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Date: Wed, 28 Feb 2018 11:34:00 +0530 (IST)
From: P J P <ppandit@...hat.com>
To: Kees Cook <keescook@...omium.org>
cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Florian Weimer <fweimer@...hat.com>, P J P <pjp@...oraproject.org>,
Laura Abbott <labbott@...hat.com>
Subject: Re: [PATCH 0/1] Zero initialise kernel stack variables
Hello Kees, Laura,
Thank you so much for the kind review, I appreciate it.
+-- On Tue, 27 Feb 2018, Kees Cook wrote --+
| Unfortunately "noticeable" isn't going to be a viable metric. You'll need to
| do some real-world benchmarks (i.e. kernel builds, hackbench, etc), and
| compare the results.
Yes, okay. I'll do this exercise and get back with the results.
| Even just initializing passed-by-reference variables
| (GCC_PLUGIN_STRUCTLEAK_BYREF_ALL) had measurable performance impact.
I see.
| It would be nice to have four options/features available from the
| compiler, from least to most performance impact:
|
| - initialize padding to zero when static initializers are used (this would
| make foo = { .field = something }; identical to memset(&foo, 0,
| sizeof(foo)); foo.field = something for all structures, but now, any
| structures with padding _must_ use the latter to be safe, which is highly
| error-prone).
|
| - initialize all uninitialized variables that contain a structure marked
| with a special attribute (e.g. __attribute__((force_initialize)) ).
|
| - initialize all uninitialized variables that are passed by reference (see
| GCC_PLUGIN_STRUCTLEAK_BYREF_ALL).
|
| - initialize all uninitialized variables (-finit-local-vars seems to do
| this)
I see, will check about these.
| > The patch here adds a kbuild menu option to enable/disable '-finit-local-vars'
| > compiler flag while building the Linux kernel.
|
| Since this is a single patch, I think it'd be better to fold this
| entire cover letter into patch 1.
Right, okay.
Thank you so much.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F
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