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

[Philippe Mathieu-Daudé]

Cc'ing maintainer

On 1/22/21 10:37 AM, Richard Purdie wrote:
> 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
> 
>