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KVM: x86: SYSENTER emulation is broken

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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.

Cc: stable@vger.linux.org
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Nadav Amit 2015-01-01 23:11:11 +02:00 committed by Paolo Bonzini
parent 63ea0a49ae
commit f3747379ac
1 changed files with 8 additions and 19 deletions
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27
arch/x86/kvm/emulate.c
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@ -2348,7 +2348,7 @@ static int em_sysenter(struct x86_emulate_ctxt *ctxt)
* 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);
@ -2359,25 +2359,13 @@ static int em_sysenter(struct x86_emulate_ctxt *ctxt)
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);
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;
}
@ -2386,10 +2374,11 @@ static int em_sysenter(struct x86_emulate_ctxt *ctxt)
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;
}