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[RFC,2/4] slab: Detect negative size values and saturate

Message ID 20240708191840.335463-2-kees@kernel.org (mailing list archive)
State Handled Elsewhere
Headers show
Series slab: Allow for type introspection during allocation | expand

Commit Message

Kees Cook July 8, 2024, 7:18 p.m. UTC 
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@kernel.org>
---
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: linux-mm@kvack.org
---
 include/linux/slab.h | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

Comments

Przemek Kitszel July 9, 2024, 6:57 a.m. UTC | #1 
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@kernel.org>
> ---
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Pekka Enberg <penberg@kernel.org>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: Roman Gushchin <roman.gushchin@linux.dev>
> Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> Cc: linux-mm@kvack.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!

What about bool?
What about long long?
(by this commit one will get a rather easy to parse compile error, but
the next one will obscure it a bit)

Consider the following correct (albeit somewhat weird) code:
	/* header */
	char *state;

	/* .c impl, init part */
	bool needs_state = some_expr();
	state = kmalloc(needs_state, GFP_KERNEL);

	/* .c, other part */
	if (ZERO_OR_NULL_PTR(state))
		return _EARLY;
	*state = state_machine_action(*state);

>   
>   #define kmem_buckets_alloc(_b, _size, _flags)	\
>   	alloc_hooks(__kmalloc_node_noprof(PASS_BUCKET_PARAMS(_size, _b), _flags, NUMA_NO_NODE))
Kees Cook July 9, 2024, 4:09 p.m. UTC | #2 
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@kernel.org>
> > ---
> > Cc: Christoph Lameter <cl@linux.com>
> > Cc: Pekka Enberg <penberg@kernel.org>
> > Cc: David Rientjes <rientjes@google.com>
> > Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Cc: Roman Gushchin <roman.gushchin@linux.dev>
> > Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> > Cc: linux-mm@kvack.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/
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Patch

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))
 
 #define kmem_buckets_alloc(_b, _size, _flags)	\
 	alloc_hooks(__kmalloc_node_noprof(PASS_BUCKET_PARAMS(_size, _b), _flags, NUMA_NO_NODE))