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x86: don't leak ST(n)/XMMn values to domains first using them
FNINIT doesn't alter these registers, and hence using it is
insufficient to initialize a guest's initial state.
This is XSA-165.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -851,6 +851,17 @@ int arch_set_info_guest(
if ( v->arch.xsave_area )
v->arch.xsave_area->xsave_hdr.xstate_bv = XSTATE_FP_SSE;
}
+ else if ( v->arch.xsave_area )
+ memset(&v->arch.xsave_area->xsave_hdr, 0,
+ sizeof(v->arch.xsave_area->xsave_hdr));
+ else
+ {
+ typeof(v->arch.xsave_area->fpu_sse) *fpu_sse = v->arch.fpu_ctxt;
+
+ memset(fpu_sse, 0, sizeof(*fpu_sse));
+ fpu_sse->fcw = FCW_DEFAULT;
+ fpu_sse->mxcsr = MXCSR_DEFAULT;
+ }
if ( !compat )
{
--- a/xen/arch/x86/i387.c
+++ b/xen/arch/x86/i387.c
@@ -17,19 +17,6 @@
#include <asm/xstate.h>
#include <asm/asm_defns.h>
-static void fpu_init(void)
-{
- unsigned long val;
-
- asm volatile ( "fninit" );
- if ( cpu_has_xmm )
- {
- /* load default value into MXCSR control/status register */
- val = MXCSR_DEFAULT;
- asm volatile ( "ldmxcsr %0" : : "m" (val) );
- }
-}
-
/*******************************/
/* FPU Restore Functions */
/*******************************/
@@ -248,15 +235,8 @@ void vcpu_restore_fpu_lazy(struct vcpu *
if ( cpu_has_xsave )
fpu_xrstor(v, XSTATE_LAZY);
- else if ( v->fpu_initialised )
- {
- if ( cpu_has_fxsr )
- fpu_fxrstor(v);
- else
- fpu_frstor(v);
- }
else
- fpu_init();
+ fpu_fxrstor(v);
v->fpu_initialised = 1;
v->fpu_dirtied = 1;
@@ -313,7 +293,14 @@ int vcpu_init_fpu(struct vcpu *v)
else
{
v->arch.fpu_ctxt = _xzalloc(sizeof(v->arch.xsave_area->fpu_sse), 16);
- if ( !v->arch.fpu_ctxt )
+ if ( v->arch.fpu_ctxt )
+ {
+ typeof(v->arch.xsave_area->fpu_sse) *fpu_sse = v->arch.fpu_ctxt;
+
+ fpu_sse->fcw = FCW_DEFAULT;
+ fpu_sse->mxcsr = MXCSR_DEFAULT;
+ }
+ else
rc = -ENOMEM;
}
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