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MIPS: relocatable: fix possible boot hangup with KASLR enabled

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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: 405bc8fd12 ("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>
This commit is contained in:
Alexander Lobakin 2021-01-10 14:21:05 +00:00 committed by Thomas Bogendoerfer
parent 6982224574
commit 69e976831c
1 changed files with 8 additions and 2 deletions
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10
arch/mips/kernel/relocate.c
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@ -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. */