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

Message ID 83bb6256fa9c13b95fc06635f7db66ed9388e027.1515046972.git.khalid.elmously@canonical.com
State New
Headers show
Series
  • CVE-2017-17741
Related show

Commit Message

Khalid Elmously Jan. 4, 2018, 6:58 a.m.
From: Wanpeng Li <wanpeng.li@hotmail.com>

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 <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>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.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(-)

Comments

Stefan Bader Jan. 23, 2018, 2:22 p.m. | #1
On 04.01.2018 07:58, Khalid Elmously wrote:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
> 
> 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 <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>
> Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>

> 
> 
> ---
Reminder to fix up backport line.

>  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",
>
Khalid Elmously Feb. 3, 2018, 1:37 a.m. | #2
Applied to Xenial

On 2018-01-04 01:58:25 , Khalid Elmously wrote:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
> 
> 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 <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>
> Signed-off-by: Khalid Elmously <khalid.elmously@canonical.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 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
>

Patch

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",