[PATCH] KVM: arm64: Fix buffer overflow in kvm_arm_set_fw_reg()

[Dan Carpenter]

On Wed, Apr 19, 2023 at 09:48:41AM +0100, Steven Price wrote:
> On 19/04/2023 09:06, Dan Carpenter wrote:
> > The KVM_REG_SIZE() comes from the ioctl and it can be a power of two
> > between 0-32768 but if it is more than sizeof(long) this will corrupt
> > memory.
> > 
> > Fixes: 99adb567632b ("KVM: arm/arm64: Add save/restore support for firmware workaround state")
> > Signed-off-by: Dan Carpenter <dan.carpenter at linaro.org>
> 
> Reviewed-by: Steven Price <steven.price at arm.com>
> 
> Although there might be something to be said for rejecting anything
> where KVM_REG_SIZE(reg->id) != sizeof(u64), as for smaller sizes the top
> bits of val would be undefined which would require the code to mask the
> top bits out to be safe. Given that all registers are currently u64 (and
> I don't expect that to change), perhaps the below would be clearer?
> 
> 	if (KVM_REG_SIZE(reg->id) != sizeof(val))
> 		return -EINVAL;
> 	if (copy_from_user(&val, uaddr, sizeof(val)))
> 		return -EFAULT;

I was thinking that zero might be a valid size?

regards,
dan carpenter