Hi Peter,
On 6/24/14, 4:23 AM, Peter Levart wrote:
On 06/24/2014 01:45 AM, Coleen Phillimore wrote:
Please review a change to the JDK code for adding classLoader field
to the instances of java/lang/Class. This change restricts
reflection from changing access to the classLoader field. In the
spec, AccessibleObject.setAccessible() may throw SecurityException if
the accessibility of an object may not be changed:
http://docs.oracle.com/javase/7/docs/api/java/lang/reflect/AccessibleObject.html#setAccessible(boolean)
Only AccessibleObject.java has changes from the previous version of
this change.
open webrev at http://cr.openjdk.java.net/~coleenp/6642881_jdk_4/
bug link https://bugs.openjdk.java.net/browse/JDK-6642881
Thanks,
Coleen
Hi Coleen,
So hackers are prevented from hacking...
Out of curiosity, what would happen if someone changed the classLoader
field of some Class object? I guess VM still has it's own notion of
the class' class loader, right? Only the code that directly uses the
Class.getClassLoader() (and Unsafe.defineClass0) methods would be
affected...
True, Class.getClassLoader() calls would be affected but we may use this
call for security checks. I'm not really an expert on this, but we
thought it wouldn't be safe to allow user access to classLoader.
While we're at it, does this change in any way affect the GC logic?
Will GC now navigate the classLoader field during marking but
previously didn't ? Will this have any GC performance penalty ?
I actually ran this through our performance testing and got a good
improvement in one of the scimark benchmarks for no reason I could
explain (and lost the results), but none of the other tests were
affected. GC would have to mark this new field for full collections but
not young collections because it's only set during initialization. I
wouldn't expect this field to have any negative performance for GC.
Thanks,
Coleen
Regards, Peter
On 6/19/14, 11:01 PM, David Holmes wrote:
On 20/06/2014 6:53 AM, Joel Borggrén-Franck wrote:
Hi Mandy,
On 19 jun 2014, at 22:34, Mandy Chung <mandy.ch...@oracle.com> wrote:
On 6/19/14 12:34 PM, Joel Borggrén-Franck wrote:
Hi,
On 19 jun 2014, at 20:46, Coleen Phillimore
<coleen.phillim...@oracle.com> wrote:
On 6/17/14, 12:38 AM, Joel Borggrén-Franck wrote:
Have you considered hiding the Class.classLoader field from
reflection? I’m not sure it is necessary but I’m not to keen on
the idea of people poking at this field with Unsafe (which
should go away in 9 but …).
I don't know how to hide the field from reflection. It's a
private final field so you need to get priviledges to make it
setAccessible. If you mean injecting it on the JVM side, the
reason for this change is so that the JIT compilers can inline
this call and not have to call into the JVM to get the class
loader.
There is sun.reflect.Reflection.registerFieldsToFilter() that
hides a field from being found using reflection. It might very
well be the case that private and final is enough, I haven’t
thought this through 100%. On the other hand, is there a reason
to give users access through the field instead of having to use
Class.getClassLoader()?
There are many getter methods that returns a private final field.
I'm not sure if hiding the field is necessary nor a good precedence
to set. Accessing a private field requires "accessDeclaredMember"
permission although it's a different security check (vs
"getClassLoader"
permission). Arguably before this new classLoader field, one could
call Class.getClassLoader0() via reflection to get a hold of class
loader.
Perhaps you are concerned that the "accessDeclaredMember" permission
is too coarse-grained? I think the security team is looking into
the improvement in that regards.
I think I’m a bit worried about two things, first as you wrote,
“accessDeclaredMember” isn’t the same as “getClassLoader”, but
since you could get the class loader through getClassLoader0() that
shouldn’t be a new issue.
The second thing is that IIRC there are ways to set a final field
after initialization. I’m not sure we need to care about that
either if you need Unsafe to do it.
Normal reflection can set a final field if you can successfully call
setAccessible(true) on the Field object.
David
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cheers
/Joel