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xtensa: fix uaccess-related livelock in do_page_fault 

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>
This commit is contained in:
Max Filippov 2021-02-07 04:57:58 -08:00
parent ab5eb33641
commit 7b9acbb6aa
1 changed files with 4 additions and 1 deletions
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5
arch/xtensa/mm/fault.c
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@ -112,8 +112,11 @@ void do_page_fault(struct pt_regs *regs)
*/ */
fault = handle_mm_fault(vma, address, flags, regs); 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; return;
}
if (unlikely(fault & VM_FAULT_ERROR)) { if (unlikely(fault & VM_FAULT_ERROR)) {
if (fault & VM_FAULT_OOM) if (fault & VM_FAULT_OOM)