Re: [PATCH 2/4] linux-user: fix mremap errors for invalid ranges

[Richard Henderson <richard.henderson@linaro.org>]

On 10/11/25 15:03, Matthew Lugg wrote:
> If an address range given to `mremap` is invalid (exceeds addressing
> bounds on the guest), we were previously returning `ENOMEM`, which is
> not correct. The manpage and the Linux kernel implementation both agree
> that if `old_addr`/`old_size` refer to an invalid address, `EFAULT` is
> returned, and if `new_addr`/`new_size` refer to an invalid address,
> `EINVAL` is returned.
> 
> Signed-off-by: Matthew Lugg <mlugg@mlugg.co.uk>
> ---
>   linux-user/mmap.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> index ec8392b35b..4c5fe832ad 100644
> --- a/linux-user/mmap.c
> +++ b/linux-user/mmap.c
> @@ -1103,12 +1103,15 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
>       int prot;
>       void *host_addr;
>   
> -    if (!guest_range_valid_untagged(old_addr, old_size) ||
> -        ((flags & MREMAP_FIXED) &&
> +    if (!guest_range_valid_untagged(old_addr, old_size)) {
> +        errno = EFAULT;
> +        return -1;
> +    }
> +    if (((flags & MREMAP_FIXED) &&
>            !guest_range_valid_untagged(new_addr, new_size)) ||
>           ((flags & MREMAP_MAYMOVE) == 0 &&
>            !guest_range_valid_untagged(old_addr, new_size))) {
> -        errno = ENOMEM;
> +        errno = EINVAL;
>           return -1;
>       }
>   

The order of the checks here is wrong.  We should match do_remap and check_mremap_params. 
In particular, it appears as if all of the EINVAL checks come first.


r~