From: Pradeep Sawlani sawlani@google.com

commit e39d200fa5bf5b94a0948db0dae44c1b73b84a56 upstream.

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 leaks 5 bytes from the kernel stack (CVE-2017-17741). This patch fixes it by just accessing the bytes which we operate 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@google.com Reviewed-by: Darren Kenny darren.kenny@oracle.com Reviewed-by: Marc Zyngier marc.zyngier@arm.com Tested-by: Marc Zyngier marc.zyngier@arm.com Cc: Paolo Bonzini pbonzini@redhat.com Cc: Radim Krčmář rkrcmar@redhat.com Cc: Marc Zyngier marc.zyngier@arm.com Cc: Christoffer Dall christoffer.dall@linaro.org Signed-off-by: Wanpeng Li wanpeng.li@hotmail.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com [bwh: Backported to 4.4: -Adjust filename] Signed-off-by: Pradeep Sawlani sawlani@google.com --- arch/arm/kvm/mmio.c | 6 +++--- arch/x86/kvm/x86.c | 8 ++++---- include/trace/events/kvm.h | 7 +++++-- 3 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/arch/arm/kvm/mmio.c b/arch/arm/kvm/mmio.c index 3a10c9f1d0a4..387ee2a11e36 100644 --- a/arch/arm/kvm/mmio.c +++ b/arch/arm/kvm/mmio.c @@ -113,7 +113,7 @@ 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); } @@ -189,14 +189,14 @@ 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); 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); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index ccf17dbfea09..f973cfa8ff4f 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4114,7 +4114,7 @@ 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; @@ -4362,7 +4362,7 @@ 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; } @@ -4384,14 +4384,14 @@ 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 d6f83222a6a1..67ff6555967f 100644 --- a/include/trace/events/kvm.h +++ b/include/trace/events/kvm.h @@ -204,7 +204,7 @@ 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( @@ -218,7 +218,10 @@ 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_t(u32, sizeof(__entry->val), len)); ),

TP_printk("mmio %s len %u gpa 0x%llx val 0x%llx",