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

[Philippe Mathieu-Daudé]

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

You forgot to Cc the maintainer who likely missed it due to the huge
traffic:

$ ./scripts/get_maintainer.pl -f linux-user/mmap.c
Laurent Vivier <laurent@vivier.eu> (maintainer:Linux user)

Now Cc'ed.

Regards,

Phil.