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From: Andy Lutomirski <luto@amacapital.net>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Brian Gerst <brgerst@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Denys Vlasenko <vda.linux@googlemail.com>,
	Andrew Lutomirski <luto@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	Rik van Riel <riel@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Borislav Petkov <bp@alien8.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Oleg Nesterov <oleg@redhat.com>,
	Kees Cook <keescook@chromium.org>,
	"linux-tip-commits@vger.kernel.org" 
	<linux-tip-commits@vger.kernel.org>
Subject: Re: [tip:x86/asm] x86/entry: Add enter_from_user_mode() and use it in syscalls
Date: Tue, 14 Jul 2015 16:04:47 -0700
Message-ID: <CALCETrUGCsRWJrkMX0pAq_twfGbcsNrAZBMcF8n_eOXGt0c_ew@mail.gmail.com> (raw)
In-Reply-To: <20150714230057.GC29441@lerouge>

On Tue, Jul 14, 2015 at 4:00 PM, Frederic Weisbecker <fweisbec@gmail.com> wrote:
> On Tue, Jul 07, 2015 at 03:51:29AM -0700, tip-bot for Andy Lutomirski wrote:
>> Commit-ID:  feed36cde0a10adb957445a37e48f957f30b2273
>> Gitweb:     http://git.kernel.org/tip/feed36cde0a10adb957445a37e48f957f30b2273
>> Author:     Andy Lutomirski <luto@kernel.org>
>> AuthorDate: Fri, 3 Jul 2015 12:44:25 -0700
>> Committer:  Ingo Molnar <mingo@kernel.org>
>> CommitDate: Tue, 7 Jul 2015 10:59:06 +0200
>>
>> x86/entry: Add enter_from_user_mode() and use it in syscalls
>>
>> 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 <luto@kernel.org>
>> 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: Denys Vlasenko <vda.linux@googlemail.com>
>> Cc: Frederic Weisbecker <fweisbec@gmail.com>
>> Cc: H. Peter Anvin <hpa@zytor.com>
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: Linus Torvalds <torvalds@linux-foundation.org>
>> Cc: Oleg Nesterov <oleg@redhat.com>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Rik van Riel <riel@redhat.com>
>> Cc: Thomas Gleixner <tglx@linutronix.de>
>> Cc: paulmck@linux.vnet.ibm.com
>> Link: http://lkml.kernel.org/r/853b42420066ec3fb856779cdc223a6dcb5d355b.1435952415.git.luto@kernel.org
>> Signed-off-by: Ingo Molnar <mingo@kernel.org>
>> ---
>>  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 917d0c3..9a327ee 100644
>> --- a/arch/x86/entry/common.c
>> +++ b/arch/x86/entry/common.c
>> @@ -28,6 +28,15 @@
>>  #define CREATE_TRACE_POINTS
>>  #include <trace/events/syscalls.h>
>>
>> +#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;
>
> We should move the sanity check to user_exit/enter() and use user_exit/enter()
> only when we actually enter/exit user.

I agree, but I don't know what other arches to.

> Here it's the case but syscall_trace_leave()
> and do_notify_resume() are special case that should probably use exception_enter/exit()
> unless your patchset have changed things such that there is only one call to user_exit()
> once we completed everything before resuming userspace. I need to review the rest of
> the patchset to discover that :-)

syscall_trace_leave and do_notify_resume may be so screwed up that
your suggestion wouldn't even work.  However, the next set of patches
(out for review but currently stalled pending Brian Gerst's vm86 work)
remove those functions entirely.

--Andy

  reply index

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-07-03 19:44 [PATCH v5 00/17] x86: Rewrite exit-to-userspace code Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 01/17] selftests/x86: Add a test for 32-bit fast syscall arg faults Andy Lutomirski
2015-07-07 10:49   ` [tip:x86/asm] x86/entry, " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 02/17] x86/entry/64/compat: Fix bad fast syscall arg failure path Andy Lutomirski
2015-07-07 10:49   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 03/17] uml: Fix do_signal() prototype Andy Lutomirski
2015-07-07 10:49   ` [tip:x86/asm] um: " tip-bot for Ingo Molnar
2015-07-03 19:44 ` [PATCH v5 04/17] context_tracking: Add ct_state and CT_WARN_ON Andy Lutomirski
2015-07-07 10:50   ` [tip:x86/asm] context_tracking: Add ct_state() and CT_WARN_ON() tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 05/17] notifiers: Assert that RCU is watching in notify_die Andy Lutomirski
2015-07-07 10:50   ` [tip:x86/asm] notifiers, RCU: Assert that RCU is watching in notify_die() tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 06/17] x86: Move C entry and exit code to arch/x86/entry/common.c Andy Lutomirski
2015-07-07 10:50   ` [tip:x86/asm] x86/entry: Move C entry and exit code to arch/x86/ entry/common.c tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 07/17] x86/traps: Assert that we're in CONTEXT_KERNEL in exception entries Andy Lutomirski
2015-07-07 10:51   ` [tip:x86/asm] x86/traps, context_tracking: Assert that we' re " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 08/17] x86/entry: Add enter_from_user_mode and use it in syscalls Andy Lutomirski
2015-07-07 10:51   ` [tip:x86/asm] x86/entry: Add enter_from_user_mode() " tip-bot for Andy Lutomirski
2015-07-14 23:00     ` Frederic Weisbecker
2015-07-14 23:04       ` Andy Lutomirski [this message]
2015-07-14 23:28         ` Frederic Weisbecker
2015-12-21 20:50   ` [PATCH v5 08/17] x86/entry: Add enter_from_user_mode " Sasha Levin
2015-12-21 22:44     ` Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 09/17] x86/entry: Add new, comprehensible entry and exit hooks Andy Lutomirski
2015-07-07 10:51   ` [tip:x86/asm] x86/entry: Add new, comprehensible entry and exit handlers written in C tip-bot for Andy Lutomirski
2015-07-14 23:07     ` Frederic Weisbecker
2015-07-15 19:56       ` Linus Torvalds
2015-07-15 20:46         ` Andy Lutomirski
2015-07-15 21:25           ` [PATCH] x86/entry: Fix _TIF_USER_RETURN_NOTIFY check in prepare_exit_to_usermode Andy Lutomirski
2015-07-18  3:25             ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 10/17] x86/entry/64: Really create an error-entry-from-usermode code path Andy Lutomirski
2015-07-07 10:52   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 11/17] x86/entry/64: Migrate 64-bit and compat syscalls to new exit hooks Andy Lutomirski
2015-07-07 10:52   ` [tip:x86/asm] x86/entry/64: Migrate 64-bit and compat syscalls to the new exit handlers and remove old assembly code tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 12/17] x86/asm/entry/64: Save all regs on interrupt entry Andy Lutomirski
2015-07-07 10:52   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 13/17] x86/asm/entry/64: Simplify irq stack pt_regs handling Andy Lutomirski
2015-07-07 10:53   ` [tip:x86/asm] x86/asm/entry/64: Simplify IRQ " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 14/17] x86/asm/entry/64: Migrate error and interrupt exit work to C Andy Lutomirski
2015-07-07 10:53   ` [tip:x86/asm] x86/asm/entry/64: Migrate error and IRQ exit work to C and remove old assembly code tip-bot for Andy Lutomirski
2015-08-11 22:18     ` Frederic Weisbecker
2015-08-11 22:25       ` Andy Lutomirski
2015-08-11 22:49         ` Frederic Weisbecker
2015-08-11 22:59           ` Andy Lutomirski
2015-08-12  1:02             ` Paul E. McKenney
2015-08-12 13:13             ` Frederic Weisbecker
2015-08-11 22:38     ` Frederic Weisbecker
2015-08-11 22:51       ` Andy Lutomirski
2015-08-11 23:22         ` Frederic Weisbecker
2015-08-11 23:33           ` Andy Lutomirski
2015-08-12 13:32             ` Frederic Weisbecker
2015-08-12 14:59               ` Andy Lutomirski
2015-08-18 22:34                 ` Frederic Weisbecker
2015-08-18 22:40                   ` Andy Lutomirski
2015-08-19 17:18                     ` Frederic Weisbecker
2015-08-19 18:02                       ` Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 15/17] x86/entry: Remove exception_enter from most trap handlers Andy Lutomirski
2015-07-07 10:53   ` [tip:x86/asm] x86/entry: Remove exception_enter() " tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 16/17] x86/entry: Remove SCHEDULE_USER and asm/context-tracking.h Andy Lutomirski
2015-07-07 10:54   ` [tip:x86/asm] x86/entry: Remove SCHEDULE_USER and asm/ context-tracking.h tip-bot for Andy Lutomirski
2015-07-03 19:44 ` [PATCH v5 17/17] x86/irq: Document how IRQ context tracking works and add an assertion Andy Lutomirski
2015-07-07 10:54   ` [tip:x86/asm] x86/irq, context_tracking: Document how IRQ context tracking works and add an RCU assertion tip-bot for Andy Lutomirski
2015-07-14 23:26     ` Frederic Weisbecker
2015-07-14 23:33       ` Andy Lutomirski
2015-07-18 13:23         ` Frederic Weisbecker
2015-07-18 14:10           ` Paul E. McKenney
2015-07-07 11:12 ` [PATCH v5 00/17] x86: Rewrite exit-to-userspace code Ingo Molnar
2015-07-07 16:03   ` Andy Lutomirski
2015-07-07 17:55     ` [PATCH] x86/entry/64: Fix warning on compat syscalls with CONFIG_AUDITSYSCALL=n Andy Lutomirski
2015-07-08  9:57       ` [tip:x86/asm] x86/entry/64: Fix IRQ state confusion and related warning on compat syscalls with CONFIG_AUDITSYSCALL =n tip-bot for Andy Lutomirski
2015-07-08 19:12       ` tip-bot for Andy Lutomirski

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