[PATCH 5.10 063/126] xtensa: fix uaccess-related livelock in do_page_fault

Greg Kroah-Hartman
2021-04-05T09:11:34Z

From: Max Filippov <jcmvbkbc@gmail.com>

commit 7b9acbb6aad4f54623dcd4bd4b1a60fe0c727b09 upstream.

If a uaccess (e.g. get_user()) triggers a fault and there's a
fault signal pending, the handler will return to the uaccess without
having performed a uaccess fault fixup, and so the CPU will immediately
execute the uaccess instruction again, whereupon it will livelock
bouncing between that instruction and the fault handler.

https://lore.kernel.org/lkml/20210121123140.GD48431@C02TD0UTHF1T.local/

Cc: stable@vger.kernel.org
Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/xtensa/mm/fault.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

--- a/arch/xtensa/mm/fault.c
+++ b/arch/xtensa/mm/fault.c
@@ -112,8 +112,11 @@ good_area:
*/
fault = handle_mm_fault(vma, address, flags, regs);

- if (fault_signal_pending(fault, regs))
+ if (fault_signal_pending(fault, regs)) {
+ if (!user_mode(regs))
+ goto bad_page_fault;
return;
+ }

if (unlikely(fault & VM_FAULT_ERROR)) {
if (fault & VM_FAULT_OOM)