On Mon, 24 Jan 2022 15:56:06 GMT, Alan Hayward <d...@openjdk.java.net> wrote:
>> PAC is an optional feature in AArch64 8.3 and is compulsory in v9. One >> of its uses is to protect against ROP based attacks. This is done by >> signing the Link Register whenever it is stored on the stack, and >> authenticating the value when it is loaded back from the stack. If an >> attacker were to try to change control flow by editing the stack then >> the authentication check of the Link Register will fail, causing a >> segfault when the function returns. >> >> On a system with PAC enabled, it is expected that all applications will >> be compiled with ROP protection. Fedora 33 and upwards already provide >> this. By compiling for ARMv8.0, GCC and LLVM will only use the set of >> PAC instructions that exist in the NOP space - on hardware without PAC, >> these instructions act as NOPs, allowing backward compatibility for >> negligible performance cost (2 NOPs per non-leaf function). >> >> Hardware is currently limited to the Apple M1 MacBooks. All testing has >> been done within a Fedora Docker image. A run of SpecJVM showed no >> difference to that of noise - which was surprising. >> >> The most important part of this patch is simply compiling using branch >> protection provided by GCC/LLVM. This protects all C++ code from being >> used in ROP attacks, removing all static ROP gadgets from use. >> >> The remainder of the patch adds ROP protection to runtime generated >> code, in both stubs and compiled Java code. Attacks here are much harder >> as ROP gadgets must be found dynamically at runtime. If/when AOT >> compilation is added to JDK, then all stubs and compiled Java will be >> susceptible ROP gadgets being found by static analysis and therefore >> potentially as vulnerable as C++ code. >> >> There are a number of places where the VM changes control flow by >> rewriting the stack or otherwise. I’ve done some analysis as to how >> these could also be used for attacks (which I didn’t want to post here). >> These areas can be protected ensuring the pointers to various stubs and >> entry points are stored in memory as signed pointers. These changes are >> simple to make (they can be reduced to a type change in common code and >> a few addition sign/auth calls in the backend), but there a lot of them >> and the total code change is fairly large. I’m happy to provide a few >> work in progress patches. >> >> In order to match the security benefits of the Apple Arm64e ABI across >> the whole of JDK, then all the changes mentioned above would be >> required. > > Alan Hayward has updated the pull request incrementally with one additional > commit since the last revision: > > Fix popframe failures I've reverted my approval pending my question which wasn't resolved. ------------- Changes requested by aph (Reviewer). PR: https://git.openjdk.java.net/jdk/pull/6334
