Re: [Xen-devel] [PATCH] x86/pv: Check that emulate_privileged_op() don't change any unexpected flags

[Jan Beulich]

>>> On 16.01.17 at 14:03,  wrote:
> No bits, other than arithmetic ones and the resume flag (which will most
> likely change from 1 to 0), can be changed by the instructions we permit.
> Extend the check to cover other flags.
> 
> Signed-off-by: Andrew Cooper 

Reviewed-by: Jan Beulich 



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[Xen-devel] [PATCH] x86/pv: Check that emulate_privileged_op() don't change any unexpected flags

[Andrew Cooper]

No bits, other than arithmetic ones and the resume flag (which will most
likely change from 1 to 0), can be changed by the instructions we permit.
Extend the check to cover other flags.

Signed-off-by: Andrew Cooper 
---
CC: Jan Beulich 

v2:
 * Extend to all unexpected bits.
---
 xen/arch/x86/traps.c | 6 --
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 4f29c3a..ea0ce52 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -3012,9 +3012,11 @@ static int emulate_privileged_op(struct cpu_user_regs 
*regs)
 
 /*
  * Un-mirror virtualized state from EFLAGS.
- * Nothing we allow to be emulated can change TF, IF, or IOPL.
+ * Nothing we allow to be emulated can change anything other than the
+ * arithmetic bits, and the resume flag.
  */
-ASSERT(!((regs->_eflags ^ eflags) & (X86_EFLAGS_IF | X86_EFLAGS_IOPL)));
+ASSERT(!((regs->_eflags ^ eflags) &
+ ~(X86_EFLAGS_RF | X86_EFLAGS_ARITH_MASK)));
 regs->_eflags |= X86_EFLAGS_IF;
 regs->_eflags &= ~X86_EFLAGS_IOPL;
 
-- 
2.1.4


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