x86emul: fix FXRSTOR test for most AMD CPUs
diff mbox series

Message ID 29986a8f-47bf-43c2-98e9-e08c1c5925af@suse.com
State New
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Series
  • x86emul: fix FXRSTOR test for most AMD CPUs
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Commit Message

Jan Beulich July 6, 2020, 3:14 p.m. UTC
AMD CPUs that we classify as X86_BUG_FPU_PTRS don't touch the selector/
offset portion of the save image during FXSAVE unless an unmasked
exception is pending. Hence the selector zapping done between the
initial FXSAVE and the emulated FXRSTOR needs to be mirrored onto the
second FXSAVE, output of which gets fed into memcmp() to compare with
the input image.

Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>

Comments

Andrew Cooper July 6, 2020, 3:46 p.m. UTC | #1
On 06/07/2020 16:14, Jan Beulich wrote:
> AMD CPUs that we classify as X86_BUG_FPU_PTRS don't touch the selector/
> offset portion of the save image during FXSAVE unless an unmasked
> exception is pending. Hence the selector zapping done between the
> initial FXSAVE and the emulated FXRSTOR needs to be mirrored onto the
> second FXSAVE, output of which gets fed into memcmp() to compare with
> the input image.
>
> Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Tested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Paul Durrant July 6, 2020, 3:56 p.m. UTC | #2
> -----Original Message-----
> From: Andrew Cooper <andrew.cooper3@citrix.com>
> Sent: 06 July 2020 16:47
> To: Jan Beulich <jbeulich@suse.com>; xen-devel@lists.xenproject.org
> Cc: Wei Liu <wl@xen.org>; Roger Pau Monné <roger.pau@citrix.com>; Paul Durrant <paul@xen.org>
> Subject: Re: [PATCH] x86emul: fix FXRSTOR test for most AMD CPUs
> 
> On 06/07/2020 16:14, Jan Beulich wrote:
> > AMD CPUs that we classify as X86_BUG_FPU_PTRS don't touch the selector/
> > offset portion of the save image during FXSAVE unless an unmasked
> > exception is pending. Hence the selector zapping done between the
> > initial FXSAVE and the emulated FXRSTOR needs to be mirrored onto the
> > second FXSAVE, output of which gets fed into memcmp() to compare with
> > the input image.
> >
> > Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
> > Signed-off-by: Jan Beulich <jbeulich@suse.com>
> 
> Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Tested-by: Andrew Cooper <andrew.cooper3@citrix.com>

Release-acked-by: Paul Durrant <paul@xen.org>

Patch
diff mbox series

--- a/tools/tests/x86_emulator/test_x86_emulator.c
+++ b/tools/tests/x86_emulator/test_x86_emulator.c
@@ -2577,6 +2577,7 @@  int main(int argc, char **argv)
         regs.ecx = (unsigned long)(res + 0x81);
         rc = x86_emulate(&ctxt, &emulops);
         asm volatile ( "fxsave %0" : "=m" (res[0x100]) :: "memory" );
+        zap_xfpsel(&res[0x100]);
         if ( (rc != X86EMUL_OKAY) ||
              memcmp(res + 0x100, res + 0x80, 0x200) ||
              (regs.eip != (unsigned long)&instr[4]) )