Path: csiph.com!aioe.org!newsfeed.CARNet.hr!news.spin.it!bofh.it!news.nic.it!robomod From: Andy Lutomirski Newsgroups: linux.kernel Subject: [PATCH v3 06/15] x86/entry: Add enter_from_user_mode and use it in syscalls Date: Wed, 24 Jun 2015 04:50:01 +0200 Message-ID: References: X-Original-To: x86@kernel.org, linux-kernel@vger.kernel.org X-Mailer: git-send-email 2.4.3 Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 68 Organization: linux.* mail to news gateway X-Original-Cc: =?UTF-8?q?Fr=C3=A9d=C3=A9ric=20Weisbecker?= , Rik van Riel , Oleg Nesterov , Denys Vlasenko , Borislav Petkov , Kees Cook , Brian Gerst , paulmck@linux.vnet.ibm.com, Andy Lutomirski X-Original-Date: Tue, 23 Jun 2015 19:46:09 -0700 X-Original-Message-ID: <3610838cd3716f4c839387f51c9bed8a7e7550d7.1435113808.git.luto@kernel.org> X-Original-References: X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: aioe.org linux.kernel:1171034 Changing the x86 context tracking hooks is dangerous because there are no good checks that we track our context correctly. Add a helper to check that we're actually in CONTEXT_USER when we enter from user mode and wire it up for syscall entries. Subsequent patches will wire this up for all non-NMI entries as well. NMIs are their own special beast and cannot currently switch overall context tracking state. Instead, they have their own special RCU hooks. This is a tiny speedup if !CONFIG_CONTEXT_TRACKING (removes a branch) and a tiny slowdown if CONFIG_CONTEXT_TRACING (adds a layer of indirection). Eventually, we should fix up the core context tracking code to supply a function that does what we want (and can be much simpler than user_exit), which will enable us to get rid of the extra call. Signed-off-by: Andy Lutomirski --- arch/x86/entry/common.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 348465473e55..8a7e35af7164 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -28,6 +28,15 @@ #define CREATE_TRACE_POINTS #include +#ifdef CONFIG_CONTEXT_TRACKING +/* Called on entry from user mode with IRQs off. */ +__visible void enter_from_user_mode(void) +{ + CT_WARN_ON(ct_state() != CONTEXT_USER); + user_exit(); +} +#endif + static void do_audit_syscall_entry(struct pt_regs *regs, u32 arch) { #ifdef CONFIG_X86_64 @@ -65,14 +74,16 @@ unsigned long syscall_trace_enter_phase1(struct pt_regs *regs, u32 arch) work = ACCESS_ONCE(current_thread_info()->flags) & _TIF_WORK_SYSCALL_ENTRY; +#ifdef CONFIG_CONTEXT_TRACKING /* * If TIF_NOHZ is set, we are required to call user_exit() before * doing anything that could touch RCU. */ if (work & _TIF_NOHZ) { - user_exit(); + enter_from_user_mode(); work &= ~_TIF_NOHZ; } +#endif #ifdef CONFIG_SECCOMP /* -- 2.4.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/