[Xen-changelog] [xen stable-4.9] x86: guard against #NM

[patchbot@xxxxxxx]

commit 041844ba7a0436ca877c6fa2add214124ead382a
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Jun 28 10:01:45 2018 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jun 28 10:01:45 2018 +0200

    x86: guard against #NM
    
    Just in case we still don't get CR0.TS handling right, prevent a host
    crash by honoring exception fixups in do_device_not_available(). This
    would in particular cover emulator stubs raising #NM.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: 00cebd6f22beb6d5fa65ed2d8d1ff9acf59bce61
    master date: 2018-06-28 09:08:04 +0200
---
 xen/arch/x86/traps.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 441bcd0609..3df88edb91 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -3715,7 +3715,21 @@ void do_device_not_available(struct cpu_user_regs *regs)
 {
     struct vcpu *curr = current;
 
-    BUG_ON(!guest_mode(regs));
+    if ( !guest_mode(regs) )
+    {
+        unsigned long fixup = search_exception_table(regs);
+
+        gprintk(XENLOG_ERR, "#NM: %p [%ps] -> %p\n",
+                _p(regs->rip), _p(regs->rip), _p(fixup));
+        /*
+         * We shouldn't be able to reach here, but for release builds have
+         * the recovery logic in place nevertheless.
+         */
+        ASSERT_UNREACHABLE();
+        BUG_ON(!fixup);
+        regs->rip = fixup;
+        return;
+    }
 
     vcpu_restore_fpu_lazy(curr);
 
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.9

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