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Commit f7a97dc3 authored by Alexander Lobakin's avatar Alexander Lobakin Committed by Greg Kroah-Hartman
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MIPS: relocatable: fix possible boot hangup with KASLR enabled 



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: 405bc8fd ("MIPS: Kernel: Implement KASLR using CONFIG_RELOCATABLE")
Cc: stable@vger.kernel.org # 4.7+
Signed-off-by: default avatarAlexander Lobakin <alobakin@pm.me>
Tested-by: default avatarNathan Chancellor <natechancellor@gmail.com>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarThomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent f5c2f797

arch/mips/kernel/relocate.c

+8 −2
Original line number Diff line number Diff line
@@ -187,8 +187,14 @@ static int __init relocate_exception_table(long offset) 
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. */