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

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Date:   Mon, 18 Jul 2022 21:11:33 +0000
From:   Jane Chu <jane.chu@...cle.com>
To:     "Luck, Tony" <tony.luck@...el.com>,
        "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 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?

include/ras/ras_event.h has this
       if (mem->validation_bits & CPER_MEM_VALID_PA_MASK)
                         __entry->pa_mask_lsb = 
(u8)__ffs64(mem->physical_addr_mask);
                 else
                         __entry->pa_mask_lsb = ~0;
which hints otherwise.

apei_mce_report_mem_error() already checks mem->validation_bits
up front.

thanks!
-jane


> -Tony