Hello again,
Resurrecting this review. It is now part of proposed JEP and some
details have changed. The alternate jvm variant is now called
"nonspeculative", and so is activated with the command line flag
"-nonspeculative". This is all in line with the proposed JEP.
Differences from last webrev are:
* The name of the new JVM variant
* Removed an unused AC_SUBST
Webrev: http://cr.openjdk.java.net/~erikj/8202384/webrev.07/index.html
/Erik
On 2018-06-11 23:29, Magnus Ihse Bursie wrote:
On 2018-06-11 22:42, Erik Joelsson wrote:
Hello,
Based on the discussion here, I have reverted back to something more
similar to webrev.02, but with a few changes. Mainly fixing a bug
that caused JVM_FEATURES_hardened to not actually be the same as for
server (if you have custom additions in configure). I also added a
check so that configure fails if you try to enable either variant
hardened or feature no-speculative-cti and the flags aren't available.
Webrev: http://cr.openjdk.java.net/~erikj/8202384/webrev.05/index.html
Looks good to me. Thanks for all the effort!
/Magnus
/Erik
On 2018-06-11 00:10, Magnus Ihse Bursie wrote:
On 2018-06-08 23:50, Erik Joelsson wrote:
On 2018-06-07 17:30, David Holmes wrote:
On 8/06/2018 6:11 AM, Erik Joelsson wrote:
I just don't think the extra work is warranted or should be
prioritized at this point. I also cannot think of a combination
of options required for what you are suggesting that wouldn't be
confusing to the user. If someone truly feels like these flags
are forced on them and can't live with them, we or preferably
that person can fix it then. I don't think that's dictatorship.
OpenJDK is still open source and anyone can contribute.
I don't see why --enable-hardened-jdk and
--enable-hardened-hotspot to add to the right flags would be
either complicated or confusing.
For me the confusion surrounds the difference between
--enable-hardened-hotspot and --with-jvm-variants=server, hardened
and making the user understand it. But sure, it is doable. Here is
a new webrev with those two options as I interpret them. Here is
the help text:
--enable-hardened-jdk enable hardenening compiler flags for all jdk
libraries (except the JVM), typically
disabling
speculative cti. [disabled]
--enable-hardened-hotspot
enable hardenening compiler flags for
hotspot (all
jvm variants), typically disabling
speculative cti.
To make hardening of hotspot a runtime
choice,
consider the "hardened" jvm variant
instead of this
option. [disabled]
Note that this changes the default for jdk libraries to not enable
hardening unless the user requests it.
Webrev: http://cr.openjdk.java.net/~erikj/8202384/webrev.04/
Hold it, hold it! I'm not sure how we ended up here, but I don't
like it at all. :-(
I think Eriks initial patch is much better than this. Some arguments
in random order to defend this position:
1) Why should we have a configure option to disable security
relevant flags for the JDK, if there has been no measured negative
effect? We don't do this for any other compiler flags, especially
not security relevant ones!
I've re-read the entire thread to see if I could understand what
could possibly motivate this, but the only thing I can find is David
Holmes vague fear that these flags would not be well-tested enough.
Let me counter with my own vague guesses: I believe the spectre
mitigation methods to have been fully and properly tested, since
they are rolled-out massively on all products. And let me complement
with my own fear: the PR catastrophe if OpenJDK were *not* built
with spectre mitigations, and someone were to exploit that!
In fact, I could even argue that "server" should be hardened *by
default*, and that we should instead introduce a non-hardened JVM
named something akin to "quick-but-dangerous-server" instead. But I
realize that a 25% performance hit is hard to swallow, so I won't
push this agenda.
2) It is by no means clear that "--enable-hardened-jdk" does not
harden all aspects of the JDK! If we should keep the option (which I
definitely do not think we should!) it should be renamed to
"--enable-hardened-libraries", or something like that. And it should
be on by default, so it should be a
"--disabled-hardened-jdk-libraries".
Also, the general-sounding name "hardened" sounds like it might
encompass more things than it does. What if I disabled a hardened
jdk build, should I still get stack banging protection? If so, you
need to move a lot more security-related flags to this option. (And,
just to be absolutely clear: I don't think you should do that.)
3) Having two completely different ways of turning on Spectre
protection for hotspot is just utterly confusing! This was a perfect
example of how to use the JVM features, just as in the original patch.
If you want to have spectre mitigation enabled for both server and
client, by default, you would just need to run "configure
--with-jvm-variants=server,client
--with-jvm-features=no-speculative-cti", which will enable that
feature for all variants. That's not really hard *at all* for anyone
building OpenJDK. And it's way clearer what will happen, than a
--enable-hardened-hotspot.
4) If you are a downstream provider building OpenJDK and you are
dead set on not including Spectre mitigations in the JDK libraries,
despite being shown to have no negative effects, then you can do
just as any other downstream user with highly specialized
requirements, and patch the source. I have no sympathies for this; I
can't stop it but I don't think there's any reason for us to
complicate the code to support this unlikely case.
So, to recap, I think the webrev as published in
http://cr.openjdk.java.net/~erikj/8202384/webrev.02/ (with
"altserver" renamed to "hardened") is the way to go.
/Magnus
/Erik
