[Xen-devel] [PATCH] libxc/restore: Fix REC_TYPE_X86_PV_VCPU_XSAVE data auditing (take 2)

[Xen-devel] [PATCH] libxc/restore: Fix REC_TYPE_X86_PV_VCPU_XSAVE data auditing (take 2)

[Andrew Cooper]

It turns out that a bug (since forever) in Xen causes XSAVE records to have
non-architectural behaviour on xsave-capable hardware, when a PV guest has not
touched the state.

In such a case, the data record returned from Xen is 2*uint64_t, both claiming
the (illegitimate) state of %xcr0 and %xcr0_accum being 0.

Adjust the bound in handle_x86_pv_vcpu_blob() to cope with this.

Fixes: 2a62c22715b "libxc/restore: Fix data auditing in handle_x86_pv_vcpu_blob()"
Reported-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Ian Jackson <Ian.Jackson@citrix.com>
CC: Wei Liu <wl@xen.org>
CC: Igor Druzhinin <igor.druzhinin@citrix.com>

I'll see about fixing Xen at some other point.  A second bug is that we have
two copies of part of the vCPU's FPU state.
---
 tools/libxc/xc_sr_restore_x86_pv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/libxc/xc_sr_restore_x86_pv.c b/tools/libxc/xc_sr_restore_x86_pv.c
index 16e738884e..904ccc462a 100644
--- a/tools/libxc/xc_sr_restore_x86_pv.c
+++ b/tools/libxc/xc_sr_restore_x86_pv.c
@@ -827,10 +827,10 @@ static int handle_x86_pv_vcpu_blob(struct xc_sr_context *ctx,
         break;
 
     case REC_TYPE_X86_PV_VCPU_XSAVE:
-        if ( blobsz < 128 )
+        if ( blobsz < 16 )
         {
             ERROR("%s record too short: min %zu, got %u",
-                  rec_name, sizeof(*vhdr) + 128, rec->length);
+                  rec_name, sizeof(*vhdr) + 16, rec->length);
             goto out;
         }
         blob = &vcpu->xsave;
-- 
2.11.0


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Re: [Xen-devel] [PATCH] libxc/restore: Fix REC_TYPE_X86_PV_VCPU_XSAVE data auditing (take 2)

[Wei Liu]

On Tue, Feb 04, 2020 at 08:29:38PM +0000, Andrew Cooper wrote:
> It turns out that a bug (since forever) in Xen causes XSAVE records to have
> non-architectural behaviour on xsave-capable hardware, when a PV guest has not
> touched the state.
> 
> In such a case, the data record returned from Xen is 2*uint64_t, both claiming
> the (illegitimate) state of %xcr0 and %xcr0_accum being 0.
> 
> Adjust the bound in handle_x86_pv_vcpu_blob() to cope with this.
> 
> Fixes: 2a62c22715b "libxc/restore: Fix data auditing in handle_x86_pv_vcpu_blob()"
> Reported-by: Igor Druzhinin <igor.druzhinin@citrix.com>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Acked-by: Wei Liu <wl@xen.org>

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