From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752619AbbC2JCn (ORCPT ); Sun, 29 Mar 2015 05:02:43 -0400 Received: from mail-wg0-f49.google.com ([74.125.82.49]:36131 "EHLO mail-wg0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751001AbbC2JCj (ORCPT ); Sun, 29 Mar 2015 05:02:39 -0400 Date: Sun, 29 Mar 2015 11:02:34 +0200 From: Ingo Molnar To: Denys Vlasenko Cc: Andy Lutomirski , "H. Peter Anvin" , Brad Spengler , Linus Torvalds , Borislav Petkov , "linux-kernel@vger.kernel.org" , Thomas Gleixner , Andrew Lutomirski , "linux-tip-commits@vger.kernel.org" Subject: [PATCH] x86/asm/entry: Remove user_mode_ignore_vm86() Message-ID: <20150329090233.GA1963@gmail.com> References: <202c56ca63823c338af8e2e54948dbe222da6343.1426728647.git.luto@kernel.org> <20150324194402.GA27598@gmail.com> <55155F9E.3030605@redhat.com> <20150329070816.GD18007@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150329070816.GD18007@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Ingo Molnar wrote: > So what the function name wanted to express is something like this: > > if (user_mode_vm86_mode_already_checked_so_this_is_marginally_faster_but_dont_use_it_otherwise_because_that_would_be_a_roothole()) > { > ... > } > > but that name was considered somewhat long. So how about doing the patch below? Thanks, Ingo ===================================> >>From 6677d6f073cfda7f1036eb06d13faaad5c6742cc Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Sun, 29 Mar 2015 09:10:08 +0200 Subject: [PATCH] x86/asm/entry: Remove user_mode_ignore_vm86() user_mode_ignore_vm86() can be used instead of user_mode(), in places where we have already done a v8086_mode() security check of ptregs. But doing this check in the wrong place would be a bug that could result in security problems, and also the naming still isn't very clear. Furthermore, it only affects 32-bit kernels, while most development happens on 64-bit kernels. If we replace them with user_mode() checks then the cost is only a very minor increase in various slowpaths: text data bss dec hex filename 10573391 703562 1753042 13029995 c6d26b vmlinux.o.before 10573423 703562 1753042 13030027 c6d28b vmlinux.o.after So lets get rid of this distinction once and for all. Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Signed-off-by: Ingo Molnar --- arch/x86/include/asm/ptrace.h | 17 ----------------- arch/x86/kernel/cpu/perf_event.c | 2 +- arch/x86/kernel/traps.c | 6 +++--- 3 files changed, 4 insertions(+), 21 deletions(-) diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h index d20bae298852..19507ffa5d28 100644 --- a/arch/x86/include/asm/ptrace.h +++ b/arch/x86/include/asm/ptrace.h @@ -113,23 +113,6 @@ static inline int user_mode(struct pt_regs *regs) #endif } -/* - * This is the fastest way to check whether regs come from user space. - * It is unsafe if regs might come from vm86 mode, though -- in vm86 - * mode, all bits of CS and SS are completely under the user's control. - * The CPU considers vm86 mode to be CPL 3 regardless of CS and SS. - * - * Do NOT use this function unless you have already ruled out the - * possibility that regs came from vm86 mode. - * - * We check for RPL != 0 instead of RPL == 3 because we don't use rings - * 1 or 2 and this is more efficient. - */ -static inline int user_mode_ignore_vm86(struct pt_regs *regs) -{ - return (regs->cs & SEGMENT_RPL_MASK) != 0; -} - static inline int v8086_mode(struct pt_regs *regs) { #ifdef CONFIG_X86_32 diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c index 56f7e60ad732..e2888a3ad1e3 100644 --- a/arch/x86/kernel/cpu/perf_event.c +++ b/arch/x86/kernel/cpu/perf_event.c @@ -2159,7 +2159,7 @@ static unsigned long code_segment_base(struct pt_regs *regs) if (regs->flags & X86_VM_MASK) return 0x10 * regs->cs; - if (user_mode_ignore_vm86(regs) && regs->cs != __USER_CS) + if (user_mode(regs) && regs->cs != __USER_CS) return get_segment_base(regs->cs); #else if (user_mode(regs) && !user_64bit_mode(regs) && diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index c8eb469a94a4..6751c5c58eec 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -207,7 +207,7 @@ do_trap_no_signal(struct task_struct *tsk, int trapnr, char *str, return -1; } - if (!user_mode_ignore_vm86(regs)) { + if (!user_mode(regs)) { if (!fixup_exception(regs)) { tsk->thread.error_code = error_code; tsk->thread.trap_nr = trapnr; @@ -468,7 +468,7 @@ do_general_protection(struct pt_regs *regs, long error_code) } tsk = current; - if (!user_mode_ignore_vm86(regs)) { + if (!user_mode(regs)) { if (fixup_exception(regs)) goto exit; @@ -685,7 +685,7 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code) * We already checked v86 mode above, so we can check for kernel mode * by just checking the CPL of CS. */ - if ((dr6 & DR_STEP) && !user_mode_ignore_vm86(regs)) { + if ((dr6 & DR_STEP) && !user_mode(regs)) { tsk->thread.debugreg6 &= ~DR_STEP; set_tsk_thread_flag(tsk, TIF_SINGLESTEP); regs->flags &= ~X86_EFLAGS_TF;