arm64: fix dump_instr when PAN and UAO are in use
If the kernel is set to show unhandled signals, and a user task does not handle a SIGILL as a result of an instruction abort, we will attempt to log the offending instruction with dump_instr before killing the task. We use dump_instr to log the encoding of the offending userspace instruction. However, dump_instr is also used to dump instructions from kernel space, and internally always switches to KERNEL_DS before dumping the instruction with get_user. When both PAN and UAO are in use, reading a user instruction via get_user while in KERNEL_DS will result in a permission fault, which leads to an Oops. As we have regs corresponding to the context of the original instruction abort, we can inspect this and only flip to KERNEL_DS if the original abort was taken from the kernel, avoiding this issue. At the same time, remove the redundant (and incorrect) comments regarding the order dump_mem and dump_instr are called in. Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: James Morse <james.morse@arm.com> Cc: Robin Murphy <robin.murphy@arm.com> Cc: <stable@vger.kernel.org> #4.6+ Signed-off-by: NMark Rutland <mark.rutland@arm.com> Reported-by: NVladimir Murzin <vladimir.murzin@arm.com> Tested-by: NVladimir Murzin <vladimir.murzin@arm.com> Fixes: 57f4959b ("arm64: kernel: Add support for User Access Override") Signed-off-by: NWill Deacon <will.deacon@arm.com>
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