linux-kernel - RE: [PATCH] x86: Remove WARN_ON(in_nmi()) from vmalloc

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <27240C0AC20F114CBF8149A2696CBE4A01B64F02@SHSMSX101.ccr.corp.intel.com>
Date:	Thu, 17 Oct 2013 00:29:04 +0000
From:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
To:	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"Wang, Xiaoming" <xiaoming.wang@...el.com>,
	"Li, Zhuangzhi" <zhuangzhi.li@...el.com>
Subject: RE: [PATCH] x86: Remove WARN_ON(in_nmi()) from vmalloc_fault



> -----Original Message-----
> From: Ingo Molnar [mailto:mingo.kernel.org@...il.com] On Behalf Of Ingo
> Molnar
> Sent: Wednesday, October 16, 2013 8:51 PM
> To: Steven Rostedt
> Cc: LKML; Thomas Gleixner; H. Peter Anvin; Frederic Weisbecker; Andrew
> Morton; paulmck@...ux.vnet.ibm.com; Peter Zijlstra; x86@...nel.org; Wang,
> Xiaoming; Li, Zhuangzhi; Liu, Chuansheng
> Subject: Re: [PATCH] x86: Remove WARN_ON(in_nmi()) from vmalloc_fault
> 
> 
> * Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > On Wed, 16 Oct 2013 08:11:18 +0200
> > Ingo Molnar <mingo@...nel.org> wrote:
> >
> > >
> > > * Steven Rostedt <rostedt@...dmis.org> wrote:
> > >
> > > > Since the NMI iretq nesting has been fixed, there's no reason that
> > > > an NMI handler can not take a page fault for vmalloc'd code. No locks
> > > > are taken in that code path, and the software now handles nested NMIs
> > > > when the fault re-enables NMIs on iretq.
> > > >
> > > > Not only that, if the vmalloc_fault() WARN_ON_ONCE() is hit, and that
> > > > warn on triggers a vmalloc fault for some reason, then we can go into
> > > > an infinite loop (the WARN_ON_ONCE() does the WARN() before updating
> > > > the variable to make it happen "once").
> > > >
> > > > Reported-by: "Liu, Chuansheng" <chuansheng.liu@...el.com>
> > > > Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> > >
> > > Would be nice to see the warning quoted that triggered this.
> >
> > Sure, want me to add this to the change log?
> 
> Yeah, that would be helpful - but only the stack trace portion I suspect,
> to make it clear what caused the fault.
> 
> The one posted in the thread shows:
> 
> [   17.148755]  [<c2825b08>] do_page_fault+0x8/0x10
> [   17.153926]  [<c2823066>] error_code+0x5a/0x60
> [   17.158905]  [<c2825b00>] ? __do_page_fault+0x4a0/0x4a0
> [   17.164760]  [<c208d1a9>] ? module_address_lookup+0x29/0xb0
> [   17.170999]  [<c208dddb>] kallsyms_lookup+0x9b/0xb0
> [   17.186804]  [<c208def4>] sprint_symbol+0x14/0x20
> [   17.192063]  [<c208df1e>] __print_symbol+0x1e/0x40
> [   17.197430]  [<c25e00d7>] ? ashmem_shrink+0x77/0xf0
> [   17.202895]  [<c25e13e0>] ? logger_aio_write+0x230/0x230
> [   17.208845]  [<c205bdf5>] ? up+0x25/0x40
> [   17.213242]  [<c2039cb7>] ? console_unlock+0x337/0x440
> [   17.218998]  [<c2818236>] ? printk+0x38/0x3a
> [   17.223782]  [<c20006d0>] __show_regs+0x70/0x190
> [   17.228954]  [<c200353a>] show_regs+0x3a/0x1b0
> [   17.233931]  [<c2818236>] ? printk+0x38/0x3a
> [   17.238717]  [<c2824182>]
> arch_trigger_all_cpu_backtrace_handler+0x62/0x80
> [   17.246413]  [<c2823919>] nmi_handle.isra.0+0x39/0x60
> [   17.252071]  [<c2823a29>] do_nmi+0xe9/0x3f0
> 
> So kallsyms_lookup() faulted, while the NMI watchdog triggered a
> show_regs()? How is that possible?
Not NMI watchdog triggered show_regs(), when we call arch_trigger_all_cpu_backtrace(),
the NMI handler arch_trigger_all_cpu_backtrace_handler() will call show_regs().

> 
> Thanks,
> 
> 	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/