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Patch "KVM: x86: SYSENTER emulation is broken" has been added to the 3.10-stable tree

PATCH [email protected] 1 participant 1 message Apr 26, 2015

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This is a note to let you know that I've just added the patch titled

KVM: x86: SYSENTER emulation is broken

to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-x86-sysenter-emulation-is-broken.patch
and it can be found in the queue-3.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From f3747379accba8e95d70cec0eae0582c8c182050 Mon Sep 17 00:00:00 2001

From: Nadav Amit <[email protected]>
Date: Thu, 1 Jan 2015 23:11:11 +0200
Subject: KVM: x86: SYSENTER emulation is broken

From: Nadav Amit <[email protected]>

commit f3747379accba8e95d70cec0eae0582c8c182050 upstream.

SYSENTER emulation is broken in several ways:
1. It misses the case of 16-bit code segments completely (CVE-2015-0239).
2. MSR_IA32_SYSENTER_CS is checked in 64-bit mode incorrectly (bits 0 and 1 can still be set without causing #GP).
3. MSR_IA32_SYSENTER_EIP and MSR_IA32_SYSENTER_ESP are not masked in legacy-mode.
4. There is some unneeded code.

Fix it.

Signed-off-by Nadav Amit <[email protected]>
Signed-off-by Paolo Bonzini <[email protected]>

[zhangzhiqiang: backport to 3.10:
- adjust context
- in 3.10 context "ctxt->eflags &= ~(EFLG_VM | EFLG_IF | EFLG_RF)" is replaced by "ctxt->eflags &= ~(EFLG_VM | EFLG_IF)" in upstream, which was changed by another commit.
- After the above adjustments, becomes same to the original patch:

       https://github.com/torvalds/linux/commit/f3747379accba8e95d70cec0eae0582c8c182050

]

Signed-off-by Zhiqiang Zhang <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 arch/x86/kvm/emulate.c |   27 ++++++++-------------------
 1 file changed, 8 insertions(+), 19 deletions(-)
arch/x86/kvm/emulate.c +8 -19
@@ -2450,7 +2450,7 @@ static int em_sysenter(struct x86_emulat
 	 * Not recognized on AMD in compat mode (but is recognized in legacy
 	 * mode).
 	 */
-	if ((ctxt->mode == X86EMUL_MODE_PROT32) && (efer & EFER_LMA)
+	if ((ctxt->mode != X86EMUL_MODE_PROT64) && (efer & EFER_LMA)
 	    && !vendor_intel(ctxt))
 		return emulate_ud(ctxt);
 

@@ -2463,25 +2463,13 @@ static int em_sysenter(struct x86_emulat
 	setup_syscalls_segments(ctxt, &cs, &ss);
 
 	ops->get_msr(ctxt, MSR_IA32_SYSENTER_CS, &msr_data);
-	switch (ctxt->mode) {
-	case X86EMUL_MODE_PROT32:
-		if ((msr_data & 0xfffc) == 0x0)
-			return emulate_gp(ctxt, 0);
-		break;
-	case X86EMUL_MODE_PROT64:
-		if (msr_data == 0x0)
-			return emulate_gp(ctxt, 0);
-		break;
-	default:
-		break;
-	}
+	if ((msr_data & 0xfffc) == 0x0)
+		return emulate_gp(ctxt, 0);
 
 	ctxt->eflags &= ~(EFLG_VM | EFLG_IF | EFLG_RF);
-	cs_sel = (u16)msr_data;
-	cs_sel &= ~SELECTOR_RPL_MASK;
+	cs_sel = (u16)msr_data & ~SELECTOR_RPL_MASK;
 	ss_sel = cs_sel + 8;
-	ss_sel &= ~SELECTOR_RPL_MASK;
-	if (ctxt->mode == X86EMUL_MODE_PROT64 || (efer & EFER_LMA)) {
+	if (efer & EFER_LMA) {
 		cs.d = 0;
 		cs.l = 1;
 	}

@@ -2490,10 +2478,11 @@ static int em_sysenter(struct x86_emulat
 	ops->set_segment(ctxt, ss_sel, &ss, 0, VCPU_SREG_SS);
 
 	ops->get_msr(ctxt, MSR_IA32_SYSENTER_EIP, &msr_data);
-	ctxt->_eip = msr_data;
+	ctxt->_eip = (efer & EFER_LMA) ? msr_data : (u32)msr_data;
 
 	ops->get_msr(ctxt, MSR_IA32_SYSENTER_ESP, &msr_data);
-	*reg_write(ctxt, VCPU_REGS_RSP) = msr_data;
+	*reg_write(ctxt, VCPU_REGS_RSP) = (efer & EFER_LMA) ? msr_data :
+							      (u32)msr_data;
 
 	return X86EMUL_CONTINUE;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-3.10/kvm-x86-sysenter-emulation-is-broken.patch