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

[Kees Cook <kees@kernel.org>]

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