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Differential D7280

Add timingsafe_bcmp and timingsafe_memcmp.
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Authored by delphij on Jul 22 2016, 7:49 AM.
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rS304106: Add timingsafe_bcmp and timingsafe_memcmp.
Summary

Add timingsafe_bcmp and timingsafe_memcmp.

Obtained from: OpenBSD
MFC after: 1 month

Diff Detail

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rS FreeBSD src repository - subversion
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Buildable 4563
Build 4615: arc lint + arc unit

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delphij updated this revision to Diff 18653.Jul 22 2016, 7:49 AM
delphij retitled this revision from to Add timingsafe_bcmp and timingsafe_memcmp..
delphij updated this object.
delphij edited the test plan for this revision. (Show Details)
delphij added reviewers: jmg, trasz.
Herald added a reviewer: manpages. · View Herald TranscriptJul 22 2016, 7:49 AM
Herald added a subscriber: imp. · View Herald Transcript
delphij updated this revision to Diff 18654.Jul 22 2016, 7:51 AM
delphij edited edge metadata.

Fix typo.

Herald edited edge metadata. · View Herald TranscriptJul 22 2016, 7:51 AM
delphij added reviewers: secteam, security.Jul 22 2016, 7:52 AM
delphij updated this revision to Diff 18655.Jul 22 2016, 7:53 AM

Style.

Herald edited edge metadata. · View Herald TranscriptJul 22 2016, 7:53 AM
delphij updated this revision to Diff 18656.Jul 22 2016, 7:55 AM
delphij edited edge metadata.

Style in manpage.

Herald edited edge metadata. · View Herald TranscriptJul 22 2016, 7:55 AM
bjk added a subscriber: bjk.Jul 22 2016, 7:41 PM

I hate to bikeshed, but did we do any research on what names are used for constant-time functions elsewhere than OpenBSD?
Somehow I had the impression that a constant_time_ prefix was in use several places, though maybe that's just OpenSSL..

lib/libc/string/timingsafe_bcmp.3
19

Is this a target merge date? ;)

67

I slightly worry that future advances in compiler optimizers will make these semantics hard to support, but have no real objection.

eadler added a subscriber: eadler.Jul 22 2016, 10:22 PM

I wonder if it makes more sense to write this in asm than in C? Can we add
explicit "volatile" mentions here to ensure that optimizations don't occur?
If we can't write in asm, can we write a unit test to ensure the asm does
not get optimized out?

trasz accepted this revision.Jul 23 2016, 7:15 AM
trasz edited edge metadata.
This revision is now accepted and ready to land.Jul 23 2016, 7:15 AM
delphij added a comment.Jul 24 2016, 5:26 AM
In D7280#151588, @bjk wrote:

I hate to bikeshed, but did we do any research on what names are used for constant-time functions elsewhere than OpenBSD?
Somehow I had the impression that a constant_time_ prefix was in use several places, though maybe that's just OpenSSL..

Yes, but we already adopted timingsafe_bcmp in kernel...

delphij marked an inline comment as done.Jul 24 2016, 5:28 AM
delphij added inline comments.
lib/libc/string/timingsafe_bcmp.3
19

Yes.

67

That's possible, but I think we can always hint compiler not to optimize a select subset of library functions when this become a problem?

Closed by commit rS304106: Add timingsafe_bcmp and timingsafe_memcmp. (authored by delphij). · Explain WhyAug 14 2016, 11:39 PM
This revision was automatically updated to reflect the committed changes.
delphij marked an inline comment as done.

Revision Contents
Changeset List

PathSize
include/
2 lines
lib/
libc/
6 lines
string/
10 lines
5 lines
5 lines
3 lines
91 lines
36 lines
53 lines

Diff 18655

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include/string.h

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lib/libc/Versions.def

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lib/libc/string/Makefile.inc

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lib/libc/string/Symbol.map

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lib/libc/string/bcmp.3

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lib/libc/string/memcmp.3

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lib/libc/string/timingsafe_bcmp.3

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lib/libc/string/timingsafe_bcmp.c

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lib/libc/string/timingsafe_memcmp.c

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