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Date: Thu, 7 Oct 2021 01:57:35 +0000
From: David Holland <>
Subject: Re: freezero() and freezeroall()

On Mon, Oct 04, 2021 at 06:22:39PM -0700, Alan Coopersmith wrote:
 > On 9/17/21 5:46 PM, Paul Eggert wrote:
 > > Looking at the current OpenBSD source code[1], it appears they're doing
 > > best effort. Unless I'm missing something, in some cases freezero
 > > appears to call memset instead of explicit_bzero. Even if that were
 > > changed, on real systems I expect the data are too often still lying
 > > around somewhere in the hardware. I suppose the idea is that it's
 > > better than nothing.
 > I believe the goal is to protect against the memory being visible
 > in core files and to debuggers, not to a physical RAM dump of some
 > sort.

(Probably should have said this a month ago)

I'm not sure I see the point of this function -- if you're calling
explicit_bzero because you're handling secrets, skipping the bzero
because the page is about to be unmapped seems like a mistake, so
explicit_bzero followed by free seems just as good as anything and
easier to reason about than adding something new.

If you're not handling secrets, then it seems like security theater.

David A. Holland

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