linux-kernel - [05/26] KVM: x86: remove vcpu's CPL check in host-invoked XCR set

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Message-ID: <lsq.1372214158.585208248@decadent.org.uk>
Date:	Wed, 26 Jun 2013 03:35:58 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Zhanghaoyu (A)" <haoyu.zhang@...wei.com>,
	"Paolo Bonzini" <pbonzini@...hat.com>
Subject: [05/26] KVM: x86: remove vcpu's CPL check in host-invoked XCR set

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

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

From: "Zhanghaoyu (A)" <haoyu.zhang@...wei.com>

commit 764bcbc5a6d7a2f3e75c9f0e4caa984e2926e346 upstream.

__kvm_set_xcr function does the CPL check when set xcr. __kvm_set_xcr is
called in two flows, one is invoked by guest, call stack shown as below,

  handle_xsetbv(or xsetbv_interception)
    kvm_set_xcr
      __kvm_set_xcr

the other one is invoked by host, for example during system reset:

  kvm_arch_vcpu_ioctl
    kvm_vcpu_ioctl_x86_set_xcrs
      __kvm_set_xcr

The former does need the CPL check, but the latter does not.

Signed-off-by: Zhang Haoyu <haoyu.zhang@...wei.com>
[Tweaks to commit message. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/kvm/x86.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -551,8 +551,6 @@ int __kvm_set_xcr(struct kvm_vcpu *vcpu,
 	if (index != XCR_XFEATURE_ENABLED_MASK)
 		return 1;
 	xcr0 = xcr;
-	if (kvm_x86_ops->get_cpl(vcpu) != 0)
-		return 1;
 	if (!(xcr0 & XSTATE_FP))
 		return 1;
 	if ((xcr0 & XSTATE_YMM) && !(xcr0 & XSTATE_SSE))
@@ -566,7 +564,8 @@ int __kvm_set_xcr(struct kvm_vcpu *vcpu,
 
 int kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
 {
-	if (__kvm_set_xcr(vcpu, index, xcr)) {
+	if (kvm_x86_ops->get_cpl(vcpu) != 0 ||
+	    __kvm_set_xcr(vcpu, index, xcr)) {
 		kvm_inject_gp(vcpu, 0);
 		return 1;
 	}

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