linux-kernel - Re: [PATCH v3] x86/mce: retrieve poison range from hardware

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Date:   Mon, 18 Jul 2022 14:37:53 -0700
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Jane Chu <jane.chu@...cle.com>
Cc:     "Williams, Dan J" <dan.j.williams@...el.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hch@....de" <hch@....de>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>
Subject: Re: [PATCH v3] x86/mce: retrieve poison range from hardware

On Mon, Jul 18, 2022 at 09:11:33PM +0000, Jane Chu wrote:
> On 7/18/2022 12:22 PM, Luck, Tony wrote:
> >> It appears the kernel is trusting that ->physical_addr_mask is non-zero
> >> in other paths. So this is at least equally broken in the presence of a
> >> broken BIOS. The impact is potentially larger though with this change,
> >> so it might be a good follow-on patch to make sure that
> >> ->physical_addr_mask gets fixed up to a minimum mask value.
> > 
> > Agreed. Separate patch to sanitize early, so other kernel code can just use it.
> > 
> 
> Is it possible that with
>    if (mem->validation_bits & CPER_MEM_VALID_PA_MASK)
> the ->physical_addr_mask is still untrustworthy?

The validation_bits just show which fields the BIOS *says* it filled in.
If a validation bit isn't set, then Linux should certainly ignore that
field. But if it is set, then Linux needs to decide whether to use the
value, or do a sanity check first.

-Tony