RFR(S): 8221175: Fix bad function case for controlled JVM crash on PPC64 big-endian

[Chris Phillips]

Hi

On 2019-03-22 12:15 p.m., Gustavo Romero wrote:
> Hi,
> 
> Please, could I get reviews for the following change?
> 
> bug   : https://bugs.openjdk.java.net/browse/JDK-8221175
> webrev: http://cr.openjdk.java.net/~gromero/8221175/v1/
> 
> It fixes the way a function pointer is defined in order to call a bad
> function
> at address 0xF (controlled crash case 13) on PPC64 big-endian machines.
> 
> On PPC64 big-endian compiler defaults to ABI ELFv1 which mandates function
> pointers to part of a function descriptor, at offset 0 [1].
> 
> Currently the SIGISEGV being generated by case 13 is incorrect because if a
> function descriptor is not use to call the bad function address the program
> segfaults before effectively calling the function, when trying to load
> the (bad) function pointer from offset 0 of base address 0xF, so before
> branching to the function.
> 
> It does not affect PPC64 little-endian machines because by default ABI
> ELFv2
> is used (instead of ABI ELFv1) and for that ABI no function descriptor is
> defined / employed.
> 
> The fix consists in defining properly a function descriptor with a bad
> function
> at offset 0 (the following offset are no important in that case) and
> using that
> function descriptor to call the bad function, only on PPC64 big-endian
> machines.
> 
> That issue was found when investigating the JDK-8220794 issue [2].
> 
> Thank you.
> 
> Best regards,
> Gustavo
> 
> [1]
> http://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi.html#FUNC-DES
> [2] https://bugs.openjdk.java.net/browse/JDK-8220794
> 
> 
> 
Looks good, but not a reviewer.

Chris