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authorNicholas Piggin <npiggin@gmail.com>2022-10-14 06:07:29 +0300
committerMichael Ellerman <mpe@ellerman.id.au>2022-10-18 14:46:19 +0300
commita073672eb09670540e95a2a4aa1c46f5da74159f (patch)
tree411299c6b96893732dc0edacd16a00a19fb37d2f /arch/powerpc
parente59b3399fde5e173b026d4952b215043e77b4521 (diff)
downloadlinux-a073672eb09670540e95a2a4aa1c46f5da74159f.tar.xz
powerpc/64/interrupt: Prevent NMI PMI causing a dangerous warning
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
Diffstat (limited to 'arch/powerpc')
-rw-r--r--arch/powerpc/kernel/exceptions-64e.S7
-rw-r--r--arch/powerpc/kernel/interrupt.c12
2 files changed, 16 insertions, 3 deletions
diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
index 930e36099015..2f68fb2ee4fc 100644
--- a/arch/powerpc/kernel/exceptions-64e.S
+++ b/arch/powerpc/kernel/exceptions-64e.S
@@ -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
diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index f9db0a172401..7bc93367de68 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -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();