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Commit 1d3e53e8 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar
Browse files

x86/entry/64: Refactor IRQ stacks and make them NMI-safe 



This will allow IRQ stacks to nest inside NMIs or similar entries
that can happen during IRQ stack setup or teardown.

The new macros won't work correctly if they're invoked with IRQs on.
Add a check under CONFIG_DEBUG_ENTRY to detect that.

Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
[ Use %r10 instead of %r11 in xen_do_hypervisor_callback to make objtool
  and ORC unwinder's lives a little easier. ]
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/b0b2ff5fb97d2da2e1d7e1f380190c92545c8bb5.1499786555.git.jpoimboe@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent cb8c65cc

arch/x86/Kconfig.debug

+0 −2
Original line number Diff line number Diff line
@@ -305,8 +305,6 @@ config DEBUG_ENTRY 
	  Some of these sanity checks may slow down kernel entries and

	  exits or otherwise impact performance.



	  This is currently used to help test NMI code.



	  If unsure, say N.



config DEBUG_NMI_SELFTEST

arch/x86/entry/entry_64.S

+61 −24
Original line number Diff line number Diff line
@@ -447,6 +447,59 @@ ENTRY(irq_entries_start) 
    .endr

END(irq_entries_start)



.macro DEBUG_ENTRY_ASSERT_IRQS_OFF

#ifdef CONFIG_DEBUG_ENTRY

	pushfq

	testl $X86_EFLAGS_IF, (%rsp)

	jz .Lokay_\@

	ud2

.Lokay_\@:

	addq $8, %rsp

#endif

.endm



/*

 * Enters the IRQ stack if we're not already using it.  NMI-safe.  Clobbers

 * flags and puts old RSP into old_rsp, and leaves all other GPRs alone.

 * Requires kernel GSBASE.

 *

 * The invariant is that, if irq_count != -1, then the IRQ stack is in use.

 */

.macro ENTER_IRQ_STACK old_rsp

	DEBUG_ENTRY_ASSERT_IRQS_OFF

	movq	%rsp, \old_rsp

	incl	PER_CPU_VAR(irq_count)



	/*

	 * Right now, if we just incremented irq_count to zero, we've

	 * claimed the IRQ stack but we haven't switched to it yet.

	 *

	 * If anything is added that can interrupt us here without using IST,

	 * it must be *extremely* careful to limit its stack usage.  This

	 * could include kprobes and a hypothetical future IST-less #DB

	 * handler.

	 */



	cmovzq	PER_CPU_VAR(irq_stack_ptr), %rsp

	pushq	\old_rsp

.endm



/*

 * Undoes ENTER_IRQ_STACK.

 */

.macro LEAVE_IRQ_STACK

	DEBUG_ENTRY_ASSERT_IRQS_OFF

	/* We need to be off the IRQ stack before decrementing irq_count. */

	popq	%rsp



	/*

	 * As in ENTER_IRQ_STACK, irq_count == 0, we are still claiming

	 * the irq stack but we're not on it.

	 */



	decl	PER_CPU_VAR(irq_count)

.endm



/*

 * Interrupt entry/exit.

 *
@@ -485,17 +538,7 @@ END(irq_entries_start) 
	CALL_enter_from_user_mode



1:

	/*

	 * Save previous stack pointer, optionally switch to interrupt stack.

	 * irq_count is used to check if a CPU is already on an interrupt stack

	 * or not. While this is essentially redundant with preempt_count it is

	 * a little cheaper to use a separate counter in the PDA (short of

	 * moving irq_enter into assembly, which would be too much work)

	 */

	movq	%rsp, %rdi

	incl	PER_CPU_VAR(irq_count)

	cmovzq	PER_CPU_VAR(irq_stack_ptr), %rsp

	pushq	%rdi

	ENTER_IRQ_STACK old_rsp=%rdi

	/* We entered an interrupt context - irqs are off: */

	TRACE_IRQS_OFF
@@ -515,10 +558,8 @@ common_interrupt: 
ret_from_intr:

	DISABLE_INTERRUPTS(CLBR_ANY)

	TRACE_IRQS_OFF

	decl	PER_CPU_VAR(irq_count)



	/* Restore saved previous stack */

	popq	%rsp

	LEAVE_IRQ_STACK



	testb	$3, CS(%rsp)

	jz	retint_kernel
@@ -891,12 +932,10 @@ bad_gs: 
ENTRY(do_softirq_own_stack)

	pushq	%rbp

	mov	%rsp, %rbp

	incl	PER_CPU_VAR(irq_count)

	cmove	PER_CPU_VAR(irq_stack_ptr), %rsp

	push	%rbp				/* frame pointer backlink */

	ENTER_IRQ_STACK old_rsp=%r11

	call	__do_softirq

	LEAVE_IRQ_STACK

	leaveq

	decl	PER_CPU_VAR(irq_count)

	ret

END(do_softirq_own_stack)
@@ -923,13 +962,11 @@ ENTRY(xen_do_hypervisor_callback) /* do_hypervisor_callback(struct *pt_regs) */ 
 * see the correct pointer to the pt_regs

 */

	movq	%rdi, %rsp			/* we don't return, adjust the stack frame */

11:	incl	PER_CPU_VAR(irq_count)

	movq	%rsp, %rbp

	cmovzq	PER_CPU_VAR(irq_stack_ptr), %rsp

	pushq	%rbp				/* frame pointer backlink */



	ENTER_IRQ_STACK old_rsp=%r10

	call	xen_evtchn_do_upcall

	popq	%rsp

	decl	PER_CPU_VAR(irq_count)

	LEAVE_IRQ_STACK



#ifndef CONFIG_PREEMPT

	call	xen_maybe_preempt_hcall

#endif

arch/x86/kernel/process_64.c

+3 −0
Original line number Diff line number Diff line
@@ -279,6 +279,9 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) 
	struct tss_struct *tss = &per_cpu(cpu_tss, cpu);

	unsigned prev_fsindex, prev_gsindex;



	WARN_ON_ONCE(IS_ENABLED(CONFIG_DEBUG_ENTRY) &&

		     this_cpu_read(irq_count) != -1);



	switch_fpu_prepare(prev_fpu, cpu);



	/* We must save %fs and %gs before load_TLS() because