4.16-stable review patch. If anyone has any objections, please let me know.
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From: Mark Rutland mark.rutland@arm.com
[ Upstream commit 4f74d72aa7067e75af92fbab077e6d7d0210be66 ]
When CONFIG_RANDOMIZE_TEXT_OFFSET=y, TEXT_OFFSET is an arbitrary multiple of PAGE_SIZE in the interval [0, 2MB).
The EFI stub does not account for the potential misalignment of TEXT_OFFSET relative to EFI_KIMG_ALIGN, and produces a randomized physical offset which is always a round multiple of EFI_KIMG_ALIGN. This may result in statically allocated objects whose alignment exceeds PAGE_SIZE to appear misaligned in memory. This has been observed to result in spurious stack overflow reports and failure to make use of the IRQ stacks, and theoretically could result in a number of other issues.
We can OR in the low bits of TEXT_OFFSET to ensure that we have the necessary offset (and hence preserve the misalignment of TEXT_OFFSET relative to EFI_KIMG_ALIGN), so let's do that.
Reported-by: Kim Phillips kim.phillips@arm.com Tested-by: Kim Phillips kim.phillips@arm.com [ardb: clarify comment and commit log, drop unneeded parens] Signed-off-by: Mark Rutland mark.rutland@arm.com Signed-off-by: Ard Biesheuvel ard.biesheuvel@linaro.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: linux-efi@vger.kernel.org Fixes: 6f26b3671184c36d ("arm64: kaslr: increase randomization granularity") Link: http://lkml.kernel.org/r/20180518140841.9731-2-ard.biesheuvel@linaro.org Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/firmware/efi/libstub/arm64-stub.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
--- a/drivers/firmware/efi/libstub/arm64-stub.c +++ b/drivers/firmware/efi/libstub/arm64-stub.c @@ -98,6 +98,16 @@ efi_status_t handle_kernel_image(efi_sys (phys_seed >> 32) & mask : TEXT_OFFSET;
/* + * With CONFIG_RANDOMIZE_TEXT_OFFSET=y, TEXT_OFFSET may not + * be a multiple of EFI_KIMG_ALIGN, and we must ensure that + * we preserve the misalignment of 'offset' relative to + * EFI_KIMG_ALIGN so that statically allocated objects whose + * alignment exceeds PAGE_SIZE appear correctly aligned in + * memory. + */ + offset |= TEXT_OFFSET % EFI_KIMG_ALIGN; + + /* * If KASLR is enabled, and we have some randomness available, * locate the kernel at a randomized offset in physical memory. */