Re: [PATCH v1 14/14] linux-user: detect overflow of MAP_FIXED mmap

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 6/5/20 5:49 PM, Alex Bennée wrote:
> Relaxing the restrictions on 64 bit guests leads to the user being
> able to attempt to map right at the edge of addressable memory. This
> in turn lead to address overflow tripping the assert in page_set_flags
> when the end address wrapped around.
> 
> Detect the wrap earlier and correctly -ENOMEM the guest (in the
> reported case LTP mmap15).
> 
> Fixes: 7d8cbbabcb

Reported-by: Laurent Vivier <laurent@vivier.eu>

> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>  linux-user/mmap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> index e3780337974..2e05bd499e6 100644
> --- a/linux-user/mmap.c
> +++ b/linux-user/mmap.c
> @@ -467,7 +467,7 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int prot,
>           * It can fail only on 64-bit host with 32-bit target.
>           * On any other target/host host mmap() handles this error correctly.
>           */
> -        if (!guest_range_valid(start, len)) {
> +        if (end < start || !guest_range_valid(start, len)) {
>              errno = ENOMEM;
>              goto fail;
>          }
>