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Date: Wed, 04 Oct 2017 20:29:15 -0400
From: Daniel Micay <danielmicay@...il.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>, "Roberts, William C"
	 <william.c.roberts@...el.com>, Tejun Heo <tj@...nel.org>
Cc: Jordan Glover <Golden_Miller83@...tonmail.ch>, "Tobin C. Harding"
 <me@...in.cc>, 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>, 
 "kernel-hardening@...ts.openwall.com"
 <kernel-hardening@...ts.openwall.com>, Catalin Marinas
 <catalin.marinas@....com>,  Will Deacon <will.deacon@....com>, Steven
 Rostedt <rostedt@...dmis.org>, Chris Fries <cfries@...gle.com>,  Dave
 Weinstein <olorin@...gle.com>
Subject: Re: [RFC V2 0/6] add more kernel pointer filter
 options

On Wed, 2017-10-04 at 16:52 -0700, Linus Torvalds wrote:
> On Wed, Oct 4, 2017 at 2:58 PM, Roberts, William C
> <william.c.roberts@...el.com> wrote:
> > 
> > I agree with you 100% kptr restrict is odd, and I don't think anyone
> > should have had to opt in to be
> > cleansed via kptr_restrict value via %pK. Opt-in never works. One
> > nice thing now, is that checkpatch
> > has checking of %p usages and warns.
> 
> Yeah, the checkpatch thing may help for future patches.
> 
> > As far as broken things, I can't comment on desktop systems where I
> > think it's harder to make that claim.
> > I see value in embedded systems where I am shipping the whole image,
> > So I know when/what will
> > break.
> > 
> > If this was in-tree, Android would be setting this to 4 immediately
> > FWIW.
> 
> Does android set it to 2 right now?

Yes, as the universal baseline.

On Google Pixels it's set to this 4 level since August (Android 8.0)
which indicates they plan on moving to that universally.

They only allow dmesg access for core system services so I think their
concern is with formatted strings leaking it elsewhere, not to dmesg.

These are the only services they allow to read dmesg:

private/system_server.te:  allow system_server kernel:system syslog_read;
public/dumpstate.te:allow dumpstate kernel:system syslog_read;
public/init.te:allow init kernel:system syslog_read;
public/logd.te:allow logd kernel:system syslog_read;
public/recovery.te:  allow recovery kernel:system syslog_read;

logd doesn't read it in production builds, but even when it does in
engineering builds it only gives out access to privileged apps with
READ_LOGS which isn't something a third party app can obtain.

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