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Testing the fortified string functions[1] would cause a kernel panic on boot in test_feature_fixups() due to a buffer overflow in memcmp. This boils down to things like this: extern unsigned int ftr_fixup_test1; extern unsigned int ftr_fixup_test1_orig; check(memcmp(&ftr_fixup_test1, &ftr_fixup_test1_orig, size) == 0); We know that these are asm labels so it is safe to read up to 'size' bytes at those addresses. However, because we have passed the address of a single unsigned int to memcmp, the compiler believes the underlying object is in fact a single unsigned int. So if size > sizeof(unsigned int), there will be a panic at runtime. We can fix this by changing the types: instead of calling the asm labels unsigned ints, call them unsigned int[]s. Therefore the size isn't incorrectly determined at compile time and we get a regular unsafe memcmp and no panic. [1] http://openwall.com/lists/kernel-hardening/2017/05/09/2 Link: http://lkml.kernel.org/r/1497903987-21002-7-git-send-email-keescook@chromium.org Signed-off-by: Daniel Axtens <dja@axtens.net> Signed-off-by: Kees Cook <keescook@chromium.org> Suggested-by: Michael Ellerman <mpe@ellerman.id.au> Tested-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com> Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com> Cc: Kees Cook <keescook@chromium.org> Cc: Daniel Micay <danielmicay@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.