The saving and restoring of %rdx wasn't annotated at all, and the
jumping over sections where state gets partly restored wasn't handled
either.
Further, by folding the pushing of the previous frame in repeat_nmi
into that which so far was immediately preceding restart_nmi (after
moving the restore of %rdx ahead of that, since it doesn't get used
anymore when pushing prior frames), annotations of the replicated
frame creations can be made consistent too.
v2: Fully fold repeat_nmi into the normal code flow (adding a single
redundant instruction to the "normal" code path), thus retaining
the special protection of all instructions between repeat_nmi and
end_repeat_nmi.
Signed-off-by: Jan Beulich <[email protected]>
Cc: Steven Rostedt <[email protected]>
---
arch/x86/kernel/entry_64.S | 52 ++++++++++++++++++++++++---------------------
1 file changed, 28 insertions(+), 24 deletions(-)
--- 3.3-rc4/arch/x86/kernel/entry_64.S
+++ 3.3-rc4-x86_64-nmi-cfi/arch/x86/kernel/entry_64.S
@@ -1530,6 +1530,7 @@ ENTRY(nmi)
/* Use %rdx as out temp variable throughout */
pushq_cfi %rdx
+ CFI_REL_OFFSET rdx, 0
/*
* Check the special variable on the stack to see if NMIs are
@@ -1547,6 +1548,7 @@ ENTRY(nmi)
*/
lea 6*8(%rsp), %rdx
test_in_nmi rdx, 4*8(%rsp), nested_nmi, first_nmi
+ CFI_REMEMBER_STATE
nested_nmi:
/*
@@ -1578,10 +1580,12 @@ nested_nmi:
nested_nmi_out:
popq_cfi %rdx
+ CFI_RESTORE rdx
/* No need to check faults here */
INTERRUPT_RETURN
+ CFI_RESTORE_STATE
first_nmi:
/*
* Because nested NMIs will use the pushed location that we
@@ -1617,6 +1621,10 @@ first_nmi:
* NMI may zero out. The original stack frame and the temp storage
* is also used by nested NMIs and can not be trusted on exit.
*/
+ /* Do not pop rdx, nested NMIs will corrupt it */
+ movq (%rsp), %rdx
+ CFI_RESTORE rdx
+
/* Set the NMI executing variable on the stack. */
pushq_cfi $1
@@ -1624,14 +1632,31 @@ first_nmi:
.rept 5
pushq_cfi 6*8(%rsp)
.endr
+ CFI_DEF_CFA_OFFSET SS+8-RIP
+
+ /*
+ * If there was a nested NMI, the first NMI's iret will return
+ * here. But NMIs are still enabled and we can take another
+ * nested NMI. The nested NMI checks the interrupted RIP to see
+ * if it is between repeat_nmi and end_repeat_nmi, and if so
+ * it will just return, as we are about to repeat an NMI anyway.
+ * This makes it safe to copy to the stack frame that a nested
+ * NMI will update.
+ */
+repeat_nmi:
+ /*
+ * Update the stack variable to say we are still in NMI (the update
+ * is benign for the non-repeat case, where 1 was pushed just above
+ * to this very stack slot).
+ */
+ movq $1, 5*8(%rsp)
/* Make another copy, this one may be modified by nested NMIs */
.rept 5
pushq_cfi 4*8(%rsp)
.endr
-
- /* Do not pop rdx, nested NMIs will corrupt it */
- movq 11*8(%rsp), %rdx
+ CFI_DEF_CFA_OFFSET SS+8-RIP
+end_repeat_nmi:
/*
* Everything below this point can be preempted by a nested
@@ -1639,7 +1664,6 @@ first_nmi:
* caused by an exception and nested NMI will start here, and
* can still be preempted by another NMI.
*/
-restart_nmi:
pushq_cfi $-1 /* ORIG_RAX: no syscall to restart */
subq $ORIG_RAX-R15, %rsp
CFI_ADJUST_CFA_OFFSET ORIG_RAX-R15
@@ -1668,26 +1692,6 @@ nmi_restore:
CFI_ENDPROC
END(nmi)
- /*
- * If an NMI hit an iret because of an exception or breakpoint,
- * it can lose its NMI context, and a nested NMI may come in.
- * In that case, the nested NMI will change the preempted NMI's
- * stack to jump to here when it does the final iret.
- */
-repeat_nmi:
- INTR_FRAME
- /* Update the stack variable to say we are still in NMI */
- movq $1, 5*8(%rsp)
-
- /* copy the saved stack back to copy stack */
- .rept 5
- pushq_cfi 4*8(%rsp)
- .endr
-
- jmp restart_nmi
- CFI_ENDPROC
-end_repeat_nmi:
-
ENTRY(ignore_sysret)
CFI_STARTPROC
mov $-ENOSYS,%eax
On Fri, 2012-02-24 at 14:54 +0000, Jan Beulich wrote:
> The saving and restoring of %rdx wasn't annotated at all, and the
> jumping over sections where state gets partly restored wasn't handled
> either.
>
> Further, by folding the pushing of the previous frame in repeat_nmi
> into that which so far was immediately preceding restart_nmi (after
> moving the restore of %rdx ahead of that, since it doesn't get used
> anymore when pushing prior frames), annotations of the replicated
> frame creations can be made consistent too.
>
> v2: Fully fold repeat_nmi into the normal code flow (adding a single
> redundant instruction to the "normal" code path), thus retaining
> the special protection of all instructions between repeat_nmi and
> end_repeat_nmi.
Thanks, I'll start testing it.
>
> Signed-off-by: Jan Beulich <[email protected]>
> Cc: Steven Rostedt <[email protected]>
FYI, please send to my [email protected] account. My RH account is a
second class citizen that I use to read RH status updates and such. I
don't conduct upstream work from it and I may ignore it for long periods
of time.
I author code with it just to give credit to the company that pays me,
but my SOB is always the goodmis.org account.
Thanks,
-- Steve