[Xen-devel] [PATCH] x86/emul: Avoid #UD in SIMD stubs

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

v{,u}comis{s,d}, and vcvt{,t}s{s,d}2si are two-operand instructions, while
vzero{all,upper} take no operands, so require vex.reg set to ~0 to avoid #UD.

Spotted while fuzzing with AFL
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
---
 xen/arch/x86/x86_emulate/x86_emulate.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c 
b/xen/arch/x86/x86_emulate/x86_emulate.c
index e09975c..8134e76 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -5620,7 +5620,7 @@ x86_emulate(
         {
             if ( ctxt->vendor == X86_VENDOR_AMD )
                 vex.l = 0;
-            generate_exception_if(vex.l, EXC_UD);
+            generate_exception_if(vex.l || vex.reg != 0xf, EXC_UD);
             host_and_vcpu_must_have(avx);
             get_fpu(X86EMUL_FPU_ymm, &fic);
         }
@@ -5673,6 +5673,7 @@ x86_emulate(
         }
         else
         {
+            generate_exception_if(vex.reg != 0xf, EXC_UD);
             host_and_vcpu_must_have(avx);
             get_fpu(X86EMUL_FPU_ymm, &fic);
         }
@@ -6273,6 +6274,7 @@ x86_emulate(
     case X86EMUL_OPC_VEX(0x0f, 0x77):    /* vzero{all,upper} */
         if ( vex.opcx != vex_none )
         {
+            generate_exception_if(vex.reg != 0xf, EXC_UD);
             host_and_vcpu_must_have(avx);
             get_fpu(X86EMUL_FPU_ymm, &fic);
         }
-- 
2.1.4


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