Re: [PATCH] Fix i386 memmove issue [BZ #22644]

[Andrew Senkevich <andrew.n.senkevich@gmail.com>]

2018-03-19 14:17 GMT+01:00 Florian Weimer <fweimer@redhat.com>:
> On 03/19/2018 02:11 PM, Andreas Schwab wrote:
>>
>> On Mär 19 2018, Andrew Senkevich<andrew.n.senkevich@gmail.com>  wrote:
>>
>>> +static void
>>> +do_test2 (void)
>>> +{
>>> +  uint32_t num = 0x20000000;
>>> +  uint32_t * large_buf;
>>> +
>>> +  large_buf = mmap ((void*)0x70000000, num, PROT_READ | PROT_WRITE,
>>> +     MAP_PRIVATE | MAP_ANON | MAP_FIXED, -1, 0);
>>
>> Since you are using MAP_FIXED this may overwrite an existing mapping.
>
>
> Leading to a hard-to-debug crash, maybe sporadically due to ASLR.  Yes, I
> have this concern as well.
>
> There was a long, long Linux thread about a non-overriding MAP_FIXED
> variant, but as far as I can see, this has not been merged.  Maybe it would
> have helped here.
>
> Is it very difficult to split out this test into a separate test file? Then
> link the whole thing statically, as non-PIE, and keep using MAP_FIXED.  This
> should make it quite likely that you don't override anything valuable.

I think not very difficult, I will try this way.


--
WBR,
Andrew