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KVM: x86: Handle errors when RIP is set during far jumps
Far jmp/call/ret may fault while loading a new RIP. Currently KVM does not handle this case, and may result in failed vm-entry once the assignment is done. The tricky part of doing so is that loading the new CS affects the VMCS/VMCB state, so if we fail during loading the new RIP, we are left in unconsistent state. Therefore, this patch saves on 64-bit the old CS descriptor and restores it if loading RIP failed. This fixes CVE-2014-3647. Cc: stable@vger.kernel.org Signed-off-by: Nadav Amit <namit@cs.technion.ac.il> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
parent
234f3ce485
commit
d1442d85cc
1 changed files with 88 additions and 30 deletions
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@ -1443,7 +1443,9 @@ static int write_segment_descriptor(struct x86_emulate_ctxt *ctxt,
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/* Does not support long mode */
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static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
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u16 selector, int seg, u8 cpl, bool in_task_switch)
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u16 selector, int seg, u8 cpl,
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bool in_task_switch,
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struct desc_struct *desc)
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{
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struct desc_struct seg_desc, old_desc;
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u8 dpl, rpl;
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@ -1584,6 +1586,8 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
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}
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load:
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ctxt->ops->set_segment(ctxt, selector, &seg_desc, base3, seg);
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if (desc)
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*desc = seg_desc;
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return X86EMUL_CONTINUE;
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exception:
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return emulate_exception(ctxt, err_vec, err_code, true);
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@ -1593,7 +1597,7 @@ static int load_segment_descriptor(struct x86_emulate_ctxt *ctxt,
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u16 selector, int seg)
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{
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u8 cpl = ctxt->ops->cpl(ctxt);
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return __load_segment_descriptor(ctxt, selector, seg, cpl, false);
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return __load_segment_descriptor(ctxt, selector, seg, cpl, false, NULL);
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}
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static void write_register_operand(struct operand *op)
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@ -1987,17 +1991,31 @@ static int em_iret(struct x86_emulate_ctxt *ctxt)
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static int em_jmp_far(struct x86_emulate_ctxt *ctxt)
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{
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int rc;
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unsigned short sel;
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unsigned short sel, old_sel;
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struct desc_struct old_desc, new_desc;
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const struct x86_emulate_ops *ops = ctxt->ops;
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u8 cpl = ctxt->ops->cpl(ctxt);
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/* Assignment of RIP may only fail in 64-bit mode */
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if (ctxt->mode == X86EMUL_MODE_PROT64)
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ops->get_segment(ctxt, &old_sel, &old_desc, NULL,
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VCPU_SREG_CS);
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memcpy(&sel, ctxt->src.valptr + ctxt->op_bytes, 2);
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rc = load_segment_descriptor(ctxt, sel, VCPU_SREG_CS);
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rc = __load_segment_descriptor(ctxt, sel, VCPU_SREG_CS, cpl, false,
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&new_desc);
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if (rc != X86EMUL_CONTINUE)
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return rc;
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ctxt->_eip = 0;
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memcpy(&ctxt->_eip, ctxt->src.valptr, ctxt->op_bytes);
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return X86EMUL_CONTINUE;
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rc = assign_eip_far(ctxt, ctxt->src.val, new_desc.l);
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if (rc != X86EMUL_CONTINUE) {
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WARN_ON(!ctxt->mode != X86EMUL_MODE_PROT64);
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/* assigning eip failed; restore the old cs */
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ops->set_segment(ctxt, old_sel, &old_desc, 0, VCPU_SREG_CS);
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return rc;
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}
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return rc;
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}
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static int em_grp45(struct x86_emulate_ctxt *ctxt)
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@ -2064,21 +2082,34 @@ static int em_ret(struct x86_emulate_ctxt *ctxt)
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static int em_ret_far(struct x86_emulate_ctxt *ctxt)
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{
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int rc;
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unsigned long cs;
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unsigned long eip, cs;
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u16 old_cs;
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int cpl = ctxt->ops->cpl(ctxt);
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struct desc_struct old_desc, new_desc;
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const struct x86_emulate_ops *ops = ctxt->ops;
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rc = emulate_pop(ctxt, &ctxt->_eip, ctxt->op_bytes);
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if (ctxt->mode == X86EMUL_MODE_PROT64)
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ops->get_segment(ctxt, &old_cs, &old_desc, NULL,
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VCPU_SREG_CS);
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rc = emulate_pop(ctxt, &eip, ctxt->op_bytes);
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if (rc != X86EMUL_CONTINUE)
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return rc;
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if (ctxt->op_bytes == 4)
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ctxt->_eip = (u32)ctxt->_eip;
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rc = emulate_pop(ctxt, &cs, ctxt->op_bytes);
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if (rc != X86EMUL_CONTINUE)
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return rc;
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/* Outer-privilege level return is not implemented */
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if (ctxt->mode >= X86EMUL_MODE_PROT16 && (cs & 3) > cpl)
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return X86EMUL_UNHANDLEABLE;
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rc = load_segment_descriptor(ctxt, (u16)cs, VCPU_SREG_CS);
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rc = __load_segment_descriptor(ctxt, (u16)cs, VCPU_SREG_CS, 0, false,
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&new_desc);
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if (rc != X86EMUL_CONTINUE)
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return rc;
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rc = assign_eip_far(ctxt, eip, new_desc.l);
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if (rc != X86EMUL_CONTINUE) {
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WARN_ON(!ctxt->mode != X86EMUL_MODE_PROT64);
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ops->set_segment(ctxt, old_cs, &old_desc, 0, VCPU_SREG_CS);
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}
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return rc;
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}
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@ -2505,19 +2536,24 @@ static int load_state_from_tss16(struct x86_emulate_ctxt *ctxt,
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* Now load segment descriptors. If fault happens at this stage
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* it is handled in a context of new task
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*/
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ret = __load_segment_descriptor(ctxt, tss->ldt, VCPU_SREG_LDTR, cpl, true);
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ret = __load_segment_descriptor(ctxt, tss->ldt, VCPU_SREG_LDTR, cpl,
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true, NULL);
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if (ret != X86EMUL_CONTINUE)
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return ret;
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ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl, true);
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ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl,
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true, NULL);
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if (ret != X86EMUL_CONTINUE)
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return ret;
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ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl, true);
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ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl,
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true, NULL);
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if (ret != X86EMUL_CONTINUE)
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return ret;
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ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl, true);
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ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl,
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true, NULL);
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if (ret != X86EMUL_CONTINUE)
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return ret;
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ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl, true);
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ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl,
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true, NULL);
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if (ret != X86EMUL_CONTINUE)
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return ret;
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@ -2642,25 +2678,32 @@ static int load_state_from_tss32(struct x86_emulate_ctxt *ctxt,
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* Now load segment descriptors. If fault happenes at this stage
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* it is handled in a context of new task
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*/
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ret = __load_segment_descriptor(ctxt, tss->ldt_selector, VCPU_SREG_LDTR, cpl, true);
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ret = __load_segment_descriptor(ctxt, tss->ldt_selector, VCPU_SREG_LDTR,
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cpl, true, NULL);
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if (ret != X86EMUL_CONTINUE)
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return ret;
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ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl, true);
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ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl,
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true, NULL);
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if (ret != X86EMUL_CONTINUE)
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return ret;
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ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl, true);
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ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl,
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true, NULL);
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if (ret != X86EMUL_CONTINUE)
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return ret;
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ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl, true);
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ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl,
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true, NULL);
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if (ret != X86EMUL_CONTINUE)
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return ret;
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ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl, true);
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ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl,
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true, NULL);
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if (ret != X86EMUL_CONTINUE)
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return ret;
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ret = __load_segment_descriptor(ctxt, tss->fs, VCPU_SREG_FS, cpl, true);
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ret = __load_segment_descriptor(ctxt, tss->fs, VCPU_SREG_FS, cpl,
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true, NULL);
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if (ret != X86EMUL_CONTINUE)
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return ret;
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ret = __load_segment_descriptor(ctxt, tss->gs, VCPU_SREG_GS, cpl, true);
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ret = __load_segment_descriptor(ctxt, tss->gs, VCPU_SREG_GS, cpl,
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true, NULL);
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if (ret != X86EMUL_CONTINUE)
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return ret;
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@ -2942,24 +2985,39 @@ static int em_call_far(struct x86_emulate_ctxt *ctxt)
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u16 sel, old_cs;
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ulong old_eip;
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int rc;
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struct desc_struct old_desc, new_desc;
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const struct x86_emulate_ops *ops = ctxt->ops;
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int cpl = ctxt->ops->cpl(ctxt);
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old_cs = get_segment_selector(ctxt, VCPU_SREG_CS);
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old_eip = ctxt->_eip;
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ops->get_segment(ctxt, &old_cs, &old_desc, NULL, VCPU_SREG_CS);
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memcpy(&sel, ctxt->src.valptr + ctxt->op_bytes, 2);
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if (load_segment_descriptor(ctxt, sel, VCPU_SREG_CS))
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rc = __load_segment_descriptor(ctxt, sel, VCPU_SREG_CS, cpl, false,
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&new_desc);
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if (rc != X86EMUL_CONTINUE)
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return X86EMUL_CONTINUE;
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ctxt->_eip = 0;
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memcpy(&ctxt->_eip, ctxt->src.valptr, ctxt->op_bytes);
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rc = assign_eip_far(ctxt, ctxt->src.val, new_desc.l);
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if (rc != X86EMUL_CONTINUE)
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goto fail;
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ctxt->src.val = old_cs;
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rc = em_push(ctxt);
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if (rc != X86EMUL_CONTINUE)
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return rc;
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goto fail;
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ctxt->src.val = old_eip;
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return em_push(ctxt);
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rc = em_push(ctxt);
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/* If we failed, we tainted the memory, but the very least we should
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restore cs */
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if (rc != X86EMUL_CONTINUE)
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goto fail;
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return rc;
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fail:
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ops->set_segment(ctxt, old_cs, &old_desc, 0, VCPU_SREG_CS);
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return rc;
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}
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static int em_ret_near_imm(struct x86_emulate_ctxt *ctxt)
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