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arm64: only advance singlestep for user instruction traps

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Our arm64_skip_faulting_instruction() helper advances the userspace
singlestep state machine, but this is also called by the kernel BRK
handler, as used for WARN*().

Thus, if we happen to hit a WARN*() while the user singlestep state
machine is in the active-no-pending state, we'll advance to the
active-pending state without having executed a user instruction, and
will take a step exception earlier than expected when we return to
userspace.

Let's fix this by only advancing the state machine when skipping a user
instruction.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Mark Rutland 2018-04-03 11:22:51 +01:00 committed by Will Deacon
parent ed231ae384
commit 9478f1927e
1 changed files with 2 additions and 1 deletions
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3
arch/arm64/kernel/traps.c
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@ -277,7 +277,8 @@ void arm64_skip_faulting_instruction(struct pt_regs *regs, unsigned long size)
* If we were single stepping, we want to get the step exception after
* we return from the trap.
*/
user_fastforward_single_step(current);
if (user_mode(regs))
user_fastforward_single_step(current);
}
static LIST_HEAD(undef_hook);