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Message-ID: <tip-e5862d0515ad970ccec6208ecf5bb0cffe291ea3@git.kernel.org>
Date: Thu, 19 Jul 2018 16:22:32 -0700
From: tip-bot for Joerg Roedel <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: dvlasenk@...hat.com, mingo@...nel.org, will.deacon@....com,
jgross@...e.com, tglx@...utronix.de, eduval@...zon.com,
torvalds@...ux-foundation.org, dhgutteridge@...patico.ca,
dave.hansen@...el.com, peterz@...radead.org, hpa@...or.com,
brgerst@...il.com, jpoimboe@...hat.com, luto@...nel.org,
boris.ostrovsky@...cle.com, David.Laight@...lab.com, bp@...en8.de,
aarcange@...hat.com, llong@...hat.com,
linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
jroedel@...e.de, jkosina@...e.cz, pavel@....cz
Subject: [tip:x86/pti] x86/entry/32: Leave the kernel via trampoline stack
Commit-ID: e5862d0515ad970ccec6208ecf5bb0cffe291ea3
Gitweb: https://git.kernel.org/tip/e5862d0515ad970ccec6208ecf5bb0cffe291ea3
Author: Joerg Roedel <jroedel@...e.de>
AuthorDate: Wed, 18 Jul 2018 11:40:45 +0200
Committer: Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 20 Jul 2018 01:11:37 +0200
x86/entry/32: Leave the kernel via trampoline stack
Switch back to the trampoline stack before returning to userspace.
Signed-off-by: Joerg Roedel <jroedel@...e.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Pavel Machek <pavel@....cz>
Cc: "H . Peter Anvin" <hpa@...or.com>
Cc: linux-mm@...ck.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Jiri Kosina <jkosina@...e.cz>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Brian Gerst <brgerst@...il.com>
Cc: David Laight <David.Laight@...lab.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Eduardo Valentin <eduval@...zon.com>
Cc: Greg KH <gregkh@...uxfoundation.org>
Cc: Will Deacon <will.deacon@....com>
Cc: aliguori@...zon.com
Cc: daniel.gruss@...k.tugraz.at
Cc: hughd@...gle.com
Cc: keescook@...gle.com
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Waiman Long <llong@...hat.com>
Cc: "David H . Gutteridge" <dhgutteridge@...patico.ca>
Cc: joro@...tes.org
Link: https://lkml.kernel.org/r/1531906876-13451-9-git-send-email-joro@8bytes.org
---
arch/x86/entry/entry_32.S | 79 +++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 77 insertions(+), 2 deletions(-)
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index fea49ec345ba..a905e6215ea9 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -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:
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