[PATCH] x86/emul: Assert the STI shadow when POPF sets the interrupt flag

[PATCH] x86/emul: Assert the STI shadow when POPF sets the interrupt flag

[Andrew Cooper]

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wei.liu2@citrix.com>
---
 xen/arch/x86/x86_emulate/x86_emulate.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c
index e69dfdd..e93532d 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -4061,6 +4061,12 @@ x86_emulate(
             }
         }
         dst.val &= EFLAGS_MODIFIABLE;
+
+        /* When IF transitions from 0 to 1, assert the STI shadow. */
+        if ( !(_regs.eflags & X86_EFLAGS_IF) &&
+             ((dst.val & ~mask) & X86_EFLAGS_IF) )
+            ctxt->retire.sti = true;
+
         _regs.eflags &= mask;
         _regs.eflags |= (dst.val & ~mask) | X86_EFLAGS_MBS;
         break;
-- 
2.1.4


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Re: [PATCH] x86/emul: Assert the STI shadow when POPF sets the interrupt flag

[Jan Beulich]

>>> On 06.11.18 at 15:09, <andrew.cooper3@citrix.com> wrote:
> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -4061,6 +4061,12 @@ x86_emulate(
>              }
>          }
>          dst.val &= EFLAGS_MODIFIABLE;
> +
> +        /* When IF transitions from 0 to 1, assert the STI shadow. */
> +        if ( !(_regs.eflags & X86_EFLAGS_IF) &&
> +             ((dst.val & ~mask) & X86_EFLAGS_IF) )
> +            ctxt->retire.sti = true;

I'm entirely unaware that POPF behaves the same way as STI in this
regard. Therefore: Are you sure? Can you point me to where this is
spelled out?

Jan



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