On Thu, May 07, 2020 at 07:01:06PM -0700, Peter Collingbourne wrote:

The kernel currently clears the tag bits (i.e. bits 56-63) in the fault
address exposed via siginfo.si_addr and sigcontext.fault_address. However,
the tag bits may be needed by tools in order to accurately diagnose
memory errors, such as HWASan [1] or future tools based on the Memory
Tagging Extension (MTE).

We should not stop clearing these bits in the existing fault address fields,
because there may be existing userspace applications that are expecting the tag
bits to be cleared. Instead, create a fault_addr_top_byte_context in sigcontext
(similar to the existing esr_context), and store the tag bits of FAR_EL1 there.

[1] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html

Signed-off-by: Peter Collingbourne <redacted>

It looks alright to me.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

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