linux-kernel - [PATCH 3.2 151/152] KVM: x86 emulator: reject SYSENTER in compatibility mode on AMD guests

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Message-ID: <lsq.1424137613.67297861@decadent.org.uk>
Date:	Tue, 17 Feb 2015 01:46:53 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Avi Kivity" <avi@...hat.com>
Subject: [PATCH 3.2 151/152] KVM: x86 emulator: reject SYSENTER in
 compatibility mode on AMD guests

3.2.67-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Avi Kivity <avi@...hat.com>

commit 1a18a69b762374c423305772500f36eb8984ca52 upstream.

If the guest thinks it's an AMD, it will not have prepared the SYSENTER MSRs,
and if the guest executes SYSENTER in compatibility mode, it will fails.

Detect this condition and #UD instead, like the spec says.

Signed-off-by: Avi Kivity <avi@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kvm/emulate.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1952,6 +1952,17 @@ setup_syscalls_segments(struct x86_emula
 	ss->p = 1;
 }
 
+static bool vendor_intel(struct x86_emulate_ctxt *ctxt)
+{
+	u32 eax, ebx, ecx, edx;
+
+	eax = ecx = 0;
+	return ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx)
+		&& ebx == X86EMUL_CPUID_VENDOR_GenuineIntel_ebx
+		&& ecx == X86EMUL_CPUID_VENDOR_GenuineIntel_ecx
+		&& edx == X86EMUL_CPUID_VENDOR_GenuineIntel_edx;
+}
+
 static bool em_syscall_is_enabled(struct x86_emulate_ctxt *ctxt)
 {
 	struct x86_emulate_ops *ops = ctxt->ops;
@@ -2068,6 +2079,14 @@ static int em_sysenter(struct x86_emulat
 	if (ctxt->mode == X86EMUL_MODE_REAL)
 		return emulate_gp(ctxt, 0);
 
+	/*
+	 * Not recognized on AMD in compat mode (but is recognized in legacy
+	 * mode).
+	 */
+	if ((ctxt->mode == X86EMUL_MODE_PROT32) && (efer & EFER_LMA)
+	    && !vendor_intel(ctxt))
+		return emulate_ud(ctxt);
+
 	/* XXX sysenter/sysexit have not been tested in 64bit mode.
 	* Therefore, we inject an #UD.
 	*/

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