[PATCH] loader: Check if the preloader overlaps the reserved range on the Mac.

[Ken Thomases]

On Dec 6, 2018, at 10:20 AM, Sebastian Lackner <sebastian at fds-team.de> wrote:
> 
> Am Do., 6. Dez. 2018 um 17:09 Uhr schrieb Ken Thomases <ken at codeweavers.com>:
>> 
>> Hi Sebastian,
>> 
>> On Dec 6, 2018, at 9:53 AM, Sebastian Lackner <sebastian at fds-team.de> wrote:
>>> 
>>> Am Mi., 5. Dez. 2018 um 23:22 Uhr schrieb Ken Thomases <ken at codeweavers.com>:
>>>> @@ -562,6 +598,11 @@ void *wld_start( void *stack, int *is_unix_thread )
>>>>        p++;
>>>>    }
>>>> 
>>>> +    LOAD_POSIX_DYLD_FUNC( dlopen );
>>>> +    LOAD_POSIX_DYLD_FUNC( dlsym );
>>>> +    LOAD_POSIX_DYLD_FUNC( dladdr );
>>>> +    LOAD_MACHO_DYLD_FUNC( _dyld_get_image_slide );
>>>> +
>>>>    /* reserve memory that Wine needs */
>>>>    if (reserve) preload_reserve( reserve );
>>>>    for (i = 0; preload_info[i].size; i++)
>>>> @@ -576,11 +617,6 @@ void *wld_start( void *stack, int *is_unix_thread )
>>>>    if (!map_region( &builtin_dlls ))
>>>>        builtin_dlls.size = 0;
>>>> 
>>>> -    LOAD_POSIX_DYLD_FUNC( dlopen );
>>>> -    LOAD_POSIX_DYLD_FUNC( dlsym );
>>>> -    LOAD_POSIX_DYLD_FUNC( dladdr );
>>>> -    LOAD_MACHO_DYLD_FUNC( _dyld_get_image_slide );
>>>> -
>>>>    /* load the main binary */
>>>>    if (!(mod = pdlopen( argv[1], RTLD_NOW )))
>>>>        fatal_error( "%s: could not load binary\n", argv[1] );
>>> 
>>> I am not sure anymore if the system libs (dlopen, etc.) are already
>>> loaded by the kernel, or if they are loaded on the first
>>> _dyld_func_lookup() call. Could you maybe check that? In the second
>>> case, changing the order means that there is a higher risk of running
>>> into some address space conflicts.
>> 
>> Thanks for reviewing!
>> 
>> I considered the question of whether looking up the functions earlier might load additional images, but it shouldn't.  Those functions don't come from libSystem, they come from dyld itself (which is, of course, already loaded).
>> 
>> I just confirmed by forcing a crash just before dlopen-ing the main executable and looking at the macOS crash report.  It shows the loaded images and it's just wine-preloader and dyld.
>> 
>> -Ken
>> 
> 
> Hello Ken,
> 
> since it seems pretty easy to check, I would also recommend to verify
> that dyld is indeed already loaded before calling any of the lookup
> functions. We only link against a small *.o file, so in theory, the
> kernel could still use lazy-loading for the dylib. If this shows that
> dyld is already loaded, then it indeed doesn't make any difference.

Dyld is definitely loaded before our code is run.  The kernel loads the executable (but not its dependencies) and dyld and then starts the process in dyld, giving it a pointer to where the executable is.  Without dyld already loaded, there'd be no way to load it or anything else (even lazy-loaded symbols).  It's the loader, the thing that loads. ;)

But, just to confirm, I forced the crash at the very beginning of wld_start() and dyld is loaded.

> BTW: Thanks for your effort to get this upstream.

Happy to do it.  And thank you and Michael for the original work.

-Ken