Recent Intel x64 CPUs support a new security feature called CET (Control-flow Enforcement Technology). We plan to support it in the .NET 6.0.

Windows and Linux

• Add Shadow stack popping during stack unwinding.

Windows

• Add proper compiler and linker options to support CET for the C/C++ code.
• Implement our own version of RtlRestoreContext for exception handling (done on Windows only for now)
• Implement new way of thread suspension using a new user mode APC that would work the same way as on Unix.
• Implement new way of return address hijacking compatible with the CET.
• Make ThreadAbort work with CET enabled
• Make GC stress 4/8 work with CET enabled
• Enable CI for CET
• Enable non-strict mode by default
• Performance is comparable without CET enabled
• Debugging support is not restricted with CET enabled

Linux

• Add proper compiler options to enable IBT (indirect branch tracing) support and .note.gnu.property section to indicate our native runtime binaries are compatible with shadow stack and IBT.
• Add ENDBR instructions at the beginning of asm helper functions that can be called using indirect jumps or calls.
• Modify JIT to add ENDBR instructions at the beginning of all methods that can be called via indirect jumps or calls.
• The Linux work depends on the availability of the CET support in the mainstream Linux kernel. There is a patch that adds some arch_prctl operations for the Intel CET.