RFR (S) JDK-7107135 - Stack guard pages becomes writable
Ioi Lam
ioi.lam at oracle.com
Wed Feb 27 18:31:48 PST 2013
I have updated the patch:
http://javaweb.us.oracle.com/~iklam/webrev/7107135/stack_guard_002/
The only changes since the last version are in os_linux.cpp,
os_linux_x86.cpp
and os_linux_sparc.cpp.
1. Added assert in (is_init_completed()==false) case that no Java
threads have
been created (line 1867 os_linux.cpp)
2. Avoid unnecessary condition checks in os::Linux::dll_load_inner()
3. Print a diagnostic message when we crash the native stack to suggest
the user
check for executable stack .so files.
I also restored the SAP copyright in the test sources.
- Ioi
On 02/27/2013 03:03 PM, Ioi Lam wrote:
> On 02/21/2013 07:07 PM, David Holmes wrote:
>> <fixed the subject to try and get the email thread to flow >
>>
>> On 22/02/2013 1:29 AM, Zhengyu Gu wrote:
>>> Hi Ioi,
>>>
>>> 1. os_linux.cpp #1877 : this will restrict os::dll_load() caller to
>>> Java
>>> thread only, is it ok?
>>
>> That bit doesn't make sense to me:
>>
>> 1877 ThreadInVMfromNative tiv(JavaThread::current());
>> 1878 debug_only(VMNativeEntryWrapper vew;)
>>
>> shouldn't we already be _thread_in_vm at this point ??
>>
>
> I tried comment them out, and I get an abort. The thread state is
> "_thread_in_native". So it looks like we need this code to make the
> thread into _thread_in_vm so that we can enter the safe point??
>
>
> #0 0x0000003075430265 in raise () from /lib64/libc.so.6
> #1 0x0000003075431d10 in abort () from /lib64/libc.so.6
> #2 0x00002aaaab52cfdb in os::abort (dump_core=true) at
> /home/iklam/jdk/hsx24/src/os/linux/vm/os_linux.cpp:1584
> #3 0x00002aaaab6ded47 in VMError::report_and_die (this=0x400fe6c0) at
> /home/iklam/jdk/hsx24/src/share/vm/utilities/vmError.cpp:1026
> #4 0x00002aaaab1031ae in report_vm_error (file=0x2aaaab964e40
> "/home/iklam/jdk/hsx24/src/share/vm/runtime/thread.cpp", line=899,
> error_msg=0x2aaaab7f20af "fatal error", detail_msg=0x2aaaab968404
> "LEAF method calling lock?")
> at /home/iklam/jdk/hsx24/src/share/vm/utilities/debug.cpp:227
> #5 0x00002aaaab10402a in report_fatal (file=0x2aaaab964e40
> "/home/iklam/jdk/hsx24/src/share/vm/runtime/thread.cpp", line=899,
> message=0x2aaaab968404 "LEAF method calling lock?") at
> /home/iklam/jdk/hsx24/src/share/vm/utilities/debug.cpp:232
> #6 0x00002aaaab689187 in Thread::check_for_valid_safepoint_state
> (this=0x613800, potential_vm_operation=true)
> at /home/iklam/jdk/hsx24/src/share/vm/runtime/thread.cpp:899
> #7 0x00002aaaab70ccff in VMThread::execute (op=0x400feb60) at
> /home/iklam/jdk/hsx24/src/share/vm/runtime/vmThread.cpp:597
> #8 0x00002aaaab52b6ec in os::dll_load (filename=0x745240
> "/scratch/iklam/jdk/hsx24/test/runtime/JTwork/scratch/libtest-rwx.so",
> ebuf=0x400ff070 "\320\307j", ebuflen=1024) at
> /home/iklam/jdk/hsx24/src/os/linux/vm/os_linux.cpp:1898
> #9 0x00002aaaab368a3b in JVM_LoadLibrary (name=0x745240
> "/scratch/iklam/jdk/hsx24/test/runtime/JTwork/scratch/libtest-rwx.so")
> at /home/iklam/jdk/hsx24/src/share/vm/prims/jvm.cpp:3644
> #10 0x00002aaaac1ad92f in
> Java_java_lang_ClassLoader_00024NativeLibrary_load () from
> /scratch/iklam/jdk/official/jdk1.7.0_09/jre/lib/amd64/libjava.so
> #11 0x00002aaaac649b9b in ?? ()
> #12 0x00000000400ff6b0 in ?? ()
> #13 0x00002aaaac62c298 in ?? ()
> #14 0x00000000400ff660 in ?? ()
> #15 0x0000000000000000 in ?? ()
>
>
>>> 2. Using safepoint to modify stack guard is still not safe, since not
>>> all Java threads stop at safepoint. Have you thought about racing
>>> scenarios?
>>
>> There is no guaranteed fix for this problem, we can only do what we
>> can do. If a thread hits the Java guard pages while in native then I
>> think that causes an abort anyway. So if the guard is disabled we
>> just won't abort (a good thing?) but if we hit the pthread/libc guard
>> pages then we will abort anyway.
>>
>> David
>> -----
>>
>>> 3. typo - os_linux.cpp #1821 liner -> linker
>>>
>>> Thanks,
>>>
>>> -Zhengyu
>>>>
>>>> -------- Original Message --------
>>>> Subject: Re: RFR (S) JDK-7107135 - Stack guard pages becomes
>>>> writable
>>>> Date: Wed, 20 Feb 2013 10:40:39 -0800
>>>> From: Ioi Lam <ioi.lam at oracle.com>
>>>> To: hotspot-runtime-dev at openjdk.java.net
>>>>
>>>>
>>>>
>>>> [Moving the discussion tohotspot-runtime-dev at openjdk.java.net]
>>>>
>>>> The original request for review is cut-and-pasted atthe end of this
>>>> message.
>>>>
>>>> Thanks
>>>> - Ioi
>>>>
>>>>
>>>> On 02/20/2013 08:25 AM, Dean Long wrote:
>>>> > On 2/20/2013 3:01 AM, David Holmes wrote:
>>>> >> On 20/02/2013 6:32 PM, Dean Long wrote:
>>>> >>> On 2/20/2013 12:12 AM, David Holmes wrote:
>>>> >>>> On 20/02/2013 3:29 PM, Dean Long wrote:
>>>> >>>>> On 2/19/2013 6:48 PM, David Holmes wrote:
>>>> >>>>>> On 20/02/2013 11:39 AM, Dean Long wrote:
>>>> >>>>>>> On 2/19/2013 5:35 PM, David Holmes wrote:
>>>> >>>>>>>> On 20/02/2013 11:24 AM, Dean Long wrote:
>>>> >>>>>>>>>>
>>>> >>>>>>>>> If os::Linux::default_guard_size() returns non-zero, we
>>>> set an
>>>> >>>>>>>>> attribute
>>>> >>>>>>>>> for pthread_create telling it to create guard pages for us.
>>>> >>>>>>>>> These guard pages aren't set to rwx by the dynamic linker
>>>> because
>>>> >>>>>>>>> pthreads knows about them.
>>>> >>>>>>>>
>>>> >>>>>>>> Are you saying that these guard pages don't get reset when
>>>> the
>>>> >>>>>>>> library
>>>> >>>>>>>> is loaded (or that they will at least get repaired
>>>> afterwards) ?
>>>> >>>>>>>
>>>> >>>>>>> They will not be reset.
>>>> >>>>>>
>>>> >>>>>> Can you point me to any docs or the source code that
>>>> demonstrates
>>>> >>>>>> this? From previous discussions the OS only allowed you to
>>>> set page
>>>> >>>>>> bits not read them, and hence not add them. So I'd like to
>>>> see how
>>>> >>>>>> they are achieving this.
>>>> >>>>>>
>>>> >>>>>
>>>> >>>>> The magic happens here in change_stack_perm():
>>>> >>>>>
>>>> >>>>>http://sourceware.org/git/?p=glibc.git;a=blob;f=nptl/allocatestack.c#l314
>>>>
>>>> >>>>>
>>>> >>>>>
>>>> >>>>
>>>> >>>> But that simply makes the stack readable, writable and
>>>> executable but
>>>> >>>> skipping over the guard pages. The initial protection of the
>>>> guard
>>>> >>>> pages happens here:
>>>> >>>>
>>>> >>>> 634 if (mprotect (guard, guardsize, PROT_NONE) != 0)
>>>> >>>>
>>>> >>>> but I don't see anything in this code that prevents the guard
>>>> pages
>>>> >>>> from being modified when a library with executable stack is
>>>> loaded?
>>>> >>>>
>>>> >>>
>>>> >>> The code path that does the modifying looks like: dlopen -->
>>>> ... -->
>>>> >>> __make_stacks_executable --> change_stack_perm.
>>>> >>
>>>> >> Ah I see. The above is what causes the problem, but it skips the
>>>> >> built-in guard pages.
>>>> >>
>>>> >> I'm sure someone thought this made sense at some point. :( But it
>>>> >> sure seems like a bug to me.
>>>> >>
>>>> > Which part seems buggy, changing the permissions? It seems
>>>> necessary
>>>> > as long as executable stacks is
>>>> > a supported feature. It would be nice if dlopen() would just
>>>> fail to
>>>> > load these libraries based on some flag
>>>> > in the executable's ELF file. I think the existing flag means "no
>>>> > executable stacks used by this module",
>>>> > but "no executable stacks used by this process" would make more
>>>> sense
>>>> > for Java.
>>>> >
>>>> > dl
>>>> >
>>>> >> Thanks,
>>>> >> David
>>>> >>
>>>> >>>> Also note that for user supplied stack memory there are no
>>>> guard pages
>>>> >>>> added.
>>>> >>>>
>>>> >>> OK.
>>>> >>>
>>>> >>> dl
>>>> >>>
>>>> >>>> David
>>>> >>>> -----
>>>> >>>>
>>>> >>>>> I wish there was a way to change the guardsize after the
>>>> thread is
>>>> >>>>> created.
>>>> >>>>>
>>>> >>>>> dl
>>>> >>>>>
>>>> >>>
>>>> >
>>>>
>>>> Please review:
>>>> http://javaweb.us.oracle.com/~iklam/webrev/7107135/stack_guard_001/
>>>>
>>>> Bug: Stack guard pages are no more protected after loading a shared
>>>> library with executable stack
>>>> https://jbs.oracle.com/bugs/browse/JDK-7107135
>>>>
>>>> Background:
>>>>
>>>> Recent versions of Linux support Non-Executable Stack
>>>> protection -- by default, the stack is made non-executable to
>>>> prevent code injection via overflowing on-stack buffers.
>>>>
>>>> However, some old Linux DLLs require the stack to be
>>>> executable. For backwards compatibility, after loading such
>>>> DLLs, the Linux dynamic loader makes the stack executable.
>>>>
>>>> Due to a limitation of the Linux system call API, the Linux
>>>> dynamic loader makes the stack readable/writable as well. This
>>>> disables Java's stack guard.
>>>>
>>>> Summary of fix:
>>>>
>>>> 1. Check if DLL requires executable stack by inspecting ELF
>>>> header.
>>>> 2. Enter a Safepoint and load such DLLs in the VM thread.
>>>> - immediately after loading, change all Java stack guards
>>>> back to PROT_NONE.
>>>> 3. Leave Safepoint to resume Java execution.
>>>>
>>>> I also added a global flag LoadExecStackDllInVMThread to load
>>>> such "bad" DLLs outside of the safepoint (in case the DLL
>>>> invokes JNI functions inside static constructors, which are
>>>> executed before dlopen() returns).
>>>>
>>>> Note:
>>>>
>>>> I got this code from an outside contributor and I don't really
>>>> understand what this block does. Please comment if it's
>>>> correct:
>>>>
>>>> 1877: ThreadInVMfromNative tiv(JavaThread::current());
>>>> 1878: debug_only(VMNativeEntryWrapper vew;)
>>>>
>>>> Tests executed:
>>>>
>>>> * JPRT
>>>> * UTE (vm.quick.testlist)
>>>> * JTREG (hotspot/tests/runtime, hotspot/tests/closed/runtime)
>>>>
>>>> Thanks,
>>>> Ioi
>>>>
>>>>
>>>>
>>>>
>>>
>
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