From 2168285ffb30716f30e129c3ce98ce42d19c4d4e Mon Sep 17 00:00:00 2001
From: Stephan Baerwolf <***@tu-ilmenau.de>
Date: Sun, 8 Jan 2012 02:03:47 +0000
Subject: [PATCH 2/2] KVM: fix missing "illegal instruction"-trap in
protected modes
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.
(Therefore using Intel's "Intel 64 and IA-32 Architecture Software
Developers Manual" http://www.intel.com/content/dam/doc/manual/
64-ia-32-architectures-software-developer-manual-325462.pdf
and AMD's "AMD64 Architecture Programmer's Manual Volume 3:
General-Purpose and System Instructions"
http://support.amd.com/us/Processor_TechDocs/APM_V3_24594.pdf )
Screenshots of an i686 testing VM (CORE i5 host) before
and after applying this patch are available under:
Loading Image...
Loading Image...
Signed-off-by: Stephan Baerwolf <***@tu-ilmenau.de>
---
arch/x86/include/asm/kvm_emulate.h | 15 ++++++
arch/x86/kvm/emulate.c | 92
++++++++++++++++++++++++++++++++++-
2 files changed, 104 insertions(+), 3 deletions(-)
diff --git a/arch/x86/include/asm/kvm_emulate.h
b/arch/x86/include/asm/kvm_emulate.h
index b172bf4..5b68c23 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -301,6 +301,21 @@ 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_AMDisbetter_ebx 0x69444d41
+#define X86EMUL_CPUID_VENDOR_AMDisbetter_ecx 0x21726574
+#define X86EMUL_CPUID_VENDOR_AMDisbetter_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 f1e3be1..3357411 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1877,6 +1877,94 @@ setup_syscalls_segments(struct x86_emulate_ctxt
*ctxt,
ss->p = 1;
}
+static bool em_syscall_isenabled(struct x86_emulate_ctxt *ctxt)
+{
+ struct x86_emulate_ops *ops = ctxt->ops;
+ u64 efer = 0;
+
+ /* syscall is not available in real mode */
+ if ((ctxt->mode == X86EMUL_MODE_REAL) ||
+ (ctxt->mode == X86EMUL_MODE_VM86))
+ return false;
+
+ ops->get_msr(ctxt, MSR_EFER, &efer);
+ /* check - if guestOS is aware of syscall (0x0f05) */
+ if ((efer & EFER_SCE) == 0) {
+ return false;
+ } else {
+ /* ok, at this point it becomes vendor-specific */
+ /* so first get us an cpuid */
+ bool vendor;
+ u32 eax, ebx, ecx, edx;
+
+ /* getting the cpu-vendor */
+ eax = 0x00000000;
+ ecx = 0x00000000;
+ if (likely(ops->get_cpuid))
+ vendor = ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx);
+ else vendor = false;
+
+ if (likely(vendor)) {
+
+ /* AMD AuthenticAMD / AMDisbetter! */
+ if (((ebx==X86EMUL_CPUID_VENDOR_AuthenticAMD_ebx) &&
+ (ecx==X86EMUL_CPUID_VENDOR_AuthenticAMD_ecx) &&
+ (edx==X86EMUL_CPUID_VENDOR_AuthenticAMD_edx)) ||
+ ((ebx==X86EMUL_CPUID_VENDOR_AMDisbetter_ebx) &&
+ (ecx==X86EMUL_CPUID_VENDOR_AMDisbetter_ecx) &&
+ (edx==X86EMUL_CPUID_VENDOR_AMDisbetter_edx))) {
+
+ /* if cpu is not in longmode... */
+ /* ...check edx bit11 of cpuid 0x80000001 */
+ if (ctxt->mode != X86EMUL_MODE_PROT64) {
+ eax = 0x80000001;
+ ecx = 0x00000000;
+ vendor = ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx);
+ if (likely(vendor)) {
+ if (unlikely(((edx >> 11) & 0x1) == 0))
+ return false;
+ } else {
+ return false; /* assuming there is no bit 11 */
+ }
+ }
+ goto __em_syscall_enabled_noprotest;
+ } /* end "AMD" */
+
+
+ /* Intel (GenuineIntel) */
+ /* remarks: Intel CPUs only support "syscall" in 64bit longmode */
+ /* Also an 64bit guest within a 32bit compat-app running*/
+ /* will #UD !! */
+ /* While this behaviour can be fixed (by emulating) into*/
+ /* an AMD response - CPUs of AMD can't behave like Intel*/
+ /* because without an hardware-raised #UD there is no */
+ /* call in em.-mode (see x86_emulate_instruction(...))! */
+ /* TODO: make AMD-behaviour configurable */
+ if ((ebx==X86EMUL_CPUID_VENDOR_GenuineIntel_ebx) &&
+ (ecx==X86EMUL_CPUID_VENDOR_GenuineIntel_ecx) &&
+ (edx==X86EMUL_CPUID_VENDOR_GenuineIntel_edx)) {
+ if (ctxt->mode != X86EMUL_MODE_PROT64)
+ return false;
+ goto __em_syscall_enabled_noprotest;
+ } /* end "Intel" */
+
+ } /* end vendor is true */
+
+ } /* end MSR_EFER check */
+
+ /* default: */
+ /* this code wasn't able to process vendor */
+ /* so apply Intels stricter rules... */
+ pr_err_ratelimited("kvm: %i: unknown vcpu vendor - assuming
intel\n",
+ current->tgid);
+
+ if (ctxt->mode == X86EMUL_MODE_PROT64) goto
__em_syscall_enabled_noprotest;
+ return false;
+
+__em_syscall_enabled_noprotest:
+ return true;
+}
+
static int em_syscall(struct x86_emulate_ctxt *ctxt)
{
struct x86_emulate_ops *ops = ctxt->ops;
@@ -1885,9 +1973,7 @@ static int em_syscall(struct x86_emulate_ctxt *ctxt)
u16 cs_sel, ss_sel;
u64 efer = 0;
- /* syscall is not available in real mode */
- if (ctxt->mode == X86EMUL_MODE_REAL ||
- ctxt->mode == X86EMUL_MODE_VM86)
+ if (!(em_syscall_isenabled(ctxt)))
return emulate_ud(ctxt);
ops->get_msr(ctxt, MSR_EFER, &efer);
--
1.7.3.4
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