x86/arch_prctl: Fix ARCH_GET_FS and ARCH_GET_GS
authorAndy Lutomirski <luto@kernel.org>
Fri, 8 Apr 2016 00:31:45 +0000 (17:31 -0700)
committerIngo Molnar <mingo@kernel.org>
Wed, 13 Apr 2016 08:20:41 +0000 (10:20 +0200)
commitd47b50e7a111bb7a56fb1c974728b56209d7f515
tree1c3edd2d20f4901b14e2988ecb0c404ff6e54541
parent0051202f6ad5fd9c04d220343e66d1eb890f7b81
x86/arch_prctl: Fix ARCH_GET_FS and ARCH_GET_GS

ARCH_GET_FS and ARCH_GET_GS attempted to figure out the fsbase and
gsbase respectively from saved thread state.  This was wrong: fsbase
and gsbase live in registers while a thread is running, not in
memory.

For reasons I can't fathom, the fsbase and gsbase code were
different.  Since neither was correct, I didn't try to figure out
what the point of the difference was.

Change it to simply read the MSRs.

The code for reading the base for a remote thread is also completely
wrong if the target thread uses its own descriptors (which is the case
for all 32-bit threaded programs), but fixing that is a different
story.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rudolf Marek <r.marek@assembler.cz>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/c6e7b507c72ca3bdbf6c7a8a3ceaa0334e873bd9.1460075211.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
arch/x86/kernel/process_64.c