linux-kernel - Re: [RFC][PATCH 2/4] slab: Detect negative size values and saturate

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Message-ID: <202407090903.38C2F463@keescook>
Date: Tue, 9 Jul 2024 09:09:57 -0700
From: Kees Cook <kees@...nel.org>
To: Przemek Kitszel <przemyslaw.kitszel@...el.com>
Cc: Vlastimil Babka <vbabka@...e.cz>, 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>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org,
	Jann Horn <jannh@...gle.com>, Tony Luck <tony.luck@...el.com>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Miguel Ojeda <ojeda@...nel.org>, Marco Elver <elver@...gle.com>,
	Nathan Chancellor <nathan@...nel.org>, Hao Luo <haoluo@...gle.com>,
	"Guilherme G. Piccoli" <gpiccoli@...lia.com>,
	Mark Rutland <mark.rutland@....com>,
	Jakub Kicinski <kuba@...nel.org>, Petr Pavlu <petr.pavlu@...e.com>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	Tony Ambardar <tony.ambardar@...il.com>,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [RFC][PATCH 2/4] slab: Detect negative size values and saturate

On Tue, Jul 09, 2024 at 08:57:55AM +0200, Przemek Kitszel wrote:
> On 7/8/24 21:18, Kees Cook wrote:
> > The allocator will already reject giant sizes seen from negative size
> > arguments, so this commit mainly services as an example for initial
> > type-based filtering. The size argument is checked for negative values
> > in signed arguments, saturating any if found instead of passing them on.
> > 
> > For example, now the size is checked:
> > 
> > Before:
> > 				/* %rdi unchecked */
> >   1eb:   be c0 0c 00 00          mov    $0xcc0,%esi
> >   1f0:   e8 00 00 00 00          call   1f5 <do_SLAB_NEGATIVE+0x15>
> >                          1f1: R_X86_64_PLT32 __kmalloc_noprof-0x4
> > 
> > After:
> >   6d0:   48 63 c7                movslq %edi,%rax
> >   6d3:   85 ff                   test   %edi,%edi
> >   6d5:   be c0 0c 00 00          mov    $0xcc0,%esi
> >   6da:   48 c7 c2 ff ff ff ff    mov    $0xffffffffffffffff,%rdx
> >   6e1:   48 0f 49 d0             cmovns %rax,%rdx
> >   6e5:   48 89 d7                mov    %rdx,%rdi
> >   6e8:   e8 00 00 00 00          call   6ed <do_SLAB_NEGATIVE+0x1d>
> >                          6e9: R_X86_64_PLT32     __kmalloc_noprof-0x4
> > 
> > Signed-off-by: Kees Cook <kees@...nel.org>
> > ---
> > Cc: Christoph Lameter <cl@...ux.com>
> > Cc: Pekka Enberg <penberg@...nel.org>
> > Cc: David Rientjes <rientjes@...gle.com>
> > Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Vlastimil Babka <vbabka@...e.cz>
> > Cc: Roman Gushchin <roman.gushchin@...ux.dev>
> > Cc: Hyeonggon Yoo <42.hyeyoo@...il.com>
> > Cc: linux-mm@...ck.org
> > ---
> >   include/linux/slab.h | 19 ++++++++++++++++++-
> >   1 file changed, 18 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index d99afce36098..7353756cbec6 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -684,7 +684,24 @@ static __always_inline __alloc_size(1) void *kmalloc_noprof(size_t size, gfp_t f
> >   	}
> >   	return __kmalloc_noprof(size, flags);
> >   }
> > -#define kmalloc(...)				alloc_hooks(kmalloc_noprof(__VA_ARGS__))
> > +#define kmalloc_sized(...)			alloc_hooks(kmalloc_noprof(__VA_ARGS__))
> > +
> > +#define __size_force_positive(x)				\
> > +	({							\
> > +		typeof(__force_integral_expr(x)) __forced_val =	\
> > +			__force_integral_expr(x);		\
> > +		__forced_val < 0 ? SIZE_MAX : __forced_val;	\
> > +	})
> > +
> > +#define kmalloc(p, gfp)		_Generic((p),    \
> > +	unsigned char:  kmalloc_sized(__force_integral_expr(p), gfp), \
> > +	unsigned short: kmalloc_sized(__force_integral_expr(p), gfp), \
> > +	unsigned int:   kmalloc_sized(__force_integral_expr(p), gfp), \
> > +	unsigned long:  kmalloc_sized(__force_integral_expr(p), gfp), \
> > +	signed char:    kmalloc_sized(__size_force_positive(p), gfp), \
> > +	signed short:   kmalloc_sized(__size_force_positive(p), gfp), \
> > +	signed int:     kmalloc_sized(__size_force_positive(p), gfp), \
> > +	signed long:    kmalloc_sized(__size_force_positive(p), gfp))
> 
> I like this idea and series very much, thank you!

Thanks!

> What about bool?
> What about long long?

Ah yes, I will add these. LKP also found a weird one (a bitfield!) that
I'm fixing at the source:
https://lore.kernel.org/lkml/20240709154953.work.953-kees@kernel.org/

-- 
Kees Cook