Compiler Attributes: Add __alloc_size for better bounds checking fix

Adjust the warning logic to deal with pre-9.1 gcc behaviors.

Link: https://lkml.kernel.org/r/20210827151327.2729736-1-keescook@chromium.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

diff --git a/Makefile b/Makefile
index 56151c396958025a59c8d6035b3d75e728f992f8..730d42641857f0622d524b8b6198ff4634244e1e 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -1099,8 +1099,17 @@ endif
 
 ifdef CONFIG_CC_IS_GCC
 # The allocators already balk at large sizes, so silence the compiler
-# warnings for bounds checks involving those possible values.
-KBUILD_CFLAGS += -Wno-alloc-size-larger-than
+# warnings for bounds checks involving those possible values. While
+# -Wno-alloc-size-larger-than would normally be used here, earlier versions
+# of gcc (<9.1) weirdly don't handle the option correctly when _other_
+# warnings are produced (?!). Using -Walloc-size-larger-than=SIZE_MAX
+# doesn't work (as it is documented to), silently resolving to "0" prior to
+# version 9.1 (and producing an error more recently). Numeric values larger
+# than PTRDIFF_MAX also don't work prior to version 9.1, which are silently
+# ignored, continuing to default to PTRDIFF_MAX. So, left with no other
+# choice, we must perform a versioned check to disable this warning.
+# https://lore.kernel.org/lkml/20210824115859.187f272f@canb.auug.org.au
+KBUILD_CFLAGS += $(call cc-ifversion, -ge, 0901, -Wno-alloc-size-larger-than)
 endif
 
 # disable invalid "can't wrap" optimizations for signed / pointers