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From: Thomas Gleixner <tglx@linutronix.de>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Will Deacon <will@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Mark Rutland <Mark.Rutland@arm.com>,
	Keno Fischer <keno@juliacomputing.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	kvm list <kvm@vger.kernel.org>,
	Gabriel Krisman Bertazi <krisman@collabora.com>
Subject: Re: [patch V3 01/13] entry: Provide generic syscall entry functionality
Date: Mon, 20 Jul 2020 08:50:02 +0200	[thread overview]
Message-ID: <87a6zuof39.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <A790AF9D-3BF7-4FEE-9E29-7C13FA3FE0C3@amacapital.net>

Andy Lutomirski <luto@amacapital.net> writes:
>> On Jul 19, 2020, at 3:17 AM, Thomas Gleixner <tglx@linutronix.de> wrote:
>> 
>> Andy Lutomirski <luto@kernel.org> writes:
>>>> On Sat, Jul 18, 2020 at 7:16 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>>>> Andy Lutomirski <luto@kernel.org> writes:
>>>>> FWIW, TIF_USER_RETURN_NOTIFY is a bit of an odd duck: it's an
>>>>> entry/exit word *and* a context switch word.  The latter is because
>>>>> it's logically a per-cpu flag, not a per-task flag, and the context
>>>>> switch code moves it around so it's always set on the running task.
>>>> 
>>>> Gah, I missed the context switch thing of that. That stuff is hideous.
>>> 
>>> It's also delightful because anything that screws up that dance (such
>>> as failure to do the exit-to-usermode path exactly right) likely
>>> results in an insta-root-hole.  If we fail to run user return
>>> notifiers, we can run user code with incorrect syscall MSRs, etc.
>> 
>> Looking at it deeper, having that thing in the loop is a pointless
>> exercise. This really wants to be done _after_ the loop.
>> 
> As long as we’re confident that nothing after the loop can set the flag again.

Yes, because that's the direct way off to user space.

Thanks,

        tglx

  reply	other threads:[~2020-07-20  6:50 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-16 18:22 [patch V3 00/13] entry, x86, kvm: Generic entry/exit functionality for host and guest Thomas Gleixner
2020-07-16 18:22 ` [patch V3 01/13] entry: Provide generic syscall entry functionality Thomas Gleixner
2020-07-16 20:52   ` Kees Cook
2020-07-16 21:55     ` Thomas Gleixner
2020-07-17 17:49       ` Kees Cook
2020-07-17 19:29         ` Thomas Gleixner
2020-07-17 21:56           ` Andy Lutomirski
2020-07-18 14:16             ` Thomas Gleixner
2020-07-18 14:41               ` Andy Lutomirski
2020-07-19 10:17                 ` Thomas Gleixner
2020-07-19 10:17                   ` Thomas Gleixner
2020-07-19 10:17                   ` Thomas Gleixner
2020-07-19 15:25                   ` Andy Lutomirski
2020-07-20  6:50                     ` Thomas Gleixner [this message]
2020-07-27 22:28   ` Andy Lutomirski
2020-07-16 18:22 ` [patch V3 02/13] entry: Provide generic syscall exit function Thomas Gleixner
2020-07-16 20:55   ` Kees Cook
2020-07-16 21:28     ` Thomas Gleixner
2020-07-16 18:22 ` [patch V3 03/13] entry: Provide generic interrupt entry/exit code Thomas Gleixner
2020-07-16 18:22 ` [patch V3 04/13] entry: Provide infrastructure for work before exiting to guest mode Thomas Gleixner
2020-07-16 18:22 ` [patch V3 05/13] x86/entry: Consolidate check_user_regs() Thomas Gleixner
2020-07-16 20:56   ` Kees Cook
2020-07-16 18:22 ` [patch V3 06/13] x86/entry: Consolidate 32/64 bit syscall entry Thomas Gleixner
2020-07-16 18:22 ` [patch V3 07/13] x86/ptrace: Provide pt_regs helpers for entry/exit Thomas Gleixner
2020-07-16 20:57   ` Kees Cook
2020-07-16 18:22 ` [patch V3 08/13] x86/entry: Use generic syscall entry function Thomas Gleixner
2020-07-16 21:13   ` Kees Cook
2020-07-16 21:33     ` Thomas Gleixner
2020-07-16 18:22 ` [patch V3 09/13] x86/entry: Use generic syscall exit functionality Thomas Gleixner
2020-07-16 18:22 ` [patch V3 10/13] x86/entry: Cleanup idtentry_entry/exit_user Thomas Gleixner
2020-07-16 18:22 ` [patch V3 11/13] x86/entry: Use generic interrupt entry/exit code Thomas Gleixner
2020-07-16 18:22 ` [patch V3 12/13] x86/entry: Cleanup idtentry_enter/exit Thomas Gleixner
2020-07-16 18:22 ` [patch V3 13/13] x86/kvm: Use generic exit to guest work function Thomas Gleixner

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