Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753868AbaKKLJ5 (ORCPT ); Tue, 11 Nov 2014 06:09:57 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:57362 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753796AbaKKLJw (ORCPT ); Tue, 11 Nov 2014 06:09:52 -0500 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Nadav Amit , Paolo Bonzini , Luis Henriques Subject: [PATCH 3.16.y-ckt 053/170] KVM: x86: Handle errors when RIP is set during far jumps Date: Tue, 11 Nov 2014 11:06:52 +0000 Message-Id: <1415704129-12709-54-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 2.1.0 In-Reply-To: <1415704129-12709-1-git-send-email-luis.henriques@canonical.com> References: <1415704129-12709-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.16 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.7-ckt1 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Nadav Amit commit d1442d85cc30ea75f7d399474ca738e0bc96f715 upstream. 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. Signed-off-by: Nadav Amit Signed-off-by: Paolo Bonzini [ luis: backported to 3.16: adjusted context ] Signed-off-by: Luis Henriques --- arch/x86/kvm/emulate.c | 118 ++++++++++++++++++++++++++++++++++++------------- 1 file changed, 88 insertions(+), 30 deletions(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 88bb0c20d31d..9a1946cb43c8 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -1439,7 +1439,9 @@ static int write_segment_descriptor(struct x86_emulate_ctxt *ctxt, /* Does not support long mode */ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt, - u16 selector, int seg, u8 cpl, bool in_task_switch) + u16 selector, int seg, u8 cpl, + bool in_task_switch, + struct desc_struct *desc) { struct desc_struct seg_desc, old_desc; u8 dpl, rpl; @@ -1568,6 +1570,8 @@ static int __load_segment_descriptor(struct x86_emulate_ctxt *ctxt, } load: ctxt->ops->set_segment(ctxt, selector, &seg_desc, 0, seg); + if (desc) + *desc = seg_desc; return X86EMUL_CONTINUE; exception: emulate_exception(ctxt, err_vec, err_code, true); @@ -1578,7 +1582,7 @@ static int load_segment_descriptor(struct x86_emulate_ctxt *ctxt, u16 selector, int seg) { u8 cpl = ctxt->ops->cpl(ctxt); - return __load_segment_descriptor(ctxt, selector, seg, cpl, false); + return __load_segment_descriptor(ctxt, selector, seg, cpl, false, NULL); } static void write_register_operand(struct operand *op) @@ -1975,17 +1979,31 @@ static int em_iret(struct x86_emulate_ctxt *ctxt) static int em_jmp_far(struct x86_emulate_ctxt *ctxt) { int rc; - unsigned short sel; + unsigned short sel, old_sel; + struct desc_struct old_desc, new_desc; + const struct x86_emulate_ops *ops = ctxt->ops; + u8 cpl = ctxt->ops->cpl(ctxt); + + /* Assignment of RIP may only fail in 64-bit mode */ + if (ctxt->mode == X86EMUL_MODE_PROT64) + ops->get_segment(ctxt, &old_sel, &old_desc, NULL, + VCPU_SREG_CS); memcpy(&sel, ctxt->src.valptr + ctxt->op_bytes, 2); - rc = load_segment_descriptor(ctxt, sel, VCPU_SREG_CS); + rc = __load_segment_descriptor(ctxt, sel, VCPU_SREG_CS, cpl, false, + &new_desc); if (rc != X86EMUL_CONTINUE) return rc; - ctxt->_eip = 0; - memcpy(&ctxt->_eip, ctxt->src.valptr, ctxt->op_bytes); - return X86EMUL_CONTINUE; + rc = assign_eip_far(ctxt, ctxt->src.val, new_desc.l); + if (rc != X86EMUL_CONTINUE) { + WARN_ON(!ctxt->mode != X86EMUL_MODE_PROT64); + /* assigning eip failed; restore the old cs */ + ops->set_segment(ctxt, old_sel, &old_desc, 0, VCPU_SREG_CS); + return rc; + } + return rc; } static int em_grp45(struct x86_emulate_ctxt *ctxt) @@ -2049,21 +2067,34 @@ static int em_ret(struct x86_emulate_ctxt *ctxt) static int em_ret_far(struct x86_emulate_ctxt *ctxt) { int rc; - unsigned long cs; + unsigned long eip, cs; + u16 old_cs; int cpl = ctxt->ops->cpl(ctxt); + struct desc_struct old_desc, new_desc; + const struct x86_emulate_ops *ops = ctxt->ops; + + if (ctxt->mode == X86EMUL_MODE_PROT64) + ops->get_segment(ctxt, &old_cs, &old_desc, NULL, + VCPU_SREG_CS); - rc = emulate_pop(ctxt, &ctxt->_eip, ctxt->op_bytes); + rc = emulate_pop(ctxt, &eip, ctxt->op_bytes); if (rc != X86EMUL_CONTINUE) return rc; - if (ctxt->op_bytes == 4) - ctxt->_eip = (u32)ctxt->_eip; rc = emulate_pop(ctxt, &cs, ctxt->op_bytes); if (rc != X86EMUL_CONTINUE) return rc; /* Outer-privilege level return is not implemented */ if (ctxt->mode >= X86EMUL_MODE_PROT16 && (cs & 3) > cpl) return X86EMUL_UNHANDLEABLE; - rc = load_segment_descriptor(ctxt, (u16)cs, VCPU_SREG_CS); + rc = __load_segment_descriptor(ctxt, (u16)cs, VCPU_SREG_CS, 0, false, + &new_desc); + if (rc != X86EMUL_CONTINUE) + return rc; + rc = assign_eip_far(ctxt, eip, new_desc.l); + if (rc != X86EMUL_CONTINUE) { + WARN_ON(!ctxt->mode != X86EMUL_MODE_PROT64); + ops->set_segment(ctxt, old_cs, &old_desc, 0, VCPU_SREG_CS); + } return rc; } @@ -2487,19 +2518,24 @@ static int load_state_from_tss16(struct x86_emulate_ctxt *ctxt, * Now load segment descriptors. If fault happens at this stage * it is handled in a context of new task */ - ret = __load_segment_descriptor(ctxt, tss->ldt, VCPU_SREG_LDTR, cpl, true); + ret = __load_segment_descriptor(ctxt, tss->ldt, VCPU_SREG_LDTR, cpl, + true, NULL); if (ret != X86EMUL_CONTINUE) return ret; - ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl, true); + ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl, + true, NULL); if (ret != X86EMUL_CONTINUE) return ret; - ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl, true); + ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl, + true, NULL); if (ret != X86EMUL_CONTINUE) return ret; - ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl, true); + ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl, + true, NULL); if (ret != X86EMUL_CONTINUE) return ret; - ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl, true); + ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl, + true, NULL); if (ret != X86EMUL_CONTINUE) return ret; @@ -2624,25 +2660,32 @@ static int load_state_from_tss32(struct x86_emulate_ctxt *ctxt, * Now load segment descriptors. If fault happenes at this stage * it is handled in a context of new task */ - ret = __load_segment_descriptor(ctxt, tss->ldt_selector, VCPU_SREG_LDTR, cpl, true); + ret = __load_segment_descriptor(ctxt, tss->ldt_selector, VCPU_SREG_LDTR, + cpl, true, NULL); if (ret != X86EMUL_CONTINUE) return ret; - ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl, true); + ret = __load_segment_descriptor(ctxt, tss->es, VCPU_SREG_ES, cpl, + true, NULL); if (ret != X86EMUL_CONTINUE) return ret; - ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl, true); + ret = __load_segment_descriptor(ctxt, tss->cs, VCPU_SREG_CS, cpl, + true, NULL); if (ret != X86EMUL_CONTINUE) return ret; - ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl, true); + ret = __load_segment_descriptor(ctxt, tss->ss, VCPU_SREG_SS, cpl, + true, NULL); if (ret != X86EMUL_CONTINUE) return ret; - ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl, true); + ret = __load_segment_descriptor(ctxt, tss->ds, VCPU_SREG_DS, cpl, + true, NULL); if (ret != X86EMUL_CONTINUE) return ret; - ret = __load_segment_descriptor(ctxt, tss->fs, VCPU_SREG_FS, cpl, true); + ret = __load_segment_descriptor(ctxt, tss->fs, VCPU_SREG_FS, cpl, + true, NULL); if (ret != X86EMUL_CONTINUE) return ret; - ret = __load_segment_descriptor(ctxt, tss->gs, VCPU_SREG_GS, cpl, true); + ret = __load_segment_descriptor(ctxt, tss->gs, VCPU_SREG_GS, cpl, + true, NULL); if (ret != X86EMUL_CONTINUE) return ret; @@ -2925,24 +2968,39 @@ static int em_call_far(struct x86_emulate_ctxt *ctxt) u16 sel, old_cs; ulong old_eip; int rc; + struct desc_struct old_desc, new_desc; + const struct x86_emulate_ops *ops = ctxt->ops; + int cpl = ctxt->ops->cpl(ctxt); - old_cs = get_segment_selector(ctxt, VCPU_SREG_CS); old_eip = ctxt->_eip; + ops->get_segment(ctxt, &old_cs, &old_desc, NULL, VCPU_SREG_CS); memcpy(&sel, ctxt->src.valptr + ctxt->op_bytes, 2); - if (load_segment_descriptor(ctxt, sel, VCPU_SREG_CS)) + rc = __load_segment_descriptor(ctxt, sel, VCPU_SREG_CS, cpl, false, + &new_desc); + if (rc != X86EMUL_CONTINUE) return X86EMUL_CONTINUE; - ctxt->_eip = 0; - memcpy(&ctxt->_eip, ctxt->src.valptr, ctxt->op_bytes); + rc = assign_eip_far(ctxt, ctxt->src.val, new_desc.l); + if (rc != X86EMUL_CONTINUE) + goto fail; ctxt->src.val = old_cs; rc = em_push(ctxt); if (rc != X86EMUL_CONTINUE) - return rc; + goto fail; ctxt->src.val = old_eip; - return em_push(ctxt); + rc = em_push(ctxt); + /* If we failed, we tainted the memory, but the very least we should + restore cs */ + if (rc != X86EMUL_CONTINUE) + goto fail; + return rc; +fail: + ops->set_segment(ctxt, old_cs, &old_desc, 0, VCPU_SREG_CS); + return rc; + } static int em_ret_near_imm(struct x86_emulate_ctxt *ctxt) -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/