Commit 62610913 authored by Jan Beulich's avatar Jan Beulich Committed by Steven Rostedt
Browse files

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: default avatarJan Beulich <jbeulich@suse.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent a38449ef

arch/x86/kernel/entry_64.S

+28 −24
Original line number Diff line number Diff line
@@ -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

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