[PATCH 1/2] arm64: fix dump_instr when PAN and UAO are in use

[mark.rutland@arm.com (Mark Rutland)]

On Mon, Jun 13, 2016 at 01:48:24PM +0100, Will Deacon wrote:
> On Mon, Jun 13, 2016 at 11:15:14AM +0100, Mark Rutland wrote:
> > 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.
> > 
> > Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> > Reported-by: Vladimir Murzin <vladimir.murzin@arm.com>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: James Morse <james.morse@arm.com>
> > Cc: Robin Murphy <robin.murphy@arm.com>
> > Cc: Will Deacon <will.deacon@arm.com>
> > Fixes: 57f4959bad0a154a ("arm64: kernel: Add support for User Access Override")
> > ---
> >  arch/arm64/kernel/traps.c | 26 +++++++++++++-------------
> >  1 file changed, 13 insertions(+), 13 deletions(-)
> 
> Queued as a fix for 4.8 w/ Vladimir's Tested-by. Please try to keep fixes
> and cleanups/features separate in future series.

Cheers, will do.

I assume you've only taken patch 1, and it's up to Catalin to take patch
2 for v4.8. I'll poke as necessary for that to happen.

Thanks,
Mark.