Re: [RFC PATCH] linux-user/mmap: Return EFAULT for invalid addresses

[Richard Purdie]

On Fri, 2021-01-08 at 17:46 +0000, Richard Purdie wrote:
> When using qemu-i386 to run gobject introspection parts of a webkitgtk 
> build using musl as libc on a 64 bit host, it sits in an infinite loop 
> of mremap calls of ever decreasing/increasing addresses.
> 
> I suspect something in the musl memory allocation code loops indefinitely
> if it only sees ENOMEM and only exits when it hits EFAULT.
> 
> According to the docs, trying to mremap outside the address space
> can/should return EFAULT and changing this allows the build to succeed.
> 
> There was previous discussion of this as it used to work before qemu 2.11
> and we've carried hacks to work around it since, this appears to be a
> better fix of the real issue?
> 
> 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 +727,7 @@ abi_long target_mremap(abi_ulong old_add
>           !guest_range_valid(new_addr, new_size)) ||
>          ((flags & MREMAP_MAYMOVE) == 0 &&
>           !guest_range_valid(old_addr, new_size))) {
> -        errno = ENOMEM;
> +        errno = EFAULT;
>          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