From: Denys Vlasenko <vda.linux@googlemail.com>
To: musl <musl@lists.openwall.com>
Cc: gcc@gcc.gnu.org, llvmdev@cs.uiuc.edu,
GNU C Library <libc-alpha@sourceware.org>
Subject: Re: Compiler support for erasure of sensitive data
Date: Thu, 22 Oct 2015 18:09:31 +0200 [thread overview]
Message-ID: <CAK1hOcMx+ibdoEE95h2R5+y6Znf1S4X0cSq-s3Nv+cuRk5-DuA@mail.gmail.com> (raw)
In-Reply-To: <55F05FF1.3000405@panix.com>
On Wed, Sep 9, 2015 at 6:36 PM, Zack Weinberg <zackw@panix.com> wrote:
> The first, simpler problem is strictly optimization. explicit_bzero
> can be optimized to memset followed by a vacuous use of the memory
> region (generating no machine instructions, but preventing the stores
> from being deleted as dead); this is valuable because the sensitive
> data is often small and fixed-size, so the memset can in turn be
> replaced by inline code.
How valuable is that speedup due to possible inlining?
You know, call instruction is not a crime.
In fact, it is *heavily* optimized on any CPU exactly because
calls happen gazillion times every second.
In my measurement, on x86 call+ret pair is cheaper than
a single read-modify-write ALU op on L1 data item!
So, just implement explicit_bzero() as a function which
is prohibited from inlining, and which clears all call-clobbered
registers in addition to clearing memory.
This will probably also be the smallest solution code size wise.
prev parent reply other threads:[~2015-10-22 16:09 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-09 16:36 Zack Weinberg
2015-09-09 16:39 ` Fwd: " Zack Weinberg
2015-09-09 16:41 ` Zack Weinberg
2015-09-09 16:42 ` Rich Felker
2015-09-09 16:47 ` [musl] " Zack Weinberg
2015-09-09 17:13 ` Rich Felker
2015-09-09 18:48 ` [musl] " Zack Weinberg
2015-09-09 20:05 ` Rich Felker
2015-09-09 16:52 ` Paul_Koning
2015-09-09 16:58 ` Zack Weinberg
2015-09-09 17:25 ` [musl] " Rich Felker
2015-09-09 17:54 ` David Edelsohn
2015-09-09 18:02 ` Paul_Koning
2015-09-09 18:11 ` David Edelsohn
2015-09-09 19:03 ` Zack Weinberg
2015-09-09 20:26 ` Szabolcs Nagy
2015-10-22 16:02 ` [musl] " Denys Vlasenko
2015-10-22 16:09 ` Denys Vlasenko [this message]
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