Andy Lutomirski 3669ef9fa7 x86, tls: Interpret an all-zero struct user_desc as "no segment" ... The Witcher 2 did something like this to allocate a TLS segment index: struct user_desc u_info; bzero(&u_info, sizeof(u_info)); u_info.entry_number = (uint32_t)-1; syscall(SYS_set_thread_area, &u_info); Strictly speaking, this code was never correct. It should have set read_exec_only and seg_not_present to 1 to indicate that it wanted to find a free slot without putting anything there, or it should have put something sensible in the TLS slot if it wanted to allocate a TLS entry for real. The actual effect of this code was to allocate a bogus segment that could be used to exploit espfix. The set_thread_area hardening patches changed the behavior, causing set_thread_area to return -EINVAL and crashing the game. This changes set_thread_area to interpret this as a request to find a free slot and to leave it empty, which isn't *quite* what the game expects but should be close enough to keep it working. In particular, using the code above to allocate two segments will allocate the same segment both times. According to FrostbittenKing on Github, this fixes The Witcher 2. If this somehow still causes problems, we could instead allocate a limit==0 32-bit data segment, but that seems rather ugly to me. Fixes: 41bdc78544 x86/tls: Validate TLS entries to protect espfix Signed-off-by: Andy Lutomirski <luto@amacapital.net> Cc: stable@vger.kernel.org Cc: torvalds@linux-foundation.org Link: http://lkml.kernel.org/r/0cb251abe1ff0958b8e468a9a9a905b80ae3a746.1421954363.git.luto@amacapital.net Signed-off-by: Thomas Gleixner <tglx@linutronix.de>		2015-01-22 21:45:07 +01:00
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asm	x86, tls: Interpret an all-zero struct user_desc as "no segment"	2015-01-22 21:45:07 +01:00
uapi/asm