From mboxrd@z Thu Jan 1 00:00:00 1970 From: mark.rutland@arm.com (Mark Rutland) Date: Tue, 11 Jul 2017 15:19:22 +0100 Subject: [PATCH 1/2] arm64: mm: abort uaccess retries upon fatal signal In-Reply-To: <1499782763-31418-1-git-send-email-mark.rutland@arm.com> References: <1499782763-31418-1-git-send-email-mark.rutland@arm.com> Message-ID: <1499782763-31418-2-git-send-email-mark.rutland@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. Signed-off-by: Mark Rutland Reviewed-by: Steve Capper Tested-by: Steve Capper Cc: Catalin Marinas Cc: James Morse Cc: Laura Abbott Cc: Will Deacon Cc: stable at vger.kernel.org --- arch/arm64/mm/fault.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 37b95df..3952d5e 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -397,8 +397,11 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, * 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 -- 1.9.1