[Xenial][PATCH 0/1] CVE-2017-17741

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[Xenial][PATCH 0/1] CVE-2017-17741

Khalid Elmously
CVE-2017-17741


The KVM implementation in the Linux kernel through 4.14.7 allows attackers
to cause a denial of service (write_mmio stack-based out-of-bounds read) or
possibly have unspecified other impact, related to arch/x86/kvm/x86.c and
include/trace/events/kvm.h.

This was backported from upstream e39d200fa5bf5b94a0948db0dae44c1b73b84a56 with very minor changes - however different patches are needed for Trusty/Zesty/Artful so they will be in a different email thread.


Wanpeng Li  (1):
  KVM: Fix stack-out-of-bounds read in write_mmio

 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(-)

--
2.14.1


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[Xenial][PATCH 1/1] CVE-2017-17741 KVM: Fix stack-out-of-bounds read in write_mmio

Khalid Elmously
From: Wanpeng Li <[hidden email]>

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


(backported from e39d200fa5bf5b94a0948db0dae44c1b73b84a56)


CVE-2017-17741

References: CVE-2017-17741
Reported-by: Dmitry Vyukov <[hidden email]>
Reviewed-by: Darren Kenny <[hidden email]>
Reviewed-by: Marc Zyngier <[hidden email]>
Tested-by: Marc Zyngier <[hidden email]>
Cc: Paolo Bonzini <[hidden email]>
Cc: Radim Krčmář <[hidden email]>
Cc: Marc Zyngier <[hidden email]>
Cc: Christoffer Dall <[hidden email]>
Signed-off-by: Wanpeng Li <[hidden email]>
Signed-off-by: Paolo Bonzini <[hidden email]>
Signed-off-by: Khalid Elmously <[hidden email]>


---
 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 f7217fe16f87..f031c427713a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4140,7 +4140,7 @@ 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;
@@ -4388,7 +4388,7 @@ 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;
  }
@@ -4410,14 +4410,14 @@ 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",
--
2.14.1


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