[PATCH] Support for game DRM which overwrite the GS segment selector

Alessandro Pignotti alexpigna.dev at gmail.com
Wed Jan 30 10:12:46 CST 2013

Hi again,

I've quickly implemented the aforementioned idea of fixing the segment
in the segfault handler when needed. I'm attaching my proposed patch.


Il giorno mer, 30/01/2013 alle 16.44 +0100, Alessandro Pignotti ha
> Hi everyone,
> I'm trying to get a specific game which employs a seemingly custom
> protection scheme to work. The DRM does various bad things as usual, but
> a very bad one is manipulating to GS segment selector and setting it to
> a NULL segment. The GS segment is used by libc though in various ways
> (stack protection and syscall support, and probably others).
> I managed to get the activation procedure to go further and further by
> enclosing each offending syscall using the following 2 macros.
> #define SAFE_GS_START \
>     do { \
>         wine_set_gs(ntdll_get_thread_data()->gs); \
>         do
> #define SAFE_GS_END \
>         while(0); \
>     } while(0)
> Still, this method is very cumbersome since system calls happens in many
> places even outside of ntdll. Fixing the GS is also needed to support
> sigsetjmp which is used by wine's exception handling.
> I'd like to ask for feedback about what would be a sane way of
> supporting this application. A possible solution would be to modify
> wine's segfault handler to check if the instruction has a GS prefix
> (0x65 IIRC) and try to execute the instruction again after fixing the
> GS.
> Please keep me in CC since I'm not subscribed to the ML.
> Regards,
> Alessandro Pignotti

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