Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753814AbaKAW43 (ORCPT ); Sat, 1 Nov 2014 18:56:29 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:60116 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751531AbaKAWj1 (ORCPT ); Sat, 1 Nov 2014 18:39:27 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Nadav Amit" , "Paolo Bonzini" Date: Sat, 01 Nov 2014 22:28:03 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 091/102] KVM: x86: Emulator fixes for eip canonical checks on near branches In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.64-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Nadav Amit commit 234f3ce485d54017f15cf5e0699cff4100121601 upstream. Before changing rip (during jmp, call, ret, etc.) the target should be asserted to be canonical one, as real CPUs do. During sysret, both target rsp and rip should be canonical. If any of these values is noncanonical, a #GP exception should occur. The exception to this rule are syscall and sysenter instructions in which the assigned rip is checked during the assignment to the relevant MSRs. This patch fixes the emulator to behave as real CPUs do for near branches. Far branches are handled by the next patch. This fixes CVE-2014-3647. Signed-off-by: Nadav Amit Signed-off-by: Paolo Bonzini [bwh: Backported to 3.2: - Adjust context - Use ctxt->regs[] instead of reg_read(), reg_write(), reg_rmw()] Signed-off-by: Ben Hutchings --- arch/x86/kvm/emulate.c | 78 ++++++++++++++++++++++++++++++++++---------------- 1 file changed, 54 insertions(+), 24 deletions(-) --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -529,7 +529,8 @@ static int emulate_nm(struct x86_emulate return emulate_exception(ctxt, NM_VECTOR, 0, false); } -static inline void assign_eip_near(struct x86_emulate_ctxt *ctxt, ulong dst) +static inline int assign_eip_far(struct x86_emulate_ctxt *ctxt, ulong dst, + int cs_l) { switch (ctxt->op_bytes) { case 2: @@ -539,16 +540,25 @@ static inline void assign_eip_near(struc ctxt->_eip = (u32)dst; break; case 8: + if ((cs_l && is_noncanonical_address(dst)) || + (!cs_l && (dst & ~(u32)-1))) + return emulate_gp(ctxt, 0); ctxt->_eip = dst; break; default: WARN(1, "unsupported eip assignment size\n"); } + return X86EMUL_CONTINUE; +} + +static inline int assign_eip_near(struct x86_emulate_ctxt *ctxt, ulong dst) +{ + return assign_eip_far(ctxt, dst, ctxt->mode == X86EMUL_MODE_PROT64); } -static inline void jmp_rel(struct x86_emulate_ctxt *ctxt, int rel) +static inline int jmp_rel(struct x86_emulate_ctxt *ctxt, int rel) { - assign_eip_near(ctxt, ctxt->_eip + rel); + return assign_eip_near(ctxt, ctxt->_eip + rel); } static u16 get_segment_selector(struct x86_emulate_ctxt *ctxt, unsigned seg) @@ -1787,13 +1797,15 @@ static int em_grp45(struct x86_emulate_c case 2: /* call near abs */ { long int old_eip; old_eip = ctxt->_eip; - ctxt->_eip = ctxt->src.val; + rc = assign_eip_near(ctxt, ctxt->src.val); + if (rc != X86EMUL_CONTINUE) + break; ctxt->src.val = old_eip; rc = em_push(ctxt); break; } case 4: /* jmp abs */ - ctxt->_eip = ctxt->src.val; + rc = assign_eip_near(ctxt, ctxt->src.val); break; case 5: /* jmp far */ rc = em_jmp_far(ctxt); @@ -1825,10 +1837,14 @@ static int em_grp9(struct x86_emulate_ct static int em_ret(struct x86_emulate_ctxt *ctxt) { - ctxt->dst.type = OP_REG; - ctxt->dst.addr.reg = &ctxt->_eip; - ctxt->dst.bytes = ctxt->op_bytes; - return em_pop(ctxt); + int rc; + unsigned long eip; + + rc = emulate_pop(ctxt, &eip, ctxt->op_bytes); + if (rc != X86EMUL_CONTINUE) + return rc; + + return assign_eip_near(ctxt, eip); } static int em_ret_far(struct x86_emulate_ctxt *ctxt) @@ -2060,7 +2076,7 @@ static int em_sysexit(struct x86_emulate { struct x86_emulate_ops *ops = ctxt->ops; struct desc_struct cs, ss; - u64 msr_data; + u64 msr_data, rcx, rdx; int usermode; u16 cs_sel = 0, ss_sel = 0; @@ -2076,6 +2092,9 @@ static int em_sysexit(struct x86_emulate else usermode = X86EMUL_MODE_PROT32; + rcx = ctxt->regs[VCPU_REGS_RCX]; + rdx = ctxt->regs[VCPU_REGS_RDX]; + cs.dpl = 3; ss.dpl = 3; ops->get_msr(ctxt, MSR_IA32_SYSENTER_CS, &msr_data); @@ -2093,6 +2112,9 @@ static int em_sysexit(struct x86_emulate ss_sel = cs_sel + 8; cs.d = 0; cs.l = 1; + if (is_noncanonical_address(rcx) || + is_noncanonical_address(rdx)) + return emulate_gp(ctxt, 0); break; } cs_sel |= SELECTOR_RPL_MASK; @@ -2101,8 +2123,8 @@ static int em_sysexit(struct x86_emulate ops->set_segment(ctxt, cs_sel, &cs, 0, VCPU_SREG_CS); ops->set_segment(ctxt, ss_sel, &ss, 0, VCPU_SREG_SS); - ctxt->_eip = ctxt->regs[VCPU_REGS_RDX]; - ctxt->regs[VCPU_REGS_RSP] = ctxt->regs[VCPU_REGS_RCX]; + ctxt->_eip = rdx; + ctxt->regs[VCPU_REGS_RSP] = rcx; return X86EMUL_CONTINUE; } @@ -2555,10 +2577,13 @@ static int em_das(struct x86_emulate_ctx static int em_call(struct x86_emulate_ctxt *ctxt) { + int rc; long rel = ctxt->src.val; ctxt->src.val = (unsigned long)ctxt->_eip; - jmp_rel(ctxt, rel); + rc = jmp_rel(ctxt, rel); + if (rc != X86EMUL_CONTINUE) + return rc; return em_push(ctxt); } @@ -2590,11 +2615,12 @@ static int em_call_far(struct x86_emulat static int em_ret_near_imm(struct x86_emulate_ctxt *ctxt) { int rc; + unsigned long eip; - ctxt->dst.type = OP_REG; - ctxt->dst.addr.reg = &ctxt->_eip; - ctxt->dst.bytes = ctxt->op_bytes; - rc = emulate_pop(ctxt, &ctxt->dst.val, ctxt->op_bytes); + rc = emulate_pop(ctxt, &eip, ctxt->op_bytes); + if (rc != X86EMUL_CONTINUE) + return rc; + rc = assign_eip_near(ctxt, eip); if (rc != X86EMUL_CONTINUE) return rc; register_address_increment(ctxt, &ctxt->regs[VCPU_REGS_RSP], ctxt->src.val); @@ -2840,20 +2866,24 @@ static int em_lmsw(struct x86_emulate_ct static int em_loop(struct x86_emulate_ctxt *ctxt) { + int rc = X86EMUL_CONTINUE; + register_address_increment(ctxt, &ctxt->regs[VCPU_REGS_RCX], -1); if ((address_mask(ctxt, ctxt->regs[VCPU_REGS_RCX]) != 0) && (ctxt->b == 0xe2 || test_cc(ctxt->b ^ 0x5, ctxt->eflags))) - jmp_rel(ctxt, ctxt->src.val); + rc = jmp_rel(ctxt, ctxt->src.val); - return X86EMUL_CONTINUE; + return rc; } static int em_jcxz(struct x86_emulate_ctxt *ctxt) { + int rc = X86EMUL_CONTINUE; + if (address_mask(ctxt, ctxt->regs[VCPU_REGS_RCX]) == 0) - jmp_rel(ctxt, ctxt->src.val); + rc = jmp_rel(ctxt, ctxt->src.val); - return X86EMUL_CONTINUE; + return rc; } static int em_cli(struct x86_emulate_ctxt *ctxt) @@ -3946,7 +3976,7 @@ special_insn: break; case 0x70 ... 0x7f: /* jcc (short) */ if (test_cc(ctxt->b, ctxt->eflags)) - jmp_rel(ctxt, ctxt->src.val); + rc = jmp_rel(ctxt, ctxt->src.val); break; case 0x8d: /* lea r16/r32, m */ ctxt->dst.val = ctxt->src.addr.mem.ea; @@ -3994,7 +4024,7 @@ special_insn: goto do_io_out; case 0xe9: /* jmp rel */ case 0xeb: /* jmp rel short */ - jmp_rel(ctxt, ctxt->src.val); + rc = jmp_rel(ctxt, ctxt->src.val); ctxt->dst.type = OP_NONE; /* Disable writeback. */ break; case 0xec: /* in al,dx */ @@ -4160,7 +4190,7 @@ twobyte_insn: break; case 0x80 ... 0x8f: /* jnz rel, etc*/ if (test_cc(ctxt->b, ctxt->eflags)) - jmp_rel(ctxt, ctxt->src.val); + rc = jmp_rel(ctxt, ctxt->src.val); break; case 0x90 ... 0x9f: /* setcc r/m8 */ ctxt->dst.val = test_cc(ctxt->b, ctxt->eflags); -- 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/