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From: Brian Gerst <brgerst@gmail.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>,
	X86 ML <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Kees Cook <keescook@chromium.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Byungchul Park <byungchul.park@lge.com>
Subject: Re: [PATCH 10/19] x86/dumpstack: add get_stack_info() interface
Date: Tue, 26 Jul 2016 13:49:06 -0400	[thread overview]
Message-ID: <CAMzpN2ivhVynevNrbMarccWEa7=PbRsrbJ=weeFdCez2A5A8fw@mail.gmail.com> (raw)
In-Reply-To: <20160726164751.44xcnegpw2x3v2o6@treble>

On Tue, Jul 26, 2016 at 12:47 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Mon, Jul 25, 2016 at 05:09:44PM -0700, Andy Lutomirski wrote:
>> On Sat, Jul 23, 2016 at 7:04 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>> > Am I correct in understanding that there can only be one level of NMI
>> > nesting at any given time?  If so, could we make it easier on the
>> > unwinder by putting the nested NMI on a separate software stack, so the
>> > "next stack" pointers are always in the same place?  Or am I just being
>> > naive?
>>
>> I think you're being naive :)
>
> Another dumb question: since NMIs are reentrant, have you considered
> removing the NMI IST entry, and instead just have NMIs keep using the
> current stack?
>
> The first NMI could then be switched to an NMI software stack, like IRQs
> (assuming there's a way to do that atomically!).  And then determining
> the context of subsequent NMIs would be straightforward, and we'd no
> longer need to jump through all those horrible hoops in the entry code
> to deal with NMI nesting.
>
> Now you can tell me what else I'm missing...

There are several places (most notably SYSCALL entry) where the kernel
stack pointer is unsafe/user controlled for a brief time.  Since an
NMI can interrupt anywhere in the kernel, you have to use an IST to
protect against that case.

Blame Intel's legacy behavior for this mess, because IRET
unconditionally re-enables NMIs even if you are returning from another
exception like a page fault.  This wasn't a problem on the 8086 which
didn't have an MMU, but makes makes no sense on modern systems.

--
Brian Gerst

  reply	other threads:[~2016-07-26 17:49 UTC|newest]

Thread overview: 91+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-07-21 21:21 [PATCH 00/19] x86/dumpstack: rewrite x86 stack dump code Josh Poimboeuf
2016-07-21 21:21 ` [PATCH 01/19] x86/dumpstack: remove show_trace() Josh Poimboeuf
2016-07-21 21:49   ` Andy Lutomirski
2016-07-21 21:21 ` [PATCH 02/19] x86/dumpstack: add get_stack_pointer() and get_frame_pointer() Josh Poimboeuf
2016-07-21 21:53   ` Andy Lutomirski
2016-07-21 21:21 ` [PATCH 03/19] x86/dumpstack: remove unnecessary stack pointer arguments Josh Poimboeuf
2016-07-21 21:56   ` Andy Lutomirski
2016-07-22  1:41     ` Josh Poimboeuf
2016-07-22  2:29       ` Andy Lutomirski
2016-07-22  3:08       ` Brian Gerst
2016-07-21 21:21 ` [PATCH 04/19] x86/dumpstack: make printk_stack_address() more generally useful Josh Poimboeuf
2016-07-21 21:21 ` [PATCH 05/19] x86/dumpstack: fix function graph tracing stack dump reliability issues Josh Poimboeuf
2016-07-29 22:55   ` Steven Rostedt
2016-07-30  0:50     ` Josh Poimboeuf
2016-07-30  2:20       ` Steven Rostedt
2016-07-30 13:51         ` Josh Poimboeuf
2016-08-01 14:28           ` Steven Rostedt
2016-08-01 15:36             ` Josh Poimboeuf
2016-08-02 21:00               ` Josh Poimboeuf
2016-08-02 21:16                 ` Steven Rostedt
2016-08-02 22:13                   ` Josh Poimboeuf
2016-08-02 23:16                     ` Steven Rostedt
2016-08-03  1:56                       ` Josh Poimboeuf
2016-08-03  2:30                         ` Steven Rostedt
2016-08-03  2:50                           ` Josh Poimboeuf
2016-08-03  2:59                             ` Steven Rostedt
2016-08-03  3:12                               ` Josh Poimboeuf
2016-08-03  3:18                                 ` Steven Rostedt
2016-08-03  3:21                                   ` Steven Rostedt
2016-08-03  3:31                                     ` Josh Poimboeuf
2016-08-03  3:45                                       ` Steven Rostedt
2016-08-03 14:13                                         ` Josh Poimboeuf
2016-08-03  3:30                                   ` Josh Poimboeuf
2016-08-01 15:59     ` Josh Poimboeuf
2016-08-01 16:05       ` Steven Rostedt
2016-08-01 16:19         ` Josh Poimboeuf
2016-08-01 16:24     ` Josh Poimboeuf
2016-08-01 16:56       ` Steven Rostedt
2016-07-21 21:21 ` [PATCH 06/19] x86/dumpstack: remove extra brackets around "EOE" Josh Poimboeuf
2016-07-21 21:21 ` [PATCH 07/19] x86/dumpstack: add IRQ_USABLE_STACK_SIZE define Josh Poimboeuf
2016-07-21 22:01   ` Andy Lutomirski
2016-07-22  1:48     ` Josh Poimboeuf
2016-07-22  8:24       ` Ingo Molnar
2016-07-21 21:21 ` [PATCH 08/19] x86/dumpstack: don't disable preemption in show_stack_log_lvl() and dump_trace() Josh Poimboeuf
2016-07-21 21:21 ` [PATCH 09/19] x86/dumpstack: simplify in_exception_stack() Josh Poimboeuf
2016-07-21 22:05   ` Andy Lutomirski
2016-07-21 21:21 ` [PATCH 10/19] x86/dumpstack: add get_stack_info() interface Josh Poimboeuf
2016-07-22 23:26   ` Andy Lutomirski
2016-07-22 23:52     ` Andy Lutomirski
2016-07-23 13:09       ` Josh Poimboeuf
2016-07-22 23:54     ` Josh Poimboeuf
2016-07-23  0:15       ` Andy Lutomirski
2016-07-23 14:04         ` Josh Poimboeuf
2016-07-26  0:09           ` Andy Lutomirski
2016-07-26 16:26             ` Josh Poimboeuf
2016-07-26 17:51               ` Steven Rostedt
2016-07-26 18:56                 ` Josh Poimboeuf
2016-07-26 20:59               ` Andy Lutomirski
2016-07-26 22:24                 ` Josh Poimboeuf
2016-07-26 22:31                   ` Steven Rostedt
2016-07-26 22:37                   ` Andy Lutomirski
2016-07-26 16:47             ` Josh Poimboeuf
2016-07-26 17:49               ` Brian Gerst [this message]
2016-07-26 18:59                 ` Josh Poimboeuf
2016-07-21 21:21 ` [PATCH 11/19] x86/dumptrace: add new unwind interface and implementations Josh Poimboeuf
2016-07-21 21:21 ` [PATCH 12/19] perf/x86: convert perf_callchain_kernel() to the new unwinder Josh Poimboeuf
2016-07-21 21:21 ` [PATCH 13/19] x86/stacktrace: convert save_stack_trace_*() " Josh Poimboeuf
2016-07-21 21:21 ` [PATCH 14/19] oprofile/x86: convert x86_backtrace() " Josh Poimboeuf
2016-07-21 21:21 ` [PATCH 15/19] x86/dumpstack: convert show_trace_log_lvl() " Josh Poimboeuf
2016-07-21 21:49   ` Byungchul Park
2016-07-22  1:38     ` Josh Poimboeuf
2016-07-21 21:21 ` [PATCH 16/19] x86/dumpstack: remove dump_trace() Josh Poimboeuf
2016-07-21 21:21 ` [PATCH 17/19] x86/entry/dumpstack: encode pt_regs pointer in frame pointer Josh Poimboeuf
2016-07-21 22:27   ` Andy Lutomirski
2016-07-21 21:21 ` [PATCH 18/19] x86/dumpstack: print stack identifier on its own line Josh Poimboeuf
2016-07-21 21:21 ` [PATCH 19/19] x86/dumpstack: print any pt_regs found on the stack Josh Poimboeuf
2016-07-21 22:32   ` Andy Lutomirski
2016-07-22  3:30     ` Josh Poimboeuf
2016-07-22  5:13       ` Andy Lutomirski
2016-07-22 15:57         ` Josh Poimboeuf
2016-07-22 21:46           ` Andy Lutomirski
2016-07-22 22:20             ` Josh Poimboeuf
2016-07-22 23:18               ` Andy Lutomirski
2016-07-22 23:30                 ` Josh Poimboeuf
2016-07-22 23:39                   ` Andy Lutomirski
2016-07-23  0:00                     ` Josh Poimboeuf
2016-07-23  0:22 ` [PATCH 00/19] x86/dumpstack: rewrite x86 stack dump code Linus Torvalds
2016-07-23  0:31   ` Andy Lutomirski
2016-07-23  5:35     ` Josh Poimboeuf
2016-07-23  5:39       ` Linus Torvalds
2016-07-23 12:53         ` Josh Poimboeuf

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