From fceb90bb43ca5c01eff73367f71a76c06f049b41 Mon Sep 17 00:00:00 2001 From: Thomas Bogendoerfer Date: Thu, 21 Jan 2021 17:04:16 +0100 Subject: [PATCH] MIPS: mm: abort uaccess retries upon fatal signal When there's a fatal signal pending, MIPS's do_page_fault() implementation returns. 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. [ Description taken from commit 746a272e4414 ("ARM: 8692/1: mm: abort uaccess retries upon fatal signal") ] Signed-off-by: Thomas Bogendoerfer Acked-by: Mark Rutland --- arch/mips/mm/fault.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/mips/mm/fault.c b/arch/mips/mm/fault.c index 7c871b14e74a..e7abda9c013f 100644 --- a/arch/mips/mm/fault.c +++ b/arch/mips/mm/fault.c @@ -156,8 +156,11 @@ 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 no_context; return; + } if (unlikely(fault & VM_FAULT_ERROR)) { if (fault & VM_FAULT_OOM) -- 2.20.1