[PATCH] arm/arm64: KVM: Feed initialized memory to MMIO accesses

[PATCH] arm/arm64: KVM: Feed initialized memory to MMIO accesses

[Marc Zyngier]

On an MMIO access, we always copy the on-stack buffer info
the shared "run" structure, even if this is a read access.
This ends up leaking up to 8 bytes of uninitialized memory
into userspace.

An obvious fix for this one is to only perform the copy if
this is an actual write.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/kvm/mmio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kvm/mmio.c b/arch/arm/kvm/mmio.c
index 7f33b20..0f6600f 100644
--- a/arch/arm/kvm/mmio.c
+++ b/arch/arm/kvm/mmio.c
@@ -206,7 +206,8 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	run->mmio.is_write	= is_write;
 	run->mmio.phys_addr	= fault_ipa;
 	run->mmio.len		= len;
-	memcpy(run->mmio.data, data_buf, len);
+	if (is_write)
+		memcpy(run->mmio.data, data_buf, len);
 
 	if (!ret) {
 		/* We handled the access successfully in the kernel. */
-- 
2.1.4

Re: [PATCH] arm/arm64: KVM: Feed initialized memory to MMIO accesses

[Christoffer Dall]

On Wed, Feb 17, 2016 at 03:34:20PM +0000, Marc Zyngier wrote:
> On an MMIO access, we always copy the on-stack buffer info
> the shared "run" structure, even if this is a read access.
> This ends up leaking up to 8 bytes of uninitialized memory
> into userspace.

I think it only leaks 'len' bytes to userspace ;)

> 
> An obvious fix for this one is to only perform the copy if
> this is an actual write.

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>

> 
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm/kvm/mmio.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/kvm/mmio.c b/arch/arm/kvm/mmio.c
> index 7f33b20..0f6600f 100644
> --- a/arch/arm/kvm/mmio.c
> +++ b/arch/arm/kvm/mmio.c
> @@ -206,7 +206,8 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
>  	run->mmio.is_write	= is_write;
>  	run->mmio.phys_addr	= fault_ipa;
>  	run->mmio.len		= len;
> -	memcpy(run->mmio.data, data_buf, len);
> +	if (is_write)
> +		memcpy(run->mmio.data, data_buf, len);
>  
>  	if (!ret) {
>  		/* We handled the access successfully in the kernel. */
> -- 
> 2.1.4
> 

Re: [PATCH] arm/arm64: KVM: Feed initialized memory to MMIO accesses

[Marc Zyngier]

On 24/02/16 11:40, Christoffer Dall wrote:
> On Wed, Feb 17, 2016 at 03:34:20PM +0000, Marc Zyngier wrote:
>> On an MMIO access, we always copy the on-stack buffer info
>> the shared "run" structure, even if this is a read access.
>> This ends up leaking up to 8 bytes of uninitialized memory
>> into userspace.
> 
> I think it only leaks 'len' bytes to userspace ;)
> 
>>
>> An obvious fix for this one is to only perform the copy if
>> this is an actual write.
> 
> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>

Thanks. I've pushed this onto master, with a view of sending a PR to
Paolo this evening (hopefully the last one for this cycle).

	M.
-- 
Jazz is not dead. It just smells funny...