Date: Wed, 25 Oct 2017 06:00:21 +0200 From: "Jason A. Donenfeld" <Jason@...c4.com> To: "Tobin C. Harding" <me@...in.cc> Cc: kernel-hardening@...ts.openwall.com, "Theodore Ts'o" <tytso@....edu>, Linus Torvalds <torvalds@...ux-foundation.org>, Kees Cook <keescook@...omium.org>, Paolo Bonzini <pbonzini@...hat.com>, Tycho Andersen <tycho@...ker.com>, "Roberts, William C" <william.c.roberts@...el.com>, Tejun Heo <tj@...nel.org>, Jordan Glover <Golden_Miller83@...tonmail.ch>, Greg KH <gregkh@...uxfoundation.org>, Petr Mladek <pmladek@...e.com>, Joe Perches <joe@...ches.com>, Ian Campbell <ijc@...lion.org.uk>, Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <wilal.deacon@....com>, Steven Rostedt <rostedt@...dmis.org>, Chris Fries <cfries@...gle.com>, Dave Weinstein <olorin@...gle.com>, Daniel Micay <danielmicay@...il.com>, Djalal Harouni <tixxdz@...il.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v7] printk: hash addresses printed with %p On Wed, Oct 25, 2017 at 5:49 AM, Tobin C. Harding <me@...in.cc> wrote: > static_branch_disable(&no_ptr_secret) : Doesn't sleep, just atomic read > and set and maybe a WARN_ONCE. Are you sure about that? I just looked myself, and though there is a !HAVE_JUMP_LABEL ifdef that does what you described, there's also a HAVE_JUMP_LABEL that takes a mutex, which sleeps: static_branch_disable static_key_disable cpus_read_lock percpu_down_read percpu_down_read_preempt_disable might_sleep > Now for the 'executes from process context' stuff. Er, sorry, I meant to write non-process context in my original message, which is generally where you're worried about sleeping. > If the callback mechanism is utilized (i.e print before randomness is > ready) then the call back will be executed the next time the randomness > pool gets added to So it sounds to me like this might be called in non-process context. Disaster. I realize the static_key thing was my idea in the original email, so sorry for leading you astray. But moving to do this in early_initcall wound up fixing other issues too, so all and all a net good in going this direction. Two options: you stick with static_branch, because it's cool and speed is fun, and work around all of the above with a call to queue_work so that static_branch_enable is called only from process context. Or, you give up on static_key, because it's not actually super necessary, and instead just use an atomic, and reason that using `if (unlikely(!atomic_read(&whatever)))` is probably good enough. In this option, the code would be pretty much the same as v7, except you'd s/static_branch/atomic_t/, and change the helpers, etc. This is probably the more reasonable way.
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.