* [PATCH] x86emul: special case far branch validation outside of long mode
@ 2016-03-11 16:01 Jan Beulich
2016-04-21 8:36 ` Andrew Cooper
0 siblings, 1 reply; 4+ messages in thread
From: Jan Beulich @ 2016-03-11 16:01 UTC (permalink / raw)
To: xen-devel; +Cc: Andrew Cooper, Keir Fraser
[-- Attachment #1: Type: text/plain, Size: 3475 bytes --]
In that case (with the new value being held in, or now in one case cast
to, a 32-bit variable) there's no need to go through the long mode part
of the checks.
Primarily this was meant to hopefully address Coverity ID 1355278, but
since the change produces smaller code as well I think we should use it
even if it doesn't help that (benign) warning.
Also it's more in line with jmp_rel() for commit_far_branch() to do the
_regs.eip update, so adjust that at once.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -652,13 +652,20 @@ do {
_regs.eip = ip; \
} while (0)
-#define validate_far_branch(cs, ip) \
- generate_exception_if(in_longmode(ctxt, ops) && (cs)->attr.fields.l \
- ? !is_canonical_address(ip) \
- : (ip) > (cs)->limit, EXC_GP, 0)
+#define validate_far_branch(cs, ip) ({ \
+ if ( sizeof(ip) <= 4 ) { \
+ ASSERT(in_longmode(ctxt, ops) <= 0); \
+ generate_exception_if((ip) > (cs)->limit, EXC_GP, 0); \
+ } else \
+ generate_exception_if(in_longmode(ctxt, ops) && \
+ (cs)->attr.fields.l \
+ ? !is_canonical_address(ip) \
+ : (ip) > (cs)->limit, EXC_GP, 0); \
+})
#define commit_far_branch(cs, ip) ({ \
validate_far_branch(cs, ip); \
+ _regs.eip = (ip); \
ops->write_segment(x86_seg_cs, cs, ctxt); \
})
@@ -2787,7 +2794,6 @@ x86_emulate(
(rc = load_seg(x86_seg_cs, src.val, 1, &cs, ctxt, ops)) ||
(rc = commit_far_branch(&cs, dst.val)) )
goto done;
- _regs.eip = dst.val;
break;
}
@@ -2830,9 +2836,8 @@ x86_emulate(
eflags &= 0x257fd5;
_regs.eflags &= mask;
_regs.eflags |= (eflags & ~mask) | 0x02;
- _regs.eip = eip;
if ( (rc = load_seg(x86_seg_cs, sel, 1, &cs, ctxt, ops)) ||
- (rc = commit_far_branch(&cs, eip)) )
+ (rc = commit_far_branch(&cs, (uint32_t)eip)) )
goto done;
break;
}
@@ -3465,7 +3470,6 @@ x86_emulate(
if ( (rc = load_seg(x86_seg_cs, sel, 0, &cs, ctxt, ops)) ||
(rc = commit_far_branch(&cs, eip)) )
goto done;
- _regs.eip = eip;
break;
}
@@ -3767,11 +3771,11 @@ x86_emulate(
&_regs.eip, op_bytes, ctxt)) ||
(rc = ops->write_segment(x86_seg_cs, &cs, ctxt)) )
goto done;
+ _regs.eip = src.val;
}
else if ( (rc = load_seg(x86_seg_cs, sel, 0, &cs, ctxt, ops)) ||
(rc = commit_far_branch(&cs, src.val)) )
goto done;
- _regs.eip = src.val;
dst.type = OP_NONE;
break;
[-- Attachment #2: x86emul-coverity-warning.patch --]
[-- Type: text/plain, Size: 3537 bytes --]
x86emul: special case far branch validation outside of long mode
In that case (with the new value being held in, or now in one case cast
to, a 32-bit variable) there's no need to go through the long mode part
of the checks.
Primarily this was meant to hopefully address Coverity ID 1355278, but
since the change produces smaller code as well I think we should use it
even if it doesn't help that (benign) warning.
Also it's more in line with jmp_rel() for commit_far_branch() to do the
_regs.eip update, so adjust that at once.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -652,13 +652,20 @@ do {
_regs.eip = ip; \
} while (0)
-#define validate_far_branch(cs, ip) \
- generate_exception_if(in_longmode(ctxt, ops) && (cs)->attr.fields.l \
- ? !is_canonical_address(ip) \
- : (ip) > (cs)->limit, EXC_GP, 0)
+#define validate_far_branch(cs, ip) ({ \
+ if ( sizeof(ip) <= 4 ) { \
+ ASSERT(in_longmode(ctxt, ops) <= 0); \
+ generate_exception_if((ip) > (cs)->limit, EXC_GP, 0); \
+ } else \
+ generate_exception_if(in_longmode(ctxt, ops) && \
+ (cs)->attr.fields.l \
+ ? !is_canonical_address(ip) \
+ : (ip) > (cs)->limit, EXC_GP, 0); \
+})
#define commit_far_branch(cs, ip) ({ \
validate_far_branch(cs, ip); \
+ _regs.eip = (ip); \
ops->write_segment(x86_seg_cs, cs, ctxt); \
})
@@ -2787,7 +2794,6 @@ x86_emulate(
(rc = load_seg(x86_seg_cs, src.val, 1, &cs, ctxt, ops)) ||
(rc = commit_far_branch(&cs, dst.val)) )
goto done;
- _regs.eip = dst.val;
break;
}
@@ -2830,9 +2836,8 @@ x86_emulate(
eflags &= 0x257fd5;
_regs.eflags &= mask;
_regs.eflags |= (eflags & ~mask) | 0x02;
- _regs.eip = eip;
if ( (rc = load_seg(x86_seg_cs, sel, 1, &cs, ctxt, ops)) ||
- (rc = commit_far_branch(&cs, eip)) )
+ (rc = commit_far_branch(&cs, (uint32_t)eip)) )
goto done;
break;
}
@@ -3465,7 +3470,6 @@ x86_emulate(
if ( (rc = load_seg(x86_seg_cs, sel, 0, &cs, ctxt, ops)) ||
(rc = commit_far_branch(&cs, eip)) )
goto done;
- _regs.eip = eip;
break;
}
@@ -3767,11 +3771,11 @@ x86_emulate(
&_regs.eip, op_bytes, ctxt)) ||
(rc = ops->write_segment(x86_seg_cs, &cs, ctxt)) )
goto done;
+ _regs.eip = src.val;
}
else if ( (rc = load_seg(x86_seg_cs, sel, 0, &cs, ctxt, ops)) ||
(rc = commit_far_branch(&cs, src.val)) )
goto done;
- _regs.eip = src.val;
dst.type = OP_NONE;
break;
[-- Attachment #3: Type: text/plain, Size: 126 bytes --]
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^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] x86emul: special case far branch validation outside of long mode
2016-03-11 16:01 [PATCH] x86emul: special case far branch validation outside of long mode Jan Beulich
@ 2016-04-21 8:36 ` Andrew Cooper
2016-04-21 8:55 ` Jan Beulich
0 siblings, 1 reply; 4+ messages in thread
From: Andrew Cooper @ 2016-04-21 8:36 UTC (permalink / raw)
To: Jan Beulich, xen-devel; +Cc: Keir Fraser
On 11/03/16 16:01, Jan Beulich wrote:
> In that case (with the new value being held in, or now in one case cast
> to, a 32-bit variable) there's no need to go through the long mode part
> of the checks.
>
> Primarily this was meant to hopefully address Coverity ID 1355278, but
> since the change produces smaller code as well I think we should use it
> even if it doesn't help that (benign) warning.
>
> Also it's more in line with jmp_rel() for commit_far_branch() to do the
> _regs.eip update, so adjust that at once.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] x86emul: special case far branch validation outside of long mode
2016-04-21 8:36 ` Andrew Cooper
@ 2016-04-21 8:55 ` Jan Beulich
2016-04-22 10:07 ` Wei Liu
0 siblings, 1 reply; 4+ messages in thread
From: Jan Beulich @ 2016-04-21 8:55 UTC (permalink / raw)
To: Wei Liu; +Cc: Andrew Cooper, Keir Fraser, xen-devel
>>> On 21.04.16 at 10:36, <andrew.cooper3@citrix.com> wrote:
> On 11/03/16 16:01, Jan Beulich wrote:
>> In that case (with the new value being held in, or now in one case cast
>> to, a 32-bit variable) there's no need to go through the long mode part
>> of the checks.
>>
>> Primarily this was meant to hopefully address Coverity ID 1355278, but
>> since the change produces smaller code as well I think we should use it
>> even if it doesn't help that (benign) warning.
>>
>> Also it's more in line with jmp_rel() for commit_far_branch() to do the
>> _regs.eip update, so adjust that at once.
>>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>
> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Wei,
considering that this at least attempts to address a Coverity issue,
I'd like to ask for this to be considered to be allowed in despite
being past code freeze.
Thanks, Jan
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] x86emul: special case far branch validation outside of long mode
2016-04-21 8:55 ` Jan Beulich
@ 2016-04-22 10:07 ` Wei Liu
0 siblings, 0 replies; 4+ messages in thread
From: Wei Liu @ 2016-04-22 10:07 UTC (permalink / raw)
To: Jan Beulich; +Cc: Andrew Cooper, Keir Fraser, Wei Liu, xen-devel
On Thu, Apr 21, 2016 at 02:55:33AM -0600, Jan Beulich wrote:
> >>> On 21.04.16 at 10:36, <andrew.cooper3@citrix.com> wrote:
> > On 11/03/16 16:01, Jan Beulich wrote:
> >> In that case (with the new value being held in, or now in one case cast
> >> to, a 32-bit variable) there's no need to go through the long mode part
> >> of the checks.
> >>
> >> Primarily this was meant to hopefully address Coverity ID 1355278, but
> >> since the change produces smaller code as well I think we should use it
> >> even if it doesn't help that (benign) warning.
> >>
> >> Also it's more in line with jmp_rel() for commit_far_branch() to do the
> >> _regs.eip update, so adjust that at once.
> >>
> >> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> >
> > Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
>
> Wei,
>
> considering that this at least attempts to address a Coverity issue,
> I'd like to ask for this to be considered to be allowed in despite
> being past code freeze.
>
> Thanks, Jan
>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>
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^ permalink raw reply [flat|nested] 4+ messages in thread
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2016-03-11 16:01 [PATCH] x86emul: special case far branch validation outside of long mode Jan Beulich
2016-04-21 8:36 ` Andrew Cooper
2016-04-21 8:55 ` Jan Beulich
2016-04-22 10:07 ` Wei Liu
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