arm64: only advance singlestep for user instruction traps

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>

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 1cb2749a72bfed65cd33d3a24695ddef2bbce517..8bbdc17e49df79cab3e8576783216e91aef6c746 100644 (file)
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -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);