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Subject: Re: [PATCH] hwmon: (dell-smm-hwmon) Disable BIOS fan control on
 SET_FAN
To:     =?UTF-8?Q?Pali_Roh=c3=a1r?= <pali.rohar@gmail.com>
Cc:     Guenter Roeck <linux@roeck-us.net>,
        Jean Delvare <jdelvare@suse.com>, linux-hwmon@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20191114211408.22123-1-gio@debian.org>
 <20191114213901.GA28532@roeck-us.net> <20191114215154.hze2avicv7pwiksp@pali>
 <7ea74678-59e4-2c23-6744-6d0b2eff0a67@debian.org>
 <20191115112902.yfaoqttsafmilijh@pali>
From:   Giovanni Mascellani <gio@debian.org>
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Organization: Debian
Message-ID: <97d17b37-0267-ae32-803c-ce8f7a871ab4@debian.org>
Date:   Fri, 15 Nov 2019 14:44:59 +0100
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Content-Type: multipart/mixed; boundary="ZyPZV5BvejC6SkRgRQ062JTBm8Pi9flLf";
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From: Giovanni Mascellani <gio@debian.org>
To: =?UTF-8?Q?Pali_Roh=c3=a1r?= <pali.rohar@gmail.com>
Cc: Guenter Roeck <linux@roeck-us.net>, Jean Delvare <jdelvare@suse.com>,
 linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org
Message-ID: <97d17b37-0267-ae32-803c-ce8f7a871ab4@debian.org>
Subject: Re: [PATCH] hwmon: (dell-smm-hwmon) Disable BIOS fan control on
 SET_FAN
References: <20191114211408.22123-1-gio@debian.org>
 <20191114213901.GA28532@roeck-us.net> <20191114215154.hze2avicv7pwiksp@pali>
 <7ea74678-59e4-2c23-6744-6d0b2eff0a67@debian.org>
 <20191115112902.yfaoqttsafmilijh@pali>
In-Reply-To: <20191115112902.yfaoqttsafmilijh@pali>

--ZyPZV5BvejC6SkRgRQ062JTBm8Pi9flLf
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: quoted-printable

Hi,

Il 15/11/19 12:29, Pali Roh=C3=A1r ha scritto:
> No. I have not tested that my patch on other models. You can look at
> that my patch link, some people already reported that on some models it=

> does not work...

Yes, I saw that. But they are also using other laptops, which could be
excluded by the whitelist until we have a working command for them.

> What is incompatible with Secure Boot? sys_iopl nor sys_ioperm has
> nothing to do with UEFI Secure Boot. They are just ordinary syscalls
> like any other and are executed on kernel side. And IIRC it is up to th=
e
> kernel how it set privileges for I/O ports. Maybe bootloaders under
> Secure Boot can set some other default values, but kernel can overwrite=

> them. I really do not see reason why it could be incompatible with UEFI=

> Secure Boot nor why it should not work. It just looks like improper
> setup from userspace.

Ah, my fault here: there is a patch to lock down the kernel when it is
started with Secure Boot[1], and I believed that was already in
mainline, but apparently it is not.

 [1]
https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/com=
mit?id=3D160a99536afc317b337212dd40eaba341702343e

> It makes sense to have implemented in kernel switching between automati=
c
> and manual mode as kernel has API for it. But it depends on the fact
> that we know which SMM API to call. And currently it is just some rando=
m
> call which we somehow observed that is working on 2 machines and on som=
e
> more other does not. Until we have fully working implementation we
> cannot put it into kernel.

Mmh, but then what is a plausible way forward to have this? Can't we
start populating a whitelist for the machines we already have a solution
for, and add more entries when they are discovered? This would already
give a benefit to the users of supported laptops, without impacting
users of unsupported laptops. My feeling is that if we pretend to have
information for all possible models supported by dell-smm-hwmon, we will
never benefit any user. Or can you suggest a plan?

> What does not make sense for me is to have that "protection" in kernel.=


I am not really sure which "protection" you mean. I didn't mean to
introduce any protection from userspace in my patch, I just wanted to
make SET_FAN working. I think that the kernel module cannot (and should
not) reliably protect itself from userspace sending random IO port
reads/writes.

Thanks, Giovanni.
--=20
Giovanni Mascellani <g.mascellani@gmail.com>
Postdoc researcher - Universit=C3=A9 Libre de Bruxelles


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