arm64: mm: abort uaccess retries upon fatal signal

commit 289d07a2dc6c6b6f3e4b8a62669320d99dbe6c3d upstream.

When there's a fatal signal pending, arm64's do_page_fault()
implementation returns 0. The intent is that we'll return to the
faulting userspace instruction, delivering the signal on the way.

However, if we take a fatal signal during fixing up a uaccess, this
results in a return to the faulting kernel instruction, which will be
instantly retried, resulting in the same fault being taken forever. As
the task never reaches userspace, the signal is not delivered, and the
task is left unkillable. While the task is stuck in this state, it can
inhibit the forward progress of the system.

To avoid this, we must ensure that when a fatal signal is pending, we
apply any necessary fixup for a faulting kernel instruction. Thus we
will return to an error path, and it is up to that code to make forward
progress towards delivering the fatal signal.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Laura Abbott <labbott@redhat.com>
Reviewed-by: Steve Capper <steve.capper@arm.com>
Tested-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: James Morse <james.morse@arm.com>
Tested-by: James Morse <james.morse@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 37b95dff0b07f4eb0967c4a9b27318c6d81daa8c..3952d5ef8a7a34eb42543e800e5c4c09a3644552 100644 (file)
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -397,8 +397,11 @@ retry:
         * signal first. We do not need to release the mmap_sem because it
         * would already be released in __lock_page_or_retry in mm/filemap.c.
         */
-       if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
+       if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) {
+               if (!user_mode(regs))
+                       goto no_context;
                return 0;
+       }
 
        /*
         * Major/minor page fault accounting is only done on the initial