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authorStephan Bärwolf <stephan.baerwolf@tu-ilmenau.de>2012-01-12 16:43:04 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-04-02 09:27:13 -0700
commit35447aeacbe88ebbb30913b41f8e81f3135c79d9 (patch)
tree3879536ebb4987dc3c577dbf66cd18443dddbef0
parent0f06e7442a9d2035742189d05c3cdfd2b9dc47fd (diff)
KVM: x86: fix missing checks in syscall emulation
commit c2226fc9e87ba3da060e47333657cd6616652b84 upstream. On hosts without this patch, 32bit guests will crash (and 64bit guests may behave in a wrong way) for example by simply executing following nasm-demo-application: [bits 32] global _start SECTION .text _start: syscall (I tested it with winxp and linux - both always crashed) Disassembly of section .text: 00000000 <_start>: 0: 0f 05 syscall The reason seems a missing "invalid opcode"-trap (int6) for the syscall opcode "0f05", which is not available on Intel CPUs within non-longmodes, as also on some AMD CPUs within legacy-mode. (depending on CPU vendor, MSR_EFER and cpuid) Because previous mentioned OSs may not engage corresponding syscall target-registers (STAR, LSTAR, CSTAR), they remain NULL and (non trapping) syscalls are leading to multiple faults and finally crashs. Depending on the architecture (AMD or Intel) pretended by guests, various checks according to vendor's documentation are implemented to overcome the current issue and behave like the CPUs physical counterparts. [mtosatti: cleanup/beautify code] Signed-off-by: Stephan Baerwolf <stephan.baerwolf@tu-ilmenau.de> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com> Signed-off-by: Stefan Bader <stefan.bader@canonical.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--arch/x86/include/asm/kvm_emulate.h13
-rw-r--r--arch/x86/kvm/emulate.c51
2 files changed, 64 insertions, 0 deletions
diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index 18e54f1ec4e..0ab6a4dcb91 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -301,6 +301,19 @@ struct x86_emulate_ctxt {
#define X86EMUL_MODE_PROT (X86EMUL_MODE_PROT16|X86EMUL_MODE_PROT32| \
X86EMUL_MODE_PROT64)
+/* CPUID vendors */
+#define X86EMUL_CPUID_VENDOR_AuthenticAMD_ebx 0x68747541
+#define X86EMUL_CPUID_VENDOR_AuthenticAMD_ecx 0x444d4163
+#define X86EMUL_CPUID_VENDOR_AuthenticAMD_edx 0x69746e65
+
+#define X86EMUL_CPUID_VENDOR_AMDisbetterI_ebx 0x69444d41
+#define X86EMUL_CPUID_VENDOR_AMDisbetterI_ecx 0x21726574
+#define X86EMUL_CPUID_VENDOR_AMDisbetterI_edx 0x74656273
+
+#define X86EMUL_CPUID_VENDOR_GenuineIntel_ebx 0x756e6547
+#define X86EMUL_CPUID_VENDOR_GenuineIntel_ecx 0x6c65746e
+#define X86EMUL_CPUID_VENDOR_GenuineIntel_edx 0x49656e69
+
enum x86_intercept_stage {
X86_ICTP_NONE = 0, /* Allow zero-init to not match anything */
X86_ICPT_PRE_EXCEPT,
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index adc98675cda..3e7d9138dd2 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1901,6 +1901,51 @@ setup_syscalls_segments(struct x86_emulate_ctxt *ctxt,
ss->p = 1;
}
+static bool em_syscall_is_enabled(struct x86_emulate_ctxt *ctxt)
+{
+ struct x86_emulate_ops *ops = ctxt->ops;
+ u32 eax, ebx, ecx, edx;
+
+ /*
+ * syscall should always be enabled in longmode - so only become
+ * vendor specific (cpuid) if other modes are active...
+ */
+ if (ctxt->mode == X86EMUL_MODE_PROT64)
+ return true;
+
+ eax = 0x00000000;
+ ecx = 0x00000000;
+ if (ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx)) {
+ /*
+ * Intel ("GenuineIntel")
+ * remark: Intel CPUs only support "syscall" in 64bit
+ * longmode. Also an 64bit guest with a
+ * 32bit compat-app running will #UD !! While this
+ * behaviour can be fixed (by emulating) into AMD
+ * response - CPUs of AMD can't behave like Intel.
+ */
+ if (ebx == X86EMUL_CPUID_VENDOR_GenuineIntel_ebx &&
+ ecx == X86EMUL_CPUID_VENDOR_GenuineIntel_ecx &&
+ edx == X86EMUL_CPUID_VENDOR_GenuineIntel_edx)
+ return false;
+
+ /* AMD ("AuthenticAMD") */
+ if (ebx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ebx &&
+ ecx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ecx &&
+ edx == X86EMUL_CPUID_VENDOR_AuthenticAMD_edx)
+ return true;
+
+ /* AMD ("AMDisbetter!") */
+ if (ebx == X86EMUL_CPUID_VENDOR_AMDisbetterI_ebx &&
+ ecx == X86EMUL_CPUID_VENDOR_AMDisbetterI_ecx &&
+ edx == X86EMUL_CPUID_VENDOR_AMDisbetterI_edx)
+ return true;
+ }
+
+ /* default: (not Intel, not AMD), apply Intel's stricter rules... */
+ return false;
+}
+
static int
emulate_syscall(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
{
@@ -1915,9 +1960,15 @@ emulate_syscall(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
ctxt->mode == X86EMUL_MODE_VM86)
return emulate_ud(ctxt);
+ if (!(em_syscall_is_enabled(ctxt)))
+ return emulate_ud(ctxt);
+
ops->get_msr(ctxt, MSR_EFER, &efer);
setup_syscalls_segments(ctxt, ops, &cs, &ss);
+ if (!(efer & EFER_SCE))
+ return emulate_ud(ctxt);
+
ops->get_msr(ctxt, MSR_STAR, &msr_data);
msr_data >>= 32;
cs_sel = (u16)(msr_data & 0xfffc);