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Commit e5862d05 authored by Joerg Roedel's avatar Joerg Roedel Committed by Thomas Gleixner
Browse files

x86/entry/32: Leave the kernel via trampoline stack 



Switch back to the trampoline stack before returning to userspace.

Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Tested-by: default avatarPavel Machek <pavel@ucw.cz>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: linux-mm@kvack.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Waiman Long <llong@redhat.com>
Cc: "David H . Gutteridge" <dhgutteridge@sympatico.ca>
Cc: joro@8bytes.org
Link: https://lkml.kernel.org/r/1531906876-13451-9-git-send-email-joro@8bytes.org
parent 45d7b255

arch/x86/entry/entry_32.S

+77 −2
Original line number Diff line number Diff line
@@ -342,6 +342,60 @@ 
.Lend_\@:

.endm



/*

 * Switch back from the kernel stack to the entry stack.

 *

 * The %esp register must point to pt_regs on the task stack. It will

 * first calculate the size of the stack-frame to copy, depending on

 * whether we return to VM86 mode or not. With that it uses 'rep movsl'

 * to copy the contents of the stack over to the entry stack.

 *

 * We must be very careful here, as we can't trust the contents of the

 * task-stack once we switched to the entry-stack. When an NMI happens

 * while on the entry-stack, the NMI handler will switch back to the top

 * of the task stack, overwriting our stack-frame we are about to copy.

 * Therefore we switch the stack only after everything is copied over.

 */

.macro SWITCH_TO_ENTRY_STACK



	ALTERNATIVE     "", "jmp .Lend_\@", X86_FEATURE_XENPV



	/* Bytes to copy */

	movl	$PTREGS_SIZE, %ecx



#ifdef CONFIG_VM86

	testl	$(X86_EFLAGS_VM), PT_EFLAGS(%esp)

	jz	.Lcopy_pt_regs_\@



	/* Additional 4 registers to copy when returning to VM86 mode */

	addl    $(4 * 4), %ecx



.Lcopy_pt_regs_\@:

#endif



	/* Initialize source and destination for movsl */

	movl	PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %edi

	subl	%ecx, %edi

	movl	%esp, %esi



	/* Save future stack pointer in %ebx */

	movl	%edi, %ebx



	/* Copy over the stack-frame */

	shrl	$2, %ecx

	cld

	rep movsl



	/*

	 * Switch to entry-stack - needs to happen after everything is

	 * copied because the NMI handler will overwrite the task-stack

	 * when on entry-stack

	 */

	movl	%ebx, %esp



.Lend_\@:

.endm



/*

 * %eax: prev task

 * %edx: next task
@@ -581,25 +635,45 @@ ENTRY(entry_SYSENTER_32) 


/* Opportunistic SYSEXIT */

	TRACE_IRQS_ON			/* User mode traces as IRQs on. */



	/*

	 * Setup entry stack - we keep the pointer in %eax and do the

	 * switch after almost all user-state is restored.

	 */



	/* Load entry stack pointer and allocate frame for eflags/eax */

	movl	PER_CPU_VAR(cpu_tss_rw + TSS_sp0), %eax

	subl	$(2*4), %eax



	/* Copy eflags and eax to entry stack */

	movl	PT_EFLAGS(%esp), %edi

	movl	PT_EAX(%esp), %esi

	movl	%edi, (%eax)

	movl	%esi, 4(%eax)



	/* Restore user registers and segments */

	movl	PT_EIP(%esp), %edx	/* pt_regs->ip */

	movl	PT_OLDESP(%esp), %ecx	/* pt_regs->sp */

1:	mov	PT_FS(%esp), %fs

	PTGS_TO_GS



	popl	%ebx			/* pt_regs->bx */

	addl	$2*4, %esp		/* skip pt_regs->cx and pt_regs->dx */

	popl	%esi			/* pt_regs->si */

	popl	%edi			/* pt_regs->di */

	popl	%ebp			/* pt_regs->bp */

	popl	%eax			/* pt_regs->ax */



	/* Switch to entry stack */

	movl	%eax, %esp



	/*

	 * Restore all flags except IF. (We restore IF separately because

	 * STI gives a one-instruction window in which we won't be interrupted,

	 * whereas POPF does not.)

	 */

	addl	$PT_EFLAGS-PT_DS, %esp	/* point esp at pt_regs->flags */

	btrl	$X86_EFLAGS_IF_BIT, (%esp)

	popfl

	popl	%eax



	/*

	 * Return back to the vDSO, which will pop ecx and edx.
@@ -668,6 +742,7 @@ ENTRY(entry_INT80_32) 


restore_all:

	TRACE_IRQS_IRET

	SWITCH_TO_ENTRY_STACK

.Lrestore_all_notrace:

	CHECK_AND_APPLY_ESPFIX

.Lrestore_nocheck: