From: Thomas Gleixner <tglx@linutronix.de> To: Ira Weiny <ira.weiny@intel.com>, Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>, Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org, Andrew Morton <akpm@linux-foundation.org>, Fenghua Yu <fenghua.yu@intel.com>, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH RFC V2 17/17] x86/entry: Preserve PKRS MSR across exceptions Date: Thu, 23 Jul 2020 22:08:27 +0200 [thread overview] Message-ID: <87o8o6vvt0.fsf@nanos.tec.linutronix.de> (raw) In-Reply-To: <20200722052709.GB478587@iweiny-DESK2.sc.intel.com> Ira Weiny <ira.weiny@intel.com> writes: > On Fri, Jul 17, 2020 at 12:06:10PM +0200, Peter Zijlstra wrote: >> On Fri, Jul 17, 2020 at 12:20:56AM -0700, ira.weiny@intel.com wrote: > I've been really digging into this today and I'm very concerned that I'm > completely missing something WRT idtentry_enter() and idtentry_exit(). > > I've instrumented idt_{save,restore}_pkrs(), and __dev_access_{en,dis}able() > with trace_printk()'s. > > With this debug code, I have found an instance where it seems like > idtentry_enter() is called without a corresponding idtentry_exit(). This has > left the thread ref counter at 0 which results in very bad things happening > when __dev_access_disable() is called and the ref count goes negative. > > Effectively this seems to be happening: > > ... > // ref == 0 > dev_access_enable() // ref += 1 ==> disable protection > // exception (which one I don't know) > idtentry_enter() > // ref = 0 > _handler() // or whatever code... > // *_exit() not called [at least there is no trace_printk() output]... > // Regardless of trace output, the ref is left at 0 > dev_access_disable() // ref -= 1 ==> -1 ==> does not enable protection > (Bad stuff is bound to happen now...) Well, if any exception which calls idtentry_enter() would return without going through idtentry_exit() then lots of bad stuff would happen even without your patches. > Also is there any chance that the process could be getting scheduled and that > is causing an issue? Only from #PF, but after the fault has been resolved and the tasks is scheduled in again then the task returns through idtentry_exit() to the place where it took the fault. That's not guaranteed to be on the same CPU. If schedule is not aware of the fact that the exception turned off stuff then you surely get into trouble. So you really want to store it in the task itself then the context switch code can actually see the state and act accordingly. Thanks, tglx _______________________________________________ Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org To unsubscribe send an email to linux-nvdimm-leave@lists.01.org
WARNING: multiple messages have this Message-ID (diff)
From: Thomas Gleixner <tglx@linutronix.de> To: Ira Weiny <ira.weiny@intel.com>, Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>, Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org, Dan Williams <dan.j.williams@intel.com>, Vishal Verma <vishal.l.verma@intel.com>, Andrew Morton <akpm@linux-foundation.org>, Fenghua Yu <fenghua.yu@intel.com>, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH RFC V2 17/17] x86/entry: Preserve PKRS MSR across exceptions Date: Thu, 23 Jul 2020 22:08:27 +0200 [thread overview] Message-ID: <87o8o6vvt0.fsf@nanos.tec.linutronix.de> (raw) In-Reply-To: <20200722052709.GB478587@iweiny-DESK2.sc.intel.com> Ira Weiny <ira.weiny@intel.com> writes: > On Fri, Jul 17, 2020 at 12:06:10PM +0200, Peter Zijlstra wrote: >> On Fri, Jul 17, 2020 at 12:20:56AM -0700, ira.weiny@intel.com wrote: > I've been really digging into this today and I'm very concerned that I'm > completely missing something WRT idtentry_enter() and idtentry_exit(). > > I've instrumented idt_{save,restore}_pkrs(), and __dev_access_{en,dis}able() > with trace_printk()'s. > > With this debug code, I have found an instance where it seems like > idtentry_enter() is called without a corresponding idtentry_exit(). This has > left the thread ref counter at 0 which results in very bad things happening > when __dev_access_disable() is called and the ref count goes negative. > > Effectively this seems to be happening: > > ... > // ref == 0 > dev_access_enable() // ref += 1 ==> disable protection > // exception (which one I don't know) > idtentry_enter() > // ref = 0 > _handler() // or whatever code... > // *_exit() not called [at least there is no trace_printk() output]... > // Regardless of trace output, the ref is left at 0 > dev_access_disable() // ref -= 1 ==> -1 ==> does not enable protection > (Bad stuff is bound to happen now...) Well, if any exception which calls idtentry_enter() would return without going through idtentry_exit() then lots of bad stuff would happen even without your patches. > Also is there any chance that the process could be getting scheduled and that > is causing an issue? Only from #PF, but after the fault has been resolved and the tasks is scheduled in again then the task returns through idtentry_exit() to the place where it took the fault. That's not guaranteed to be on the same CPU. If schedule is not aware of the fact that the exception turned off stuff then you surely get into trouble. So you really want to store it in the task itself then the context switch code can actually see the state and act accordingly. Thanks, tglx
next prev parent reply other threads:[~2020-07-23 20:08 UTC|newest] Thread overview: 157+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-07-17 7:20 [PATCH RFC V2 00/17] PKS: Add Protection Keys Supervisor (PKS) support ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 01/17] x86/pkeys: Create pkeys_internal.h ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 02/17] x86/fpu: Refactor arch_set_user_pkey_access() for PKS support ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 8:54 ` Peter Zijlstra 2020-07-17 8:54 ` Peter Zijlstra 2020-07-17 20:52 ` Ira Weiny 2020-07-17 20:52 ` Ira Weiny 2020-07-20 9:14 ` Peter Zijlstra 2020-07-20 9:14 ` Peter Zijlstra 2020-07-17 22:36 ` Dave Hansen 2020-07-17 22:36 ` Dave Hansen 2020-07-20 9:13 ` Peter Zijlstra 2020-07-20 9:13 ` Peter Zijlstra 2020-07-17 7:20 ` [PATCH RFC V2 03/17] x86/pks: Enable Protection Keys Supervisor (PKS) ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 04/17] x86/pks: Preserve the PKRS MSR on context switch ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 8:31 ` Peter Zijlstra 2020-07-17 8:31 ` Peter Zijlstra 2020-07-17 21:39 ` Ira Weiny 2020-07-17 21:39 ` Ira Weiny 2020-07-17 8:59 ` Peter Zijlstra 2020-07-17 8:59 ` Peter Zijlstra 2020-07-17 22:34 ` Ira Weiny 2020-07-17 22:34 ` Ira Weiny 2020-07-20 9:15 ` Peter Zijlstra 2020-07-20 9:15 ` Peter Zijlstra 2020-07-20 18:35 ` Ira Weiny 2020-07-20 18:35 ` Ira Weiny 2020-07-17 7:20 ` [PATCH RFC V2 05/17] x86/pks: Add PKS kernel API ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 06/17] x86/pks: Add a debugfs file for allocated PKS keys ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 07/17] Documentation/pkeys: Update documentation for kernel pkeys ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 08/17] x86/pks: Add PKS Test code ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 09/17] memremap: Convert devmap static branch to {inc,dec} ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 10/17] fs/dax: Remove unused size parameter ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 11/17] drivers/dax: Expand lock scope to cover the use of addresses ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 12/17] memremap: Add zone device access protection ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 9:10 ` Peter Zijlstra 2020-07-17 9:10 ` Peter Zijlstra 2020-07-18 5:06 ` Ira Weiny 2020-07-18 5:06 ` Ira Weiny 2020-07-20 9:16 ` Peter Zijlstra 2020-07-20 9:16 ` Peter Zijlstra 2020-07-17 9:17 ` Peter Zijlstra 2020-07-17 9:17 ` Peter Zijlstra 2020-07-18 5:51 ` Ira Weiny 2020-07-18 5:51 ` Ira Weiny 2020-07-17 9:20 ` Peter Zijlstra 2020-07-17 9:20 ` Peter Zijlstra 2020-07-17 7:20 ` [PATCH RFC V2 13/17] kmap: Add stray write protection for device pages ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 9:21 ` Peter Zijlstra 2020-07-17 9:21 ` Peter Zijlstra 2020-07-19 4:13 ` Ira Weiny 2020-07-19 4:13 ` Ira Weiny 2020-07-20 9:17 ` Peter Zijlstra 2020-07-20 9:17 ` Peter Zijlstra 2020-07-21 16:31 ` Ira Weiny 2020-07-21 16:31 ` Ira Weiny 2020-07-17 7:20 ` [PATCH RFC V2 14/17] dax: Stray write protection for dax_direct_access() ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 9:22 ` Peter Zijlstra 2020-07-17 9:22 ` Peter Zijlstra 2020-07-19 4:41 ` Ira Weiny 2020-07-19 4:41 ` Ira Weiny 2020-07-17 7:20 ` [PATCH RFC V2 15/17] nvdimm/pmem: Stray write protection for pmem->virt_addr ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 7:20 ` [PATCH RFC V2 16/17] [dax|pmem]: Enable stray write protection ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 9:25 ` Peter Zijlstra 2020-07-17 9:25 ` Peter Zijlstra 2020-07-17 7:20 ` [PATCH RFC V2 17/17] x86/entry: Preserve PKRS MSR across exceptions ira.weiny 2020-07-17 7:20 ` ira.weiny 2020-07-17 9:30 ` Peter Zijlstra 2020-07-17 9:30 ` Peter Zijlstra 2020-07-21 18:01 ` Ira Weiny 2020-07-21 18:01 ` Ira Weiny 2020-07-21 19:11 ` Peter Zijlstra 2020-07-21 19:11 ` Peter Zijlstra 2020-07-17 9:34 ` Peter Zijlstra 2020-07-17 9:34 ` Peter Zijlstra 2020-07-17 10:06 ` Peter Zijlstra 2020-07-17 10:06 ` Peter Zijlstra 2020-07-22 5:27 ` Ira Weiny 2020-07-22 5:27 ` Ira Weiny 2020-07-22 9:48 ` Peter Zijlstra 2020-07-22 9:48 ` Peter Zijlstra 2020-07-22 21:24 ` Ira Weiny 2020-07-22 21:24 ` Ira Weiny 2020-07-23 20:08 ` Thomas Gleixner [this message] 2020-07-23 20:08 ` Thomas Gleixner 2020-07-23 20:15 ` Thomas Gleixner 2020-07-23 20:15 ` Thomas Gleixner 2020-07-24 17:23 ` Ira Weiny 2020-07-24 17:23 ` Ira Weiny 2020-07-24 17:29 ` Andy Lutomirski 2020-07-24 17:29 ` Andy Lutomirski 2020-07-24 19:43 ` Ira Weiny 2020-07-24 19:43 ` Ira Weiny 2020-07-22 16:21 ` Andy Lutomirski 2020-07-22 16:21 ` Andy Lutomirski 2020-07-22 16:21 ` Andy Lutomirski 2020-07-23 16:18 ` Fenghua Yu 2020-07-23 16:18 ` Fenghua Yu 2020-07-23 16:18 ` Fenghua Yu 2020-07-23 16:23 ` Dave Hansen 2020-07-23 16:23 ` Dave Hansen 2020-07-23 16:23 ` Dave Hansen 2020-07-23 16:52 ` Fenghua Yu 2020-07-23 16:52 ` Fenghua Yu 2020-07-23 16:52 ` Fenghua Yu 2020-07-23 17:08 ` Andy Lutomirski 2020-07-23 17:08 ` Andy Lutomirski 2020-07-23 17:08 ` Andy Lutomirski 2020-07-23 17:30 ` Dave Hansen 2020-07-23 17:30 ` Dave Hansen 2020-07-23 17:30 ` Dave Hansen 2020-07-23 20:23 ` Thomas Gleixner 2020-07-23 20:23 ` Thomas Gleixner 2020-07-23 20:23 ` Thomas Gleixner 2020-07-23 20:22 ` Thomas Gleixner 2020-07-23 20:22 ` Thomas Gleixner 2020-07-23 20:22 ` Thomas Gleixner 2020-07-23 21:30 ` Andy Lutomirski 2020-07-23 21:30 ` Andy Lutomirski 2020-07-23 21:30 ` Andy Lutomirski 2020-07-23 22:14 ` Thomas Gleixner 2020-07-23 22:14 ` Thomas Gleixner 2020-07-23 22:14 ` Thomas Gleixner 2020-07-23 19:53 ` Thomas Gleixner 2020-07-23 19:53 ` Thomas Gleixner 2020-07-23 22:04 ` Ira Weiny 2020-07-23 22:04 ` Ira Weiny 2020-07-23 23:41 ` Thomas Gleixner 2020-07-23 23:41 ` Thomas Gleixner 2020-07-24 21:24 ` Thomas Gleixner 2020-07-24 21:24 ` Thomas Gleixner 2020-07-24 21:31 ` Thomas Gleixner 2020-07-24 21:31 ` Thomas Gleixner 2020-07-25 0:09 ` Andy Lutomirski 2020-07-25 0:09 ` Andy Lutomirski 2020-07-25 0:09 ` Andy Lutomirski 2020-07-27 20:59 ` Ira Weiny 2020-07-27 20:59 ` Ira Weiny 2020-07-24 22:19 ` [PATCH RFC V2 00/17] PKS: Add Protection Keys Supervisor (PKS) support Kees Cook 2020-07-24 22:19 ` Kees Cook
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=87o8o6vvt0.fsf@nanos.tec.linutronix.de \ --to=tglx@linutronix.de \ --cc=akpm@linux-foundation.org \ --cc=bp@alien8.de \ --cc=dave.hansen@linux.intel.com \ --cc=fenghua.yu@intel.com \ --cc=ira.weiny@intel.com \ --cc=linux-doc@vger.kernel.org \ --cc=linux-fsdevel@vger.kernel.org \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-kselftest@vger.kernel.org \ --cc=linux-mm@kvack.org \ --cc=linux-nvdimm@lists.01.org \ --cc=luto@kernel.org \ --cc=mingo@redhat.com \ --cc=peterz@infradead.org \ --cc=x86@kernel.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.