Re: [PATCH 3/3] x86/MCE/AMD: Get address from already initialized block

Johannes Hirte
2018-05-17T06:49:42Z

On 2018 Mai 17, Borislav Petkov wrote:
> On Tue, May 15, 2018 at 11:39:54AM +0200, Johannes Hirte wrote:
> > The out-of-bound access happens in get_block_address:
> >
> > if (bankp && bankp->blocks) {
> > struct threshold_block *blockp blockp = &bankp->blocks[block];
> >
> > with block=1. This doesn't exists. I don't even find any array here.
> > There is a linked list, created in allocate_threshold_blocks. On my
> > system I get 17 lists with one element each.
>
> Yes, what a mess this is. ;-\
>
> There's no such thing as ->blocks[block] array. We assign simply the
> threshold_block to it in allocate_threshold_blocks:
>
> per_cpu(threshold_banks, cpu)[bank]->blocks = b;
>
> And I can't say the design of this thing is really friendly but it is
> still no excuse that I missed that during review. Grrr.
>
> So, Yazen, what really needs to happen here is to iterate the
> bank->blocks->miscj list to find the block you're looking for and return
> its address, the opposite to this here:
>
> if (per_cpu(threshold_banks, cpu)[bank]->blocks) {
> list_add(&b->miscj,
> &per_cpu(threshold_banks, cpu)[bank]->blocks->miscj);
> } else {
> per_cpu(threshold_banks, cpu)[bank]->blocks = b;
> }
>
> and don't forget to look at ->blocks itself.
>
> And then you need to make sure that searching for block addresses still
> works when resuming from suspend so that you can avoid the RDMSR IPIs.
>

Maybe I'm missing something, but those RDMSR IPSs don't happen on
pre-SMCA systems, right? So the caching should be avoided here, cause
the whole lookup looks more expensive to me than the simple switch-block
in get_block_address.

--
Regards,
Johannes