Compiler Attributes: add __alloc_size() for better bounds checking

GCC and Clang can use the "alloc_size" attribute to better inform the
results of __builtin_object_size() (for compile-time constant values).
Clang can additionally use alloc_size to inform the results of
__builtin_dynamic_object_size() (for run-time values).

Because GCC sees the frequent use of struct_size() as an allocator size
argument, and notices it can return SIZE_MAX (the overflow indication),
it complains about these call sites overflowing (since SIZE_MAX is
greater than the default -Walloc-size-larger-than=PTRDIFF_MAX).  This
isn't helpful since we already know a SIZE_MAX will be caught at
run-time (this was an intentional design).  To deal with this, we must
disable this check as it is both a false positive and redundant.  (Clang
does not have this warning option.)

Unfortunately, just checking the -Wno-alloc-size-larger-than is not
sufficient to make the __alloc_size attribute behave correctly under
older GCC versions.  The attribute itself must be disabled in those
situations too, as there appears to be no way to reliably silence the
SIZE_MAX constant expression cases for GCC versions less than 9.1:

   In file included from ./include/linux/resource_ext.h:11,
                    from ./include/linux/pci.h:40,
                    from drivers/net/ethernet/intel/ixgbe/ixgbe.h:9,
                    from drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c:4:
   In function 'kmalloc_node',
       inlined from 'ixgbe_alloc_q_vector' at ./include/linux/slab.h:743:9:
   ./include/linux/slab.h:618:9: error: argument 1 value '18446744073709551615' exceeds maximum object size 9223372036854775807 [-Werror=alloc-size-larger-than=]
     return __kmalloc_node(size, flags, node);
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   ./include/linux/slab.h: In function 'ixgbe_alloc_q_vector':
   ./include/linux/slab.h:455:7: note: in a call to allocation function '__kmalloc_node' declared here
    void *__kmalloc_node(size_t size, gfp_t flags, int node) __assume_slab_alignment __malloc;
          ^~~~~~~~~~~~~~

Specifically:
 '-Wno-alloc-size-larger-than' is not correctly handled by GCC < 9.1
    https://godbolt.org/z/hqsfG7q84 (doesn't disable)
    https://godbolt.org/z/P9jdrPTYh (doesn't admit to not knowing about option)
    https://godbolt.org/z/465TPMWKb (only warns when other warnings appear)

 '-Walloc-size-larger-than=18446744073709551615' is not handled by GCC < 8.2
    https://godbolt.org/z/73hh1EPxz (ignores numeric value)

Since anything marked with __alloc_size would also qualify for marking
with __malloc, just include __malloc along with it to avoid redundant
markings.  (Suggested by Linus Torvalds.)

Finally, make sure checkpatch.pl doesn't get confused about finding the
__alloc_size attribute on functions.  (Thanks to Joe Perches.)

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Kees Cook <[email protected]>
Tested-by: Randy Dunlap <[email protected]>
Cc: Andy Whitcroft <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Daniel Micay <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Dennis Zhou <[email protected]>
Cc: Dwaipayan Ray <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Lukas Bulwahn <[email protected]>
Cc: Pekka Enberg <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Alexandre Bounine <[email protected]>
Cc: Gustavo A. R. Silva <[email protected]>
Cc: Ira Weiny <[email protected]>
Cc: Jing Xiangfeng <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: kernel test robot <[email protected]>
Cc: Matt Porter <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Nick Desaulniers <[email protected]>
Cc: Souptick Joarder <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 2 insertions, 1 deletions

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index c27d2312cfc3..88cb294dc447 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*\(\s*\d+\s*(?:,\s*\d+\s*)?\)
 		  }x;
 our $Modifier;
 our $Inline	= qr{inline|__always_inline|noinline|__inline|__inline__};