Commit f3747379 authored by Nadav Amit's avatar Nadav Amit Committed by Paolo Bonzini
Browse files

KVM: x86: SYSENTER emulation is broken 



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: default avatarNadav Amit <namit@cs.technion.ac.il>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 63ea0a49

arch/x86/kvm/emulate.c

+8 −19
Original line number Diff line number Diff line
@@ -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;

	}



	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;

}

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