Re: [PATCH 0/3] explicit_bzero v5

["Michael Kerrisk (man-pages)" <mtk dot lists at gmail dot com>]

On 11/15/2016 07:54 PM, Zack Weinberg wrote:
> On Tue, Nov 15, 2016 at 1:42 PM, Florian Weimer <fweimer@redhat.com> wrote:
>> On 11/15/2016 07:02 PM, Paul Eggert wrote:
>>> On 11/15/2016 09:46 AM, Zack Weinberg wrote:
>>>
>>>> in any scenario where the arguments to explicit_bzero are visible to
>>>> malicious code, the adversary has already won.  Those arguments, after
>>>> all, are either in registers or on the stack.  If the adversary can
>>>> read either of those, they can already learn return addresses.
>>>
>>> It's possible that the adversary can read the stack but not registers
> 
> If the adversary can read the stack at all, I suspect they've already
> won, no matter what we do.
> 
>> I'm concerned that developers will read all these warnings and use memset
>> instead (or a hand-written loop) because this appears to avoid all these
>> issues.
> 
> Yeah, I'm actually worried that the warnings I already wrote are
> already too over-the-top.
> 
> cc:ing Michael Kerrisk - you write manpages all day, 

(Wouldn't it be great if someone did have that job :-). I don't.
But, I do write a lot of man pages...)

> does the
> documentation added in
> <https://sourceware.org/ml/libc-alpha/2016-11/msg00499.html> look like
> it would scare people off using the function at all?

So, I saw this message from you, Zack, went away and read the text
you point at, and then went back and started looking at other
people's messages in this thread. And I was struck by Florian's
comment, because I had exactly the same the same response. In fact,
worse: I was almost left worrying that explicit_bzero() creates
as many problems for me as it solves. I'll go back now and comment
on the actual document text.

Cheers,

Michael