On Fri, Dec 18, 2015 at 3:08 PM, Linus Torvalds <torva...@linux-foundation.org> wrote: > On Fri, Dec 18, 2015 at 2:28 PM, Andy Lutomirski <l...@amacapital.net> wrote: >> >> Apps that don't want to use the baseline_pkru mechanism could use >> syscalls to claim ownership of protection keys but then manage them >> purely with WRPKRU directly. We could optionally disallow >> mprotect_key on keys that weren't allocated in advance. >> >> Does that seem sane? > > So everything seems sane except for the need for that baseline_pkru. > > I'm not seeing why it couldn't just be a fixed value. Is there any > real downside to it?
Yes, I think. If I'm using protection keys to protect some critical data structure (important stuff in shared memory, important memory mapped files, pmem, etc), then I'll allocate a protection key and set PKRU to deny writes. The problem is that I really, really want writes denied except when explicitly enabled in narrow regions of code that use wrpkru to enable them, and I don't want an asynchronous signal delivered in those narrow regions of code or newly cloned threads to pick up the write-allow value. So I want baseline_pkru to have the deny writes entry. I think I would do exactly this in my production code here if my server supported it. Some day... Hrm. We might also want an option to change pkru and/or baseline_pkru in all threads in the current mm. That's optional but it could be handy. Maybe it would be as simple as having the allocate-a-pkey call have an option to set an initial baseline value and an option to propagate that initial value to pre-existing threads. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
