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.
Linus
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