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From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Eric Biggers <ebiggers@kernel.org>,
	Suren Baghdasaryan <surenb@google.com>,
	Johannes Weiner <hannes@cmpxchg.org>, Tejun Heo <tj@kernel.org>,
	Zefan Li <lizefan.x@bytedance.com>,
	Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Jonathan Corbet <corbet@lwn.net>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Cgroups <cgroups@vger.kernel.org>,
	stable <stable@vger.kernel.org>,
	Android Kernel Team <kernel-team@android.com>,
	syzbot <syzbot+cdb5dd11c97cc532efad@syzkaller.appspotmail.com>
Subject: Re: [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled
Date: Wed, 12 Jan 2022 12:06:04 +0100	[thread overview]
Message-ID: <Yd62HBixfq6jn6jR@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAHk-=wgwb6pJjvHYmOMT-yp5RYvw0pbv810Wcxdm5S7dWc-s0g@mail.gmail.com>

On Tue, Jan 11, 2022 at 11:11:32AM -0800, Linus Torvalds wrote:

> Of course, in practice, for pointers, the whole "dereference off a
> pointer" on the read side *does* imply a barrier in all relevant
> situations. So yes, a smp_store_release() -> READ_ONCE() does work in
> practice, although it's technically wrong (in particular, it's wrong
> on alpha, because of the completely broken memory ordering that alpha
> has that doesn't even honor data dependencies as read-side orderings)

On a tangent, that actually works, even on Alpha, see commit
d646285885154 ("alpha: Override READ_ONCE() with barriered
implementation").

WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Eric Biggers <ebiggers@kernel.org>,
	Suren Baghdasaryan <surenb@google.com>,
	Johannes Weiner <hannes@cmpxchg.org>, Tejun Heo <tj@kernel.org>,
	Zefan Li <lizefan.x@bytedance.com>,
	Ingo Molnar <mingo@redhat.com>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Jonathan Corbet <corbet@lwn.net>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Cgroups <cgroups@vger.kernel.org>,
	stable <stable@vger.kernel.org>,
	Android Kernel Team <kernel-team@android.com>, syzbot <syzb>
Subject: Re: [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled
Date: Wed, 12 Jan 2022 12:06:04 +0100	[thread overview]
Message-ID: <Yd62HBixfq6jn6jR@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAHk-=wgwb6pJjvHYmOMT-yp5RYvw0pbv810Wcxdm5S7dWc-s0g@mail.gmail.com>

On Tue, Jan 11, 2022 at 11:11:32AM -0800, Linus Torvalds wrote:

> Of course, in practice, for pointers, the whole "dereference off a
> pointer" on the read side *does* imply a barrier in all relevant
> situations. So yes, a smp_store_release() -> READ_ONCE() does work in
> practice, although it's technically wrong (in particular, it's wrong
> on alpha, because of the completely broken memory ordering that alpha
> has that doesn't even honor data dependencies as read-side orderings)

On a tangent, that actually works, even on Alpha, see commit
d646285885154 ("alpha: Override READ_ONCE() with barriered
implementation").

  parent reply	other threads:[~2022-01-12 11:06 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-11  7:12 [PATCH v2 1/1] psi: Fix uaf issue when psi trigger is destroyed while being polled Suren Baghdasaryan
2022-01-11 18:48 ` Eric Biggers
2022-01-11 19:11   ` Linus Torvalds
2022-01-11 19:11     ` Linus Torvalds
2022-01-11 19:26     ` Suren Baghdasaryan
2022-01-11 19:26       ` Suren Baghdasaryan
2022-01-11 19:34       ` Linus Torvalds
2022-01-11 19:34         ` Linus Torvalds
2022-01-11 19:41     ` Eric Biggers
2022-01-11 19:41       ` Eric Biggers
2022-01-11 19:45       ` Suren Baghdasaryan
2022-01-11 19:45         ` Suren Baghdasaryan
2022-01-11 20:14       ` Linus Torvalds
2022-01-11 20:14         ` Linus Torvalds
2022-01-11 23:37         ` Suren Baghdasaryan
2022-01-11 23:37           ` Suren Baghdasaryan
2022-01-12 11:06     ` Peter Zijlstra [this message]
2022-01-12 11:06       ` Peter Zijlstra
2022-01-18  6:58     ` Herbert Xu
2022-01-12 14:37 ` Johannes Weiner

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