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

Christoffer Dall
2016-02-24T11:39:46Z

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
>