Tue, Aug 17, 2021 at 10:31:32PM -0700, Joe Perches wrote:
> > 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.
[]
> > Lastly __alloc_size should probably be added to checkpatch
> 
> Oh, yes! Thanks for the reminder.
> 
> > 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*\(\s*\d+\s*(?:,\s*d+\s*){0,5}\)
> 
> Why the "{0,5}" bit here? I was expecting just "?". (i.e. it can have
> either 1 or 2 arguments.)

You are right.  I misread the doc.  I also missed a \ before the last d.

So that last added line should maybe be: (totally untested btw)

+			__alloc_size\s*\(\s*\d+\s*(?:,\s*\d+\s*)?\)