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Date: Tue, 6 Jan 2015 20:42:26 +0100
From: Giel van Schijndel <me@mortis.eu>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: linux-kernel@vger.kernel.org, "David S. Miller" <davem@davemloft.net>,
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Subject: Re: [PATCH] Use memzero_explicit to clear local buffers
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On Mon, Jan 05, 2015 at 10:36:37 +1100, Herbert Xu wrote:
> On Sun, Jan 04, 2015 at 11:49:09PM +0100, Giel van Schijndel wrote:
>>
>>> sctx does not point to stack memory so this is bogus.
>>>=20
>>> Only stack memory cleared just before it goes out of scope needs
>>> memzero_explicit.
>>=20
>> Is that because the compiler can't safely optimize memset(0) away for a
>> variable with greater-than-local scope?
>=20
> Exactly.  memzero_explicit is not a marker for sensitive data.
> Its only purpose is to prevent the compiler from optimising away
> zeroing that occurs at the end of a scope.

Question: are you sure the compiler won't optimize the call to memset(0)
way if it's immediately followed by kfree()?

Because one of my changes concerns that situation.

Another actually does change a stack-allocated buffer, I'll split that
one off right away.

--=20
Met vriendelijke groet,
With kind regards,
Giel van Schijndel
--
"When all you have is a hammer, everything starts to look like a nail."
  -- Abraham Maslow

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