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KVM: Fix stack-out-of-bounds read in write_mmio
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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>
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@bonzini
Wanpeng Li authored and bonzini committed Dec 18, 2017
1 parent f298103 commit e39d200
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Showing 3 changed files with 12 additions and 9 deletions.
8 changes: 4 additions & 4 deletions arch/x86/kvm/x86.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -4384,7 +4384,7 @@ 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;
Expand Down Expand Up @@ -4643,7 +4643,7 @@ 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;
}
Expand All @@ -4665,14 +4665,14 @@ 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;
}

Expand Down
7 changes: 5 additions & 2 deletions include/trace/events/kvm.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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(
Expand All @@ -225,7 +225,10 @@ 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",
Expand Down
6 changes: 3 additions & 3 deletions virt/kvm/arm/mmio.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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);
}
Expand Down Expand Up @@ -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);
Expand Down

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