Messages in this thread | | | Date | Tue, 12 Nov 2019 18:10:56 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [patch V2 08/16] x86/ioperm: Add bitmap sequence number |
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On Tue, 12 Nov 2019, Andy Lutomirski wrote: > On Mon, Nov 11, 2019 at 2:35 PM Thomas Gleixner <tglx@linutronix.de> wrote: > > /* > > + * The bitmap pointer and the sequence number of the last active > > + * bitmap. last_bitmap cannot be dereferenced. It's solely for > > + * comparison. > > + */ > > + struct io_bitmap *last_bitmap; > > + u64 last_sequence; > > + > > + /* > > * Store the dirty size of the last io bitmap offender. The next > > * one will have to do the cleanup as the switch out to a non io > > * bitmap user will just set x86_tss.io_bitmap_base to a value > > Why is all this stuff in the TSS? Would it make more sense in a > percpu variable tss_state? By putting it in the TSS, you're putting > it in cpu_entry_area, which is at least a bit odd if not an actual > security problem. > > And why do you need a last_bitmap pointer? I thin that comparing just > last_sequence should be enough. Keeping last_bitmap around at all is > asking for trouble, since it might point to freed memory.
The bitmap pointer is pointless as I said in an earlier reply to Peter. It will go away. The sequence number and the dirty size are surely not a problem leakage wise, but yes, we could put it into a per cpu variable as well. Not sure whether it buys much.
> > - memcpy(tss->io_bitmap_bytes, iobm->bitmap_bytes, > > - max(tss->io_bitmap_prev_max, iobm->io_bitmap_max)); > > + if (tss->last_bitmap != iobm || > > + tss->last_sequence != iobm->sequence) > > As above, I think this could just be if (tss->last_sequence != > iobm->sequence) or even if (this_cpu_read(cpu_tss_state.iobm_sequence) > != iobm->sequence).
Already fixed as per Peter's comments.
Thanks,
tglx
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