Re: [PATCH] linux-user/mmap: Avoid asserts for out of range mremap calls

[Richard Purdie]

On Fri, 2021-01-08 at 17:42 +0000, Richard Purdie wrote:
> If mremap() is called without the MREMAP_MAYMOVE flag with a start address
> just before the end of memory (reserved_va) where new_size would exceed 
> it (and GUEST_ADDR_MAX), the assert(end - 1 <= GUEST_ADDR_MAX) in 
> page_set_flags() would trigger.
> 
> Add an extra guard to the guest_range_valid() checks to prevent this and
> avoid asserting binaries when reserved_va is set.
> 
> This meant a bug I was seeing locally now gives the same behaviour 
> regardless of whether reserved_va is set or not.
> 
> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org
> 
> Index: qemu-5.2.0/linux-user/mmap.c
> ===================================================================
> --- qemu-5.2.0.orig/linux-user/mmap.c
> +++ qemu-5.2.0/linux-user/mmap.c
> @@ -727,7 +727,9 @@ abi_long target_mremap(abi_ulong old_add
>  
> 
>      if (!guest_range_valid(old_addr, old_size) ||
>          ((flags & MREMAP_FIXED) &&
> -         !guest_range_valid(new_addr, new_size))) {
> +         !guest_range_valid(new_addr, new_size)) ||
> +        ((flags & MREMAP_MAYMOVE) == 0 &&
> +         !guest_range_valid(old_addr, new_size))) {
>          errno = ENOMEM;
>          return -1;
>      }
> 
> 

Any comments on this? I believe its a valid issue that needs fixing and
multiple distros appear to be carrying fixes in this area related to
this.

Cheers,

Richard