92 lines
3.2 KiB
Diff
92 lines
3.2 KiB
Diff
From: Andy Lutomirski <luto@kernel.org>
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Date: Wed, 15 Jul 2015 10:29:37 -0700
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Subject: [8/9] x86/nmi/64: Reorder nested NMI checks
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Origin: https://git.kernel.org/linus/a27507ca2d796cfa8d907de31ad730359c8a6d06
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Check the repeat_nmi .. end_repeat_nmi special case first. The
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next patch will rework the RSP check and, as a side effect, the
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RSP check will no longer detect repeat_nmi .. end_repeat_nmi, so
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we'll need this ordering of the checks.
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Note: this is more subtle than it appears. The check for
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repeat_nmi .. end_repeat_nmi jumps straight out of the NMI code
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instead of adjusting the "iret" frame to force a repeat. This
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is necessary, because the code between repeat_nmi and
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end_repeat_nmi sets "NMI executing" and then writes to the
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"iret" frame itself. If a nested NMI comes in and modifies the
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"iret" frame while repeat_nmi is also modifying it, we'll end up
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with garbage. The old code got this right, as does the new
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code, but the new code is a bit more explicit.
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If we were to move the check right after the "NMI executing"
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check, then we'd get it wrong and have random crashes.
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( Because the "NMI executing" check would jump to the code that would
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modify the "iret" frame without checking if the interrupted NMI was
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currently modifying it. )
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Signed-off-by: Andy Lutomirski <luto@kernel.org>
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Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
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Cc: Borislav Petkov <bp@suse.de>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>
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Cc: Peter Zijlstra <peterz@infradead.org>
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Cc: Thomas Gleixner <tglx@linutronix.de>
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Cc: stable@vger.kernel.org
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Signed-off-by: Ingo Molnar <mingo@kernel.org>
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[bwh: Backported to 4.0: adjust filename, spacing]
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Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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---
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arch/x86/kernel/entry_64.S | 34 ++++++++++++++++++----------------
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1 file changed, 18 insertions(+), 16 deletions(-)
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--- a/arch/x86/kernel/entry_64.S
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+++ b/arch/x86/kernel/entry_64.S
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@@ -1623,7 +1623,24 @@ ENTRY(nmi)
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/*
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* Determine whether we're a nested NMI.
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*
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- * First check "NMI executing". If it's set, then we're nested.
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+ * If we interrupted kernel code between repeat_nmi and
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+ * end_repeat_nmi, then we are a nested NMI. We must not
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+ * modify the "iret" frame because it's being written by
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+ * the outer NMI. That's okay; the outer NMI handler is
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+ * about to about to call do_nmi anyway, so we can just
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+ * resume the outer NMI.
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+ */
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+
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+ movq $repeat_nmi, %rdx
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+ cmpq 8(%rsp), %rdx
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+ ja 1f
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+ movq $end_repeat_nmi, %rdx
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+ cmpq 8(%rsp), %rdx
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+ ja nested_nmi_out
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+1:
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+
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+ /*
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+ * Now check "NMI executing". If it's set, then we're nested.
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* This will not detect if we interrupted an outer NMI just
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* before IRET.
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*/
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@@ -1650,21 +1667,6 @@ ENTRY(nmi)
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nested_nmi:
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/*
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- * If we interrupted an NMI that is between repeat_nmi and
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- * end_repeat_nmi, then we must not modify the "iret" frame
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- * because it's being written by the outer NMI. That's okay;
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- * the outer NMI handler is about to call do_nmi anyway,
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- * so we can just resume the outer NMI.
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- */
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- movq $repeat_nmi, %rdx
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- cmpq 8(%rsp), %rdx
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- ja 1f
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- movq $end_repeat_nmi, %rdx
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- cmpq 8(%rsp), %rdx
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- ja nested_nmi_out
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-
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-1:
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- /*
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* Modify the "iret" frame to point to repeat_nmi, forcing another
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* iteration of NMI handling.
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*/
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