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Date: Thu, 5 Oct 2017 10:10:43 -0700
From: Dave Weinstein <>
To: Linus Torvalds <>
Cc: "Roberts, William C" <>, "Tobin C. Harding" <>, Tejun Heo <>, 
	Jordan Glover <>, Greg KH <>, 
	Petr Mladek <>, Joe Perches <>, Ian Campbell <>, 
	Sergey Senozhatsky <>, 
	"" <>, 
	Catalin Marinas <>, Will Deacon <>, 
	Steven Rostedt <>, Chris Fries <>
Subject: Re: [RFC V2 0/6] add more kernel pointer filter options

> Does android set it to 2 right now?

Yes. And as of Android 8.0, it will attempt to set it to 4, and step back
to 2 if the higher restriction values are not supported (

>     We already don't get great bug reports. If we now start getting

>bug reports and tell users "recreate this with 'kptr_enabled' on the

>kernel command line" because some debug message didn't give proper

>data, that will just result in us getting even less bug reports.

This is why the original Android patch set whitelists the stack traces --
it was a deliberate choice to make sure that kernel bug reports were
generally meaningful by default.

>Honestly, what's the difference between setting kptr_restrict to 4 and

>just using a sed-script (or maybe some coccinelle) to remove all

>existing plain %p users?

The primary benefit from my perspective is that the userland component can
establish a general expectation of the level of information disclosure that
depends on a single feature being implemented, rather than an arbitrarily
large number of point fixes across multiple kernel versions.


Dave Weinstein
Android SDL

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