Re: [PATCH v4 0/2] MR7064: ntdll: Check for invalid %gs value in 32-bit code on WoW64.

[Jinoh Kang (＠iamahuman)]

Jinoh Kang (@iamahuman) commented about dlls/ntdll/unix/signal_x86_64.c:
> -
>    __asm__ volatile ("rdgsbase %0" : "=r" (cur_gs));
> - else
> -
>    cur_gs = arch_prctl( ARCH_GET_GS, teb );
>
> +#elif defined(__FreeBSD__) || defined(__FreeBSD_kernel__)
> - amd64_get_gsbase( &cur_gs );
>
> +#elif defined(__NetBSD__)
> - sysarch( X86_64_GET_GSBASE, &cur_gs );
>
> +#elif defined(__APPLE__)
> - cur_gs = (ULONG_PTR)mac_thread_gsbase();
>
> +#else
> +# error Please define getting %gs for your architecture
> +#endif
> -
> - if ((WORD)cur_gs == system_gs) return FALSE;
> -
> - TRACE( "%04hx/%04hx at %p, fixing up\n", (WORD)cur_gs, system_gs, instr );

`signal_i386.c check_invalid_gs` had explicit check for GS: prefix. We should do something similar here.

See `is_privileged_instr` for a comprehensive list of prefixes on x86_64.