From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from wtarreau.pck.nerim.net ([62.212.114.60]:36227 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934700AbbEOIP5 (ORCPT ); Fri, 15 May 2015 04:15:57 -0400 Message-Id: <20150515080530.807107185@1wt.eu> Date: Fri, 15 May 2015 10:05:42 +0200 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Andy Lutomirski , Borislav Petkov , Denys Vlasenko , "H. Peter Anvin" , Linus Torvalds , Oleg Nesterov , Thomas Gleixner , Ingo Molnar , Ben Hutchings , Willy Tarreau Subject: [ 12/48] x86/asm/entry/64: Remove a bogus ret_from_fork optimization MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 In-Reply-To: <9c2783dfae10ef2d1e9b08bcc1e562c5@local> Sender: stable-owner@vger.kernel.org List-ID: 2.6.32-longterm review patch. If anyone has any objections, please let me know. ------------------ From: Andy Lutomirski commit 956421fbb74c3a6261903f3836c0740187cf038b upstream. 'ret_from_fork' checks TIF_IA32 to determine whether 'pt_regs' and the related state make sense for 'ret_from_sys_call'. This is entirely the wrong check. TS_COMPAT would make a little more sense, but there's really no point in keeping this optimization at all. This fixes a return to the wrong user CS if we came from int 0x80 in a 64-bit task. Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/4710be56d76ef994ddf59087aad98c000fbab9a4.1424989793.git.luto@amacapital.net [ Backported from tip:x86/asm. ] Signed-off-by: Ingo Molnar Signed-off-by: Ben Hutchings (cherry picked from commit 159891c0953a89a28f793fc52373b031262c44d2) Signed-off-by: Willy Tarreau --- arch/x86/kernel/entry_64.S | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index d9bcee0..303eaeb8 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -413,11 +413,14 @@ ENTRY(ret_from_fork) testl $3, CS-ARGOFFSET(%rsp) # from kernel_thread? je int_ret_from_sys_call - testl $_TIF_IA32, TI_flags(%rcx) # 32-bit compat task needs IRET - jnz int_ret_from_sys_call - - RESTORE_TOP_OF_STACK %rdi, -ARGOFFSET - jmp ret_from_sys_call # go to the SYSRET fastpath + /* + * By the time we get here, we have no idea whether our pt_regs, + * ti flags, and ti status came from the 64-bit SYSCALL fast path, + * the slow path, or one of the ia32entry paths. + * Use int_ret_from_sys_call to return, since it can safely handle + * all of the above. + */ + jmp int_ret_from_sys_call CFI_ENDPROC END(ret_from_fork) -- 1.7.12.2.21.g234cd45.dirty