linux-kernel - RE: [PATCH v2 12/14] platform/x86/intel/ifs: Add current

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Date:   Mon, 14 Nov 2022 18:25:28 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     "Hansen, Dave" <dave.hansen@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        "Raj, Ashok" <ashok.raj@...el.com>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "Macieira, Thiago" <thiago.macieira@...el.com>,
        "Joseph, Jithu" <jithu.joseph@...el.com>,
        "hdegoede@...hat.com" <hdegoede@...hat.com>,
        "markgross@...nel.org" <markgross@...nel.org>,
        "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>, "hpa@...or.com" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "Jimenez Gonzalez, Athenas" <athenas.jimenez.gonzalez@...el.com>,
        "Mehta, Sohil" <sohil.mehta@...el.com>
Subject: RE: [PATCH v2 12/14] platform/x86/intel/ifs: Add current_batch sysfs
 entry

> So, what's the point of the sscanf() to check the *filename* other than
> saving some potentially expensive request_firmware() calls?

Not much point. There are two subsequent checks.  First the driver checks
the F-M-S in the header of the file ... so your dastardly user will be thwarted
by this check.

If an even more dastardly user edited the file to have the right F-M-S (and
recomputed the file checksum) then the driver would be fooled, but microcode
would see that the signed binary portion is not for this CPU and reject it.

-Tony