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powerpc/64/interrupt: Prevent NMI PMI causing a dangerous warning

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NMI PMIs really should not return using the normal interrupt_return
function. If such a PMI hits in code returning to user with the context
switched to user mode, this warning can fire. This was enough to cause
crashes when reproducing on 64s, because another perf interrupt would
hit while reporting bug, and that would cause another bug, and so on
until smashing the stack.

Work around that particular crash for now by just disabling that context
warning for PMIs. This is a hack and not a complete fix, there could be
other such problems lurking in corners. But it does fix the known crash.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221014030729.2077151-3-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin 2022-10-14 13:07:29 +10:00 committed by Michael Ellerman
parent e59b3399fd
commit a073672eb0
2 changed files with 16 additions and 3 deletions
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7
arch/powerpc/kernel/exceptions-64e.S
View File

@ -813,6 +813,13 @@ kernel_dbg_exc:
EXCEPTION_COMMON(0x260)
CHECK_NAPPING()
addi r3,r1,STACK_FRAME_OVERHEAD
/*
* XXX: Returning from performance_monitor_exception taken as a
* soft-NMI (Linux irqs disabled) may be risky to use interrupt_return
* and could cause bugs in return or elsewhere. That case should just
* restore registers and return. There is a workaround for one known
* problem in interrupt_exit_kernel_prepare().
*/
bl performance_monitor_exception
b interrupt_return

12
arch/powerpc/kernel/interrupt.c
View File

@ -374,10 +374,16 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
if (regs_is_unrecoverable(regs))
unrecoverable_exception(regs);
/*
* CT_WARN_ON comes here via program_check_exception,
* so avoid recursion.
* CT_WARN_ON comes here via program_check_exception, so avoid
* recursion.
*
* Skip the assertion on PMIs to work around a problem caused by NMI
* PMIs incorrectly taking this interrupt return path, it's possible
* for this to hit after interrupt exit to user switches context to
* user. See also the comment in the performance monitor handler in
* exceptions-64e/s.S
*/
if (TRAP(regs) != INTERRUPT_PROGRAM)
if (TRAP(regs) != INTERRUPT_PROGRAM && TRAP(regs) != INTERRUPT_PERFMON)
CT_WARN_ON(ct_state() == CONTEXT_USER);
kuap = kuap_get_and_assert_locked();