Re: [Xen-devel] [PATCH] x86_emulate: split the {reg, mem} union in struct operand.

[Tim Deegan <tim@xxxxxxx>]

At 12:25 +0000 on 26 Mar (1427372755), Andrew Cooper wrote:
> On 26/03/15 12:16, Tim Deegan wrote:
> > In the hopes of making any future errors along the lines of XSA-123
> > into clean crashes instead of memory corruption bugs.
> >
> > Signed-off-by: Tim Deegan <tim@xxxxxxx>
> > CC: Keir Fraser <keir@xxxxxxx>
> > CC: Jan Beulich <jbeulich@xxxxxxxx>
> > CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> 
> I am very much in favour of this change.
> 
> Does REG_POISON work with a 32bit compile of the test harness?

No it will not.  v2 on its way...

> Independent of this, it might be easier to spot in crashes if the upper 
> word of the address was also 8086

Sure, why not?

Tim.

> > ---
> >   xen/arch/x86/x86_emulate/x86_emulate.c | 8 +++++---
> >   1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c 
> > b/xen/arch/x86/x86_emulate/x86_emulate.c
> > index c082c9e..37d1fea 100644
> > --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> > +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> > @@ -319,7 +319,7 @@ struct operand {
> >       /* Original operand value. */
> >       unsigned long orig_val;
> >   
> > -    union {
> > +    struct {
> >           /* OP_REG: Pointer to register field. */
> >           unsigned long *reg;
> >           /* OP_MEM: Segment and offset. */
> > @@ -329,6 +329,7 @@ struct operand {
> >           } mem;
> >       };
> >   };
> > +#define REG_POISON ((unsigned long *) 0x8000000000008086UL) /* 
> > non-canonical */
> >   
> >   typedef union {
> >       uint64_t mmx;
> > @@ -1447,14 +1448,15 @@ x86_emulate(
> >       unsigned int op_bytes, def_op_bytes, ad_bytes, def_ad_bytes;
> >       bool_t lock_prefix = 0;
> >       int override_seg = -1, rc = X86EMUL_OKAY;
> > -    struct operand src, dst;
> > +    struct operand src = { .reg = REG_POISON };
> > +    struct operand dst = { .reg = REG_POISON };
> >       enum x86_swint_type swint_type;
> >       DECLARE_ALIGNED(mmval_t, mmval);
> >       /*
> >        * Data operand effective address (usually computed from ModRM).
> >        * Default is a memory operand relative to segment DS.
> >        */
> > -    struct operand ea = { .type = OP_MEM };
> > +    struct operand ea = { .type = OP_MEM, .reg = REG_POISON };
> >       ea.mem.seg = x86_seg_ds; /* gcc may reject anon union initializer */
> >   
> >       ctxt->retire.byte = 0;
> 

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel