Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755161AbdLOLHG (ORCPT ); Fri, 15 Dec 2017 06:07:06 -0500 Received: from foss.arm.com ([217.140.101.70]:54236 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755011AbdLOLHC (ORCPT ); Fri, 15 Dec 2017 06:07:02 -0500 Subject: Re: [PATCH v4] KVM: Fix stack-out-of-bounds read in write_mmio To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Wanpeng Li , Christoffer Dall References: <1513302050-14253-1-git-send-email-wanpeng.li@hotmail.com> From: Marc Zyngier Organization: ARM Ltd Message-ID: <15b7b9e5-5b11-f20f-0260-5c8b9fc5e111@arm.com> Date: Fri, 15 Dec 2017 11:06:58 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <1513302050-14253-1-git-send-email-wanpeng.li@hotmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6099 Lines: 172 On 15/12/17 01:40, Wanpeng Li wrote: > From: Wanpeng Li > > Reported by syzkaller: > > BUG: KASAN: stack-out-of-bounds in write_mmio+0x11e/0x270 [kvm] > Read of size 8 at addr ffff8803259df7f8 by task syz-executor/32298 > > CPU: 6 PID: 32298 Comm: syz-executor Tainted: G OE 4.15.0-rc2+ #18 > Hardware name: LENOVO ThinkCentre M8500t-N000/SHARKBAY, BIOS FBKTC1AUS 02/16/2016 > Call Trace: > dump_stack+0xab/0xe1 > print_address_description+0x6b/0x290 > kasan_report+0x28a/0x370 > write_mmio+0x11e/0x270 [kvm] > emulator_read_write_onepage+0x311/0x600 [kvm] > emulator_read_write+0xef/0x240 [kvm] > emulator_fix_hypercall+0x105/0x150 [kvm] > em_hypercall+0x2b/0x80 [kvm] > x86_emulate_insn+0x2b1/0x1640 [kvm] > x86_emulate_instruction+0x39a/0xb90 [kvm] > handle_exception+0x1b4/0x4d0 [kvm_intel] > vcpu_enter_guest+0x15a0/0x2640 [kvm] > kvm_arch_vcpu_ioctl_run+0x549/0x7d0 [kvm] > kvm_vcpu_ioctl+0x479/0x880 [kvm] > do_vfs_ioctl+0x142/0x9a0 > SyS_ioctl+0x74/0x80 > entry_SYSCALL_64_fastpath+0x23/0x9a > > The path of patched vmmcall will patch 3 bytes opcode 0F 01 C1(vmcall) > to the guest memory, however, write_mmio tracepoint always prints 8 bytes > through *(u64 *)val since kvm splits the mmio access into 8 bytes. This > can result in stack-out-of-bounds read due to access the extra 5 bytes. > This patch fixes it by just accessing the bytes which we operates on. > > Before patch: > > syz-executor-5567 [007] .... 51370.561696: kvm_mmio: mmio write len 3 gpa 0x10 val 0x1ffff10077c1010f > > After patch: > > syz-executor-13416 [002] .... 51302.299573: kvm_mmio: mmio write len 3 gpa 0x10 val 0xc1010f > > Reported-by: Dmitry Vyukov > Cc: Paolo Bonzini > Cc: Radim Krčmář > Cc: Marc Zyngier > Cc: Christoffer Dall > Signed-off-by: Wanpeng Li > --- > v3 -> v4: > * fix the arm tracepoint > v2 -> v3: > * fix sparse warning > v1 -> v2: > * do the memcpy in kvm_mmio tracepoint > > arch/x86/kvm/x86.c | 8 ++++---- > include/trace/events/kvm.h | 6 ++++-- > virt/kvm/arm/mmio.c | 6 +++--- > 3 files changed, 11 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 0f82e2c..c7071e7 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -4456,7 +4456,7 @@ static int vcpu_mmio_read(struct kvm_vcpu *vcpu, gpa_t addr, int len, void *v) > addr, n, v)) > && kvm_io_bus_read(vcpu, KVM_MMIO_BUS, addr, n, v)) > break; > - trace_kvm_mmio(KVM_TRACE_MMIO_READ, n, addr, *(u64 *)v); > + trace_kvm_mmio(KVM_TRACE_MMIO_READ, n, addr, v); > handled += n; > addr += n; > len -= n; > @@ -4715,7 +4715,7 @@ static int read_prepare(struct kvm_vcpu *vcpu, void *val, int bytes) > { > if (vcpu->mmio_read_completed) { > trace_kvm_mmio(KVM_TRACE_MMIO_READ, bytes, > - vcpu->mmio_fragments[0].gpa, *(u64 *)val); > + vcpu->mmio_fragments[0].gpa, val); > vcpu->mmio_read_completed = 0; > return 1; > } > @@ -4737,14 +4737,14 @@ static int write_emulate(struct kvm_vcpu *vcpu, gpa_t gpa, > > static int write_mmio(struct kvm_vcpu *vcpu, gpa_t gpa, int bytes, void *val) > { > - trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, bytes, gpa, *(u64 *)val); > + trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, bytes, gpa, val); > return vcpu_mmio_write(vcpu, gpa, bytes, val); > } > > static int read_exit_mmio(struct kvm_vcpu *vcpu, gpa_t gpa, > void *val, int bytes) > { > - trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, bytes, gpa, 0); > + trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, bytes, gpa, NULL); > return X86EMUL_IO_NEEDED; > } > > diff --git a/include/trace/events/kvm.h b/include/trace/events/kvm.h > index e4b0b8e..dfd2170 100644 > --- a/include/trace/events/kvm.h > +++ b/include/trace/events/kvm.h > @@ -211,7 +211,7 @@ TRACE_EVENT(kvm_ack_irq, > { KVM_TRACE_MMIO_WRITE, "write" } > > TRACE_EVENT(kvm_mmio, > - TP_PROTO(int type, int len, u64 gpa, u64 val), > + TP_PROTO(int type, int len, u64 gpa, void *val), > TP_ARGS(type, len, gpa, val), > > TP_STRUCT__entry( > @@ -225,7 +225,9 @@ TRACE_EVENT(kvm_mmio, > __entry->type = type; > __entry->len = len; > __entry->gpa = gpa; > - __entry->val = val; > + __entry->val = 0; > + if (val) > + memcpy(&__entry->val, val, min(8, len)); I'm not fond of hardcoded sizes; they tend to break as people change the code around. Consider using sizeof(__entry->val) instead of 8. > ), > > TP_printk("mmio %s len %u gpa 0x%llx val 0x%llx", > diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c > index b6e715f..dac7ceb 100644 > --- a/virt/kvm/arm/mmio.c > +++ b/virt/kvm/arm/mmio.c > @@ -112,7 +112,7 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run) > } > > trace_kvm_mmio(KVM_TRACE_MMIO_READ, len, run->mmio.phys_addr, > - data); > + &data); > data = vcpu_data_host_to_guest(vcpu, data, len); > vcpu_set_reg(vcpu, vcpu->arch.mmio_decode.rt, data); > } > @@ -182,14 +182,14 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run, > data = vcpu_data_guest_to_host(vcpu, vcpu_get_reg(vcpu, rt), > len); > > - trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, len, fault_ipa, data); > + trace_kvm_mmio(KVM_TRACE_MMIO_WRITE, len, fault_ipa, &data); > kvm_mmio_write_buf(data_buf, len, data); > > ret = kvm_io_bus_write(vcpu, KVM_MMIO_BUS, fault_ipa, len, > data_buf); > } else { > trace_kvm_mmio(KVM_TRACE_MMIO_READ_UNSATISFIED, len, > - fault_ipa, 0); > + fault_ipa, NULL); > > ret = kvm_io_bus_read(vcpu, KVM_MMIO_BUS, fault_ipa, len, > data_buf); > I've given it a go on an arm64 platform, which works as expected. Assuming you address the above: Reviewed-by: Marc Zyngier Tested-by: Marc Zyngier Thanks, M. -- Jazz is not dead. It just smells funny...