[Xen-devel] Patch "x86/entry/64/compat: Fix stack switching for XEN PV" has been added to the 4.20-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    x86/entry/64/compat: Fix stack switching for XEN PV

to the 4.20-stable tree which can be found at:
    
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-entry-64-compat-fix-stack-switching-for-xen-pv.patch
and it can be found in the queue-4.20 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


From fc24d75a7f91837d7918e40719575951820b2b8f Mon Sep 17 00:00:00 2001
From: Jan Beulich <JBeulich@xxxxxxxx>
Date: Tue, 15 Jan 2019 09:58:16 -0700
Subject: x86/entry/64/compat: Fix stack switching for XEN PV

From: Jan Beulich <JBeulich@xxxxxxxx>

commit fc24d75a7f91837d7918e40719575951820b2b8f upstream.

While in the native case entry into the kernel happens on the trampoline
stack, PV Xen kernels get entered with the current thread stack right
away. Hence source and destination stacks are identical in that case,
and special care is needed.

Other than in sync_regs() the copying done on the INT80 path isn't
NMI / #MC safe, as either of these events occurring in the middle of the
stack copying would clobber data on the (source) stack.

There is similar code in interrupt_entry() and nmi(), but there is no fixup
required because those code paths are unreachable in XEN PV guests.

[ tglx: Sanitized subject, changelog, Fixes tag and stable mail address. Sigh ]

Fixes: 7f2590a110b8 ("x86/entry/64: Use a per-CPU trampoline stack for IDT 
entries")
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Acked-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Peter Anvin <hpa@xxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: 
https://lkml.kernel.org/r/5C3E1128020000780020DFAD@xxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/x86/entry/entry_64_compat.S |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -361,7 +361,8 @@ ENTRY(entry_INT80_compat)
 
        /* Need to switch before accessing the thread stack. */
        SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
-       movq    %rsp, %rdi
+       /* In the Xen PV case we already run on the thread stack. */
+       ALTERNATIVE "movq %rsp, %rdi", "jmp .Lint80_keep_stack", 
X86_FEATURE_XENPV
        movq    PER_CPU_VAR(cpu_current_top_of_stack), %rsp
 
        pushq   6*8(%rdi)               /* regs->ss */
@@ -370,8 +371,9 @@ ENTRY(entry_INT80_compat)
        pushq   3*8(%rdi)               /* regs->cs */
        pushq   2*8(%rdi)               /* regs->ip */
        pushq   1*8(%rdi)               /* regs->orig_ax */
-
        pushq   (%rdi)                  /* pt_regs->di */
+.Lint80_keep_stack:
+
        pushq   %rsi                    /* pt_regs->si */
        xorl    %esi, %esi              /* nospec   si */
        pushq   %rdx                    /* pt_regs->dx */


Patches currently in stable-queue which might be from JBeulich@xxxxxxxx are

queue-4.20/x86-entry-64-compat-fix-stack-switching-for-xen-pv.patch

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