arm64: only advance singlestep for user instruction traps

BugLink: http://bugs.launchpad.net/bugs/1794889
[ Upstream commit 9478f1927e6ef9ef5e1ad761af1c98aa8e40b7f5 ]

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>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index eb2d15147e8d3bb2be8731400990f18979022fce..e904f4ed49ff302363ee89df0dbb1d3520262dda 100644 (file)
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -243,7 +243,8 @@ 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);