linux-kernel - Re: [patch 0/5] Support for sanitization flag in low-level page allocator

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Date:	Thu, 21 May 2009 15:08:15 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"Larry H." <research@...reption.com>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...l.org>, linux-mm@...ck.org,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [patch 0/5] Support for sanitization flag in low-level page allocator

Peter Zijlstra wrote:

> Seems like a particularly wasteful use of a pageflag. Why not simply
> erase the buffer before freeing in those few places where we know its
> important (ie. exactly those places you now put the pageflag in)?

You don't always know this at page free time.

I could see the PG_sensitive flag being used from
userspace through mmap or madvise flags.  This way
the sensitive memory from a program like gpg would
be cleaned, even if gpg died in a segfault accident.

I could also imagine the suspend-to-disk code skipping
PG_sensitive pages when storing data to disk, and
replacing it with some magic signature so programs
that use special PG_sensitive buffers can know that
their crypto key disappeared after a restore.

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