[8u/urgent] RFR: 8267689: [aarch64] Crash due to bad shift in indirect addressing mode

[Volker Simonis]

Hi,

sorry for the the "urgent" tag but I think this is a fix which is
worth while bringing into the next update release 8u302. This issue
was initially reported against Corretto 8
(https://github.com/corretto/corretto-8/issues/302), but it affects
all version of OpenJDK8u on aarch64. It can cause arbitrary crashes
due to incorrectly C2-generated code. We currently have two customer
who are affected by this issue and one of them reported back that the
proposed patch fixes the problem:

http://cr.openjdk.java.net/~simonis/webrevs/2021/8267689/
https://bugs.openjdk.java.net/browse/JDK-8267689

The JBS issue contains a detailed description on how this issue can be
reproduced (thanks to @charliegracie).

Notice that this issue only affects OpenJDK8u. In later releases it
was fixed by JDK-8154826 which completely reworked complex addressing
modes. Because that change doesn't apply cleanly (i.e. depends on
JDK-8136820, JDK-8034812, etc) and also affects other platforms I
suggest a point fix here which only fixes the current issue in jdk8u
instead of a downport.

The problem is that on aarch64, indirect loads and stores can accept
and index and a shift, but the shift has to correspond to the size of
the load/store operation (e.g. shift==2 for 32-bit operations and
shift==3 for 64-bit operations). Usage of sun.misc.Unsafe can lead to
address expressions which violate this requirement. They might for
example request a shift of "1" for a 32-bit operation. In the release
build, the generated code will nevertheless perform a 2-bit shift in
such a situation which can lead to arbitrary crashes at a later time.
In a debug build, the problem will be detected by the following
assertion:

assert(_ext.shift() == (int)size) failed: bad shift

This change only fixes the current issue in jdk8 by checking the shift
amount against the size of the memory operation in the Matcher and
rejects address modes where they don't conform. It borrows some code
like the `size_fits_all_mem_uses()` function from JDK-8154826 [1] but
uses it in more places because 8u has much more match rules which are
affected by the the bad pattern.

@roland sorry for calling you out explicitly, but I think as the
author of JDK-8154826u you would be the ideal Reviewer for this change
:)

Thank you and best regards,
Volker

[1] http://hg.openjdk.java.net/jdk9/jdk9/hotspot/rev/064d18bc1889