[ruby-core:105741] [Ruby master Bug#18260] YJIT uses insecure mmap protections
From:
"maximecb (Maxime Chevalier-Boisvert)" <noreply@...>
Date:
2021-10-21 20:34:48 UTC
List:
ruby-core #105741
Issue #18260 has been updated by maximecb (Maxime Chevalier-Boisvert). We can look into this. The downside is that YJIT does a lot of code patching, so this would presumably involve two system calls every time YJIT needs to generate code. Hopefully the performance impact will be relatively minimal. ---------------------------------------- Bug #18260: YJIT uses insecure mmap protections https://bugs.ruby-lang.org/issues/18260#change-94242 * Author: jeremyevans0 (Jeremy Evans) * Status: Open * Priority: Normal * Assignee: maximecb (Maxime Chevalier-Boisvert) * Backport: 2.6: DONTNEED, 2.7: DONTNEED, 3.0: DONTNEED ---------------------------------------- YJIT uses `mmap` with `PROT_READ | PROT_WRITE | PROT_EXEC` protections, which reduces security because it makes code injection attacks much easier, as the attacker only needs to be able to write their shellcode to the mapped memory region and then directly jump to the shellcode just written. The security principle being violated here is referred to as `W^X` (W xor X). Basically, memory can be either writable or executable, but never both at the same. OpenBSD has disallowed `mmap` with `PROT_WRITE | PROT_EXEC` by default since 2016. NetBSD/Linux with PaX MPROTECT disallows this as well, as does SELinux unless you enable `allow_execmem`. Fixing this generally involves initially mapping pages with `PROT_READ | PROT_WRITE`, and after writing executable code, using `mprotect` to switch to `PROT_READ | PROT_EXEC`. This is the approach that Firefox takes for their Javascript engine starting in Firefox 46. This makes code injection attacks more difficult as an attacker either cannot write the shellcode (if mapped `PROT_READ | PROT_EXEC`), or cannot jump directly to the shellcode after writing (if mapped `PROT_READ | PROT_WRITE`). -- https://bugs.ruby-lang.org/ Unsubscribe: <mailto:ruby-core-request@ruby-lang.org?subject=unsubscribe> <http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>