x86-64: Fix CFI annotations for NMI nesting code

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.

Link: http://lkml.kernel.org/r/4F478B630200007800074A31@nat28.tlf.novell.com
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 1333d98..e0eca00 100644 (file)
--- a/arch/x86/kernel/entry_64.S
+++ b/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
 
        /*
         * If %cs was not the kernel segment, then the NMI triggered in user
@@ -1554,6 +1555,7 @@ ENTRY(nmi)
         */
        lea 6*8(%rsp), %rdx
        test_in_nmi rdx, 4*8(%rsp), nested_nmi, first_nmi
+       CFI_REMEMBER_STATE
 
 nested_nmi:
        /*
@@ -1585,10 +1587,12 @@ 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
@@ -1624,6 +1628,10 @@ 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
 
@@ -1631,14 +1639,31 @@ 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
@@ -1646,7 +1671,6 @@ 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
@@ -1675,26 +1699,6 @@ 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