RFR(S) 7127066: Class verifier accepts an invalid class file

Karen Kinnear karen.kinnear at oracle.com
Thu Mar 19 19:33:13 UTC 2015


I get it - this only affects instructions that set the type of a local slot since the operand stack is cleared.

So - what about istore?
If we have a local slot that contains a long or double, Frederic reminded me that JVMS 2.6.1 does allow stores to those separate slots,
e.g. an istore. My mental model of this is that it would change the type of the local slot.

Would that mean we would want to check any of the *store bytecodes?

(I know the spec would change for all bytecodes which might be cleaner - I suspect you are being extra cautious about making changes
to reduce risk of breaking something in the field).


On Mar 18, 2015, at 2:18 PM, harold seigel wrote:

> Hi Karen,
> The fix does not affect normal verifier type-state (stack map) checking that is done when looping through the bytecodes.  It only affects whether the incoming or outgoing type-state is used when comparing the type-state at a particular bytecode with the type-state at the start of its potential exception handlers.
> In addition, (to paraphrase Keith's comment in the bug), it only affects instructions that set the type of a local slot (astore and friends) ... .  Instructions that affect the expression stack are not a problem since the type-state's stack is cleared when type checking an exception handler.
> So, other bytecodes such as aload and friends, getstatic and getfield, etc.  are not an issue.
> Thanks, Harold
> On 3/16/2015 3:49 PM, Karen Kinnear wrote:
>> Harold,
>> Thanks for helping me walk through this in more detail.
>> The way I read this, the fix would apply to all bytecodes - except for
>> invokespecial <init> - which is handled I believe correctly inside the
>> verify_invoke_init.
>> So if you could possibly experiment with some additional instructions - I suspect
>> you can make a conditional check where you put the beginning check and remove
>> the check at the end.
>> thanks,
>> Karen
>> On Mar 15, 2015, at 8:58 PM, David Holmes wrote:
>>> Hi Harold,
>>> On 14/03/2015 4:06 AM, harold seigel wrote:
>>>> Hi,
>>>> Please review this fix for bug JDK-7127066.  The fix applies to astore*
>>>> bytecodes because, when inside an exception handler, they can reference
>>>> the thrown object and modify the number of stack locals, enabling the
>>>> incorrect stack match.
>>>> Open webrev: http://oklahoma.us.oracle.com/~hseigel/webrev/bug_7127066/
>>>> JBS bug: https://bugs.openjdk.java.net/browse/JDK-7127066
>>>> The fix was tested with JCK api, lang, and vm tests, jtreg hotspot,
>>>> java/lang, java/io, and java/util tests, and testbase quick and split
>>>> verifier tests, and with the test case provided in the bug.
>>> The new check looks okay, though I can't verify the exact placement of it.
>>> Thanks,
>>> David
>>>> Thanks! Harold

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