| From 7ce5a2b9bb2e92902230e3121d8c3047fab9cb47 Mon Sep 17 00:00:00 2001 |
| From: H. Peter Anvin <hpa@zytor.com> |
| Date: Fri, 23 Apr 2010 16:17:40 -0700 |
| Subject: x86-64: Clear a 64-bit FS/GS base on fork if selector is nonzero |
| |
| From: H. Peter Anvin <hpa@zytor.com> |
| |
| commit 7ce5a2b9bb2e92902230e3121d8c3047fab9cb47 upstream. |
| |
| When we do a thread switch, we clear the outgoing FS/GS base if the |
| corresponding selector is nonzero. This is taken by __switch_to() as |
| an entry invariant; it does not verify that it is true on entry. |
| However, copy_thread() doesn't enforce this constraint, which can |
| result in inconsistent results after fork(). |
| |
| Make copy_thread() match the behavior of __switch_to(). |
| |
| Reported-and-tested-by: Samuel Thibault <samuel.thibault@inria.fr> |
| Signed-off-by: H. Peter Anvin <hpa@zytor.com> |
| LKML-Reference: <4BD1E061.8030605@zytor.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
| |
| --- |
| arch/x86/kernel/process_64.c | 4 ++-- |
| 1 file changed, 2 insertions(+), 2 deletions(-) |
| |
| --- a/arch/x86/kernel/process_64.c |
| +++ b/arch/x86/kernel/process_64.c |
| @@ -282,12 +282,12 @@ int copy_thread(unsigned long clone_flag |
| |
| set_tsk_thread_flag(p, TIF_FORK); |
| |
| - p->thread.fs = me->thread.fs; |
| - p->thread.gs = me->thread.gs; |
| p->thread.io_bitmap_ptr = NULL; |
| |
| savesegment(gs, p->thread.gsindex); |
| + p->thread.gs = p->thread.gsindex ? 0 : me->thread.gs; |
| savesegment(fs, p->thread.fsindex); |
| + p->thread.fs = p->thread.fsindex ? 0 : me->thread.fs; |
| savesegment(es, p->thread.es); |
| savesegment(ds, p->thread.ds); |
| |
