Re: [PATCH v4] KVM: Fix stack-out-of-bounds read in write_mmio
From: Wanpeng Li
Date: Sat Dec 16 2017 - 21:10:40 EST
2017-12-15 19:06 GMT+08:00 Marc Zyngier <marc.zyngier@xxxxxxx>:
> On 15/12/17 01:40, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>>
>> 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 <dvyukov@xxxxxxxxxx>
>> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>> Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
>> Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
>> Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
>> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>> ---
>> 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 <marc.zyngier@xxxxxxx>
> Tested-by: Marc Zyngier <marc.zyngier@xxxxxxx>
Thanks Marc. :)
Regards,
Wanpeng Li