KVM: Fix stack-out-of-bounds read in write_mmio

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 3.2:
 - Drop ARM changes
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4baab231292f6f5745c83af5eca1de26bd6b2a3e..7e6094b0308b42f3976b5636339e342218b1ef60 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3920,7 +3920,7 @@ static int vcpu_mmio_read(struct kvm_vcpu *vcpu, gpa_t addr, int len, void *v)
                      !kvm_iodevice_read(&vcpu->arch.apic->dev, addr, n, v))
                    && kvm_io_bus_read(vcpu->kvm, 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;
@@ -4152,7 +4152,7 @@ static int read_prepare(struct kvm_vcpu *vcpu, void *val, int bytes)
        if (vcpu->mmio_read_completed) {
                memcpy(val, vcpu->mmio_data, bytes);
                trace_kvm_mmio(KVM_TRACE_MMIO_READ, bytes,
-                              vcpu->mmio_phys_addr, *(u64 *)val);
+                              vcpu->mmio_phys_addr, val);
                vcpu->mmio_read_completed = 0;
                return 1;
        }
@@ -4174,14 +4174,14 @@ 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 46e3cd8e197a54d2616bf8d3587b525d5f438f16..215a904f5e41c7534b8ef56e2f6ff330f2569b39 100644 (file)
--- a/include/trace/events/kvm.h
+++ b/include/trace/events/kvm.h
@@ -152,7 +152,7 @@ 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(
@@ -166,7 +166,10 @@ 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",