Commit 289d07a2 authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon

arm64: mm: abort uaccess retries upon fatal signal

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>
Cc: stable@vger.kernel.org
Reviewed-by: default avatarSteve Capper <steve.capper@arm.com>
Tested-by: default avatarSteve Capper <steve.capper@arm.com>
Reviewed-by: default avatarJames Morse <james.morse@arm.com>
Tested-by: default avatarJames Morse <james.morse@arm.com>
Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 09662210
......@@ -435,8 +435,11 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
* the mmap_sem because it would already be released
* in __lock_page_or_retry in mm/filemap.c.
*/
if (fatal_signal_pending(current))
if (fatal_signal_pending(current)) {
if (!user_mode(regs))
goto no_context;
return 0;
}
/*
* Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk of
......
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