Messages in this thread | | | Date | Sun, 10 Nov 2019 21:31:21 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [patch 7/9] x86/iopl: Restrict iopl() permission scope |
| |
On Sun, 10 Nov 2019, Andy Lutomirski wrote: > On 11/6/19 11:35 AM, Thomas Gleixner wrote: > > + > > + if (IS_ENABLED(CONFIG_X86_IOPL_EMULATION)) { > > + struct tss_struct *tss; > > + unsigned int tss_base; > > + > > + /* Prevent racing against a task switch */ > > + preempt_disable(); > > + tss = this_cpu_ptr(&cpu_tss_rw); > > + if (level == 3) { > > + /* Grant access to all I/O ports */ > > + set_thread_flag(TIF_IO_BITMAP); > > + tss_base = IO_BITMAP_OFFSET_VALID_ALL; > > Where is the actual TSS updated?
Here. It sets the offset to the all zero bitmap. That's all it needs.
> > + } else if (t->io_bitmap_ptr) { > > + /* Thread has a I/O bitmap */ > > + tss_update_io_bitmap(tss, t); > > + set_thread_flag(TIF_IO_BITMAP); > > + tss_base = IO_BITMAP_OFFSET_VALID_MAP; > > + } else { > > + /* Take it out of the context switch work burden */ > > + clear_thread_flag(TIF_IO_BITMAP); > > + tss_base = IO_BITMAP_OFFSET_INVALID; > > Ditto. > > I think what you need to do is have a single function, called by > exit_thread(), switch_to(), and here, that updates the TSS to match a > given task's IO bitmap state. This is probably switch_to_bitmap() or > similar.
Well, no. exit_thread() and this here actually fiddle with the TIF bit which is not what the switch to case does. There is some stuff which can be shared.
> (Maybe it already is, but I swear I checked all the patches in the > series and I can't find the body of tss_update_io_bitmap(). But you > should call it in all branches of this if-else thing.)
It's in that very same patch:
> -static void tss_update_io_bitmap(struct tss_struct *tss, > - struct thread_struct *thread) > +void tss_update_io_bitmap(struct tss_struct *tss, struct thread_struct *thread) > {
Let me try to get a bit more reuse. Which still leaves the TIF bit fiddling in this code path.
Thanks,
tglx
| |