From: Alexander Lobakin alobakin@pm.me
commit 69e976831cd53f9ba304fd20305b2025ecc78eab upstream.
LLVM-built Linux triggered a boot hangup with KASLR enabled.
arch/mips/kernel/relocate.c:get_random_boot() uses linux_banner, which is a string constant, as a random seed, but accesses it as an array of unsigned long (in rotate_xor()). When the address of linux_banner is not aligned to sizeof(long), such access emits unaligned access exception and hangs the kernel.
Use PTR_ALIGN() to align input address to sizeof(long) and also align down the input length to prevent possible access-beyond-end.
Fixes: 405bc8fd12f5 ("MIPS: Kernel: Implement KASLR using CONFIG_RELOCATABLE") Cc: stable@vger.kernel.org # 4.7+ Signed-off-by: Alexander Lobakin alobakin@pm.me Tested-by: Nathan Chancellor natechancellor@gmail.com Reviewed-by: Kees Cook keescook@chromium.org Signed-off-by: Thomas Bogendoerfer tsbogend@alpha.franken.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/mips/kernel/relocate.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)
--- a/arch/mips/kernel/relocate.c +++ b/arch/mips/kernel/relocate.c @@ -175,8 +175,14 @@ static int __init relocate_exception_tab static inline __init unsigned long rotate_xor(unsigned long hash, const void *area, size_t size) { - size_t i; - unsigned long *ptr = (unsigned long *)area; + const typeof(hash) *ptr = PTR_ALIGN(area, sizeof(hash)); + size_t diff, i; + + diff = (void *)ptr - area; + if (unlikely(size < diff + sizeof(hash))) + return hash; + + size = ALIGN_DOWN(size - diff, sizeof(hash));
for (i = 0; i < size / sizeof(hash); i++) { /* Rotate by odd number of bits and XOR. */