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

Kees Cook
2024-07-08T19:18:41Z

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))

#define kmem_buckets_alloc(_b, _size, _flags) \
alloc_hooks(__kmalloc_node_noprof(PASS_BUCKET_PARAMS(_size, _b), _flags, NUMA_NO_NODE))
--
2.34.1