Re: [PATCH kvmtool 5/5] mmio: Sanitize addr and len

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi Martin,

On Tue, Jan 18, 2022 at 12:12:03AM +0200, Martin Radev wrote:
> This patch verifies that adding the addr and length arguments
> from an MMIO op do not overflow. This is necessary because the
> arguments are controlled by the VM. The length may be set to
> an arbitrary value by using the rep prefix.

The Arm architecture doesn'tt have instructions to access 0 bytes of
memory. By "rep prefix" you mean the x86 rep* instructions, right?

> 
> Signed-off-by: Martin Radev <martin.b.radev@gmail.com>
> ---
>  mmio.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/mmio.c b/mmio.c
> index a6dd3aa..04d2af6 100644
> --- a/mmio.c
> +++ b/mmio.c
> @@ -32,6 +32,10 @@ static struct mmio_mapping *mmio_search(struct rb_root *root, u64 addr, u64 len)
>  {
>  	struct rb_int_node *node;
>  
> +	/* If len is zero or if there's an overflow, the MMIO op is invalid. */
> +	if (len + addr <= addr)

Would you mind rewriting the left side of the inequality to addr + len to match
the argument to rb_int_search_range() below?

Otherwise looks good:

Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>

Thanks,
Alex

> +		return NULL;
> +
>  	node = rb_int_search_range(root, addr, addr + len);
>  	if (node == NULL)
>  		return NULL;
> -- 
> 2.25.1
>