On Thu, 11 May 2017 16:44:07 -0700 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Thu, May 11, 2017 at 4:17 PM, Thomas Garnier <thgarnie@xxxxxxxxxx> wrote: > > > > Ingo: Do you want the change as-is? Would you like it to be optional? > > What do you think? > > I'm not ingo, but I don't like that patch. It's in the wrong place - > that system call return code is too timing-critical to add address > limit checks. > > Now what I think you *could* do is: > > - make "set_fs()" actually set a work flag in the current thread flags > > - do the test in the slow-path (syscall_return_slowpath). > > Yes, yes, that ends up being architecture-specific, but it's fairly simple. > > And it only slows down the system calls that actually use "set_fs()". > Sure, it will slow those down a fair amount, but they are hopefully a > small subset of all cases. > > How does that sound to people? Thats' where we currently do that > > if (IS_ENABLED(CONFIG_PROVE_LOCKING) && > WARN(irqs_disabled(), "syscall %ld left IRQs disabled", > regs->orig_ax)) > local_irq_enable(); > > check too, which is a fairly similar issue. This is exactly what Heiko did for the s390 backend as a result of this discussion. See the _CIF_ASCE_SECONDARY bit in arch/s390/kernel/entry.S, for the hot patch the check for the bit is included in the general _CIF_WORK test. Only the slow patch gets a bit slower. git commit b5a882fcf146c87cb6b67c6df353e1c042b8773d "s390: restore address space when returning to user space". -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
