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Commit 929bacec authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
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x86/entry/64: De-Xen-ify our NMI code 



Xen PV is fundamentally incompatible with our fancy NMI code: it
doesn't use IST at all, and Xen entries clobber two stack slots
below the hardware frame.

Drop Xen PV support from our NMI code entirely.

Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Reviewed-by: default avatarBorislav Petkov <bp@suse.de>
Acked-by: default avatarJuergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/bfbe711b5ae03f672f8848999a8eb2711efc7f98.1509609304.git.luto@kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 43e41110

arch/x86/entry/entry_64.S

+18 −12
Original line number Original line Diff line number Diff line
@@ -1240,9 +1240,13 @@ ENTRY(error_exit) 
	jmp	retint_user

	jmp	retint_user

END(error_exit)

END(error_exit)





/* Runs on exception stack */

/*

 * Runs on exception stack.  Xen PV does not go through this path at all,

 * so we can use real assembly here.

 */

ENTRY(nmi)

ENTRY(nmi)

	UNWIND_HINT_IRET_REGS

	UNWIND_HINT_IRET_REGS



	/*

	/*

	 * We allow breakpoints in NMIs. If a breakpoint occurs, then

	 * We allow breakpoints in NMIs. If a breakpoint occurs, then

	 * the iretq it performs will take us out of NMI context.

	 * the iretq it performs will take us out of NMI context.
@@ -1300,7 +1304,7 @@ ENTRY(nmi) 
	 * stacks lest we corrupt the "NMI executing" variable.

	 * stacks lest we corrupt the "NMI executing" variable.

	 */

	 */





	SWAPGS_UNSAFE_STACK

	swapgs

	cld

	cld

	movq	%rsp, %rdx

	movq	%rsp, %rdx

	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp

	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp
@@ -1465,7 +1469,7 @@ nested_nmi_out: 
	popq	%rdx

	popq	%rdx





	/* We are returning to kernel mode, so this cannot result in a fault. */

	/* We are returning to kernel mode, so this cannot result in a fault. */

	INTERRUPT_RETURN

	iretq





first_nmi:

first_nmi:

	/* Restore rdx. */

	/* Restore rdx. */
@@ -1496,7 +1500,7 @@ first_nmi: 
	pushfq			/* RFLAGS */

	pushfq			/* RFLAGS */

	pushq	$__KERNEL_CS	/* CS */

	pushq	$__KERNEL_CS	/* CS */

	pushq	$1f		/* RIP */

	pushq	$1f		/* RIP */

	INTERRUPT_RETURN	/* continues at repeat_nmi below */

	iretq			/* continues at repeat_nmi below */

	UNWIND_HINT_IRET_REGS

	UNWIND_HINT_IRET_REGS

1:

1:

#endif

#endif
@@ -1571,20 +1575,22 @@ nmi_restore: 
	/*

	/*

	 * Clear "NMI executing".  Set DF first so that we can easily

	 * Clear "NMI executing".  Set DF first so that we can easily

	 * distinguish the remaining code between here and IRET from

	 * distinguish the remaining code between here and IRET from

	 * the SYSCALL entry and exit paths.  On a native kernel, we

	 * the SYSCALL entry and exit paths.

	 * could just inspect RIP, but, on paravirt kernels,

	 *

	 * INTERRUPT_RETURN can translate into a jump into a

	 * We arguably should just inspect RIP instead, but I (Andy) wrote

	 * hypercall page.

	 * this code when I had the misapprehension that Xen PV supported

	 * NMIs, and Xen PV would break that approach.

	 */

	 */

	std

	std

	movq	$0, 5*8(%rsp)		/* clear "NMI executing" */

	movq	$0, 5*8(%rsp)		/* clear "NMI executing" */





	/*

	/*

	 * INTERRUPT_RETURN reads the "iret" frame and exits the NMI

	 * iretq reads the "iret" frame and exits the NMI stack in a

	 * stack in a single instruction.  We are returning to kernel

	 * single instruction.  We are returning to kernel mode, so this

	 * mode, so this cannot result in a fault.

	 * cannot result in a fault.  Similarly, we don't need to worry

	 * about espfix64 on the way back to kernel mode.

	 */

	 */

	INTERRUPT_RETURN

	iretq

END(nmi)

END(nmi)





ENTRY(ignore_sysret)

ENTRY(ignore_sysret)