[botan-devel] version 1.10 and Valgrind

Yuri Schaeffer yuri at nlnetlabs.nl
Thu Jan 28 09:00:06 EST 2016


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Hi Jack,

> My best guess, given that this is occuring during the reseed step,
> is that RDRAND is not being handled by valgrind. From these bug
> reports
> 
> https://bugs.kde.org/show_bug.cgi?id=353370 
> https://bugs.launchpad.net/ubuntu/+source/valgrind/+bug/1501545

That guess was spot on it seems!

Thanks for the reference, that was truly helpful. I've now built the
latest Valgrind from svn trunk and its working as expected again.

(for reference: revision 15777)

Cheers,
Yuri

> this seems to be the case; valgrind 3.11's emulated CPU advertises 
> RDRAND support but does not implement it, causing a crash when the 
> application tries to execute it. The KDE bug contains a patch to 
> valgrind which clears the RDRAND bit, which was reported as fixing
> the problem for others and is already committed to valgrind trunk. 
> Apparently Valgrind 3.10 also works without issue.
> 
> If you're not running on a CPU which supports RDRAND then my guess
> goes completely out the window.
> 
> You can also work around this by building a new libbotan adding
> the configure.py flag `--disable-modules=rdrand`. There is not
> currently any way of disabling an entropy source at the application
> level without a rebuild (this is probably a bug...)
> 
> Best, Jack
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