[resending because kernel.org seems to have mangled my SMTP credentials. I wonder if this is a common problem.] On Thu, May 11, 2017 at 4:44 PM, 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. > I like this. It wouldn't help the problem that I suspect is a major part of the motivation for this patch: a stack overflow could overwrite addr_limit. But we fixed that for real already. Slightly off-topic: I would *love* to see syscall_return_slowpath() or similar moved or at least mostly moved into generic code. Aside from the fact that it used to be written in asm, there's nothing fundamentally arch-specific about it. > > 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. It won't even slow them down that much. The slow path is reasonably fast these days. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
