Re: [PATCH mips-fixes] MIPS: relocatable: fix possible boot hangup with KASLR enabled
From: Nathan Chancellor <hidden>
Date: 2021-01-11 05:22:46
Also in:
lkml, stable
On Sun, Jan 10, 2021 at 02:21:05PM +0000, Alexander Lobakin wrote:
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 <redacted>Apologies for not being familiar enough with the issue to give a review but I did reproduce the hang that the commit mentions with malta_kvm_guest_defconfig + CONFIG_RELOCATABLE=y + CONFIG_RANDOMIZE_BASE=y and this patch does resolve it so: Tested-by: Nathan Chancellor <redacted>
quoted hunk ↗ jump to hunk
--- arch/mips/kernel/relocate.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)diff --git a/arch/mips/kernel/relocate.c b/arch/mips/kernel/relocate.c index 47aeb3350a76..0e365b7c742d 100644 --- a/arch/mips/kernel/relocate.c +++ b/arch/mips/kernel/relocate.c@@ -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. */-- 2.30.0