On 13/12/2017 15:12, Wanpeng Li wrote: > From: Wanpeng Li <[email protected]> > > 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 <[email protected]> > Cc: Paolo Bonzini <[email protected]> > Cc: Radim Krčmář <[email protected]> > Signed-off-by: Wanpeng Li <[email protected]> > --- > v1 -> v2: > * do the memcpy in kvm_mmio tracepoint > > arch/x86/kvm/x86.c | 6 +++--- > include/trace/events/kvm.h | 6 ++++-- > 2 files changed, 7 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 9212dad..4d1bc1a 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -4416,7 +4416,7 @@ 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; > @@ -4675,7 +4675,7 @@ 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; > } > @@ -4697,7 +4697,7 @@ 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); > } > > 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)); > ), > > TP_printk("mmio %s len %u gpa 0x%llx val 0x%llx", >
Looks good, thanks. Paolo
