From: Ingo Molnar <mingo@kernel.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Dave Hansen <dave.hansen@intel.com>,
David Woodhouse <dwmw2@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] x86/entry/64: Fix CR3 restore order in paranoid_exit()
Date: Wed, 14 Feb 2018 08:35:53 +0100 [thread overview]
Message-ID: <20180214073553.qsdnpetdgd4mkjdx@gmail.com> (raw)
In-Reply-To: <2b8ce3a31bcdfffa434269f4abf5d46816b75773.1518575248.git.jpoimboe@redhat.com>
* Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> I haven't actually seen any real-world bugs caused by this, so I'm not
> sure how theoretical it is. I just stumbled upon it in code review when
> looking for another bug.
I believe it's a real bug, but the fix is wrong with irq tracing or lockdep
enabled as Dave points out.
I think the reason we haven't seen this bug yet is that "paranoid" entry points
are limited to:
idtentry double_fault do_double_fault has_error_code=1 paranoid=2
idtentry debug do_debug has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK
idtentry int3 do_int3 has_error_code=0 paranoid=1 shift_ist=DEBUG_STACK
idtentry machine_check do_mce has_error_code=0 paranoid=1
Only machine_check is one that will interrupt an IRQS-off critical section
asynchronously - and machine check events are rare.
The other main asynchronous entries are NMI entries, which can be very high-freq
with perf profiling, but they are special: they don't use the 'idtentry' macro but
are open coded and restore user CR3 unconditionally so don't seem to have this
bug.
Thanks,
Ingo
prev parent reply other threads:[~2018-02-14 7:36 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-14 2:27 Josh Poimboeuf
2018-02-14 4:19 ` Dave Hansen
2018-02-14 7:39 ` Ingo Molnar
2018-02-14 16:11 ` Josh Poimboeuf
2018-02-14 22:27 ` Ingo Molnar
2018-02-14 16:13 ` Thomas Gleixner
2018-02-14 17:16 ` Andy Lutomirski
2018-02-14 23:31 ` [tip:x86/pti] x86/entry/64: Fix CR3 restore " tip-bot for Ingo Molnar
2018-02-15 0:31 ` tip-bot for Ingo Molnar
2018-02-14 7:35 ` Ingo Molnar [this message]
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