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From: Borislav Petkov <bp@alien8.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: x86-ml <x86@kernel.org>, lkml <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] x86/msr: Filter MSR writes
Date: Fri, 12 Jun 2020 19:48:01 +0200	[thread overview]
Message-ID: <20200612174801.GE22660@zn.tnic> (raw)
In-Reply-To: <CAHk-=wjKr+eAdPg3q7S6N4Cwd1aMEOHc5qLaKE-wwhouZRo=uw@mail.gmail.com>

On Fri, Jun 12, 2020 at 10:20:03AM -0700, Linus Torvalds wrote:
> Since you already added the filtering, this looks fairly sane.
> 
> IOW, what MSR's do we expect people to maybe write to normally? You
> added MSR_IA32_ENERGY_PERF_BIAS as an allowed MST, maybe there are
> others?

Right, this MSR is being written by cpupower in tools/. My search was
confined within the kernel source only so there very likely are others.

If we want to add others, though, I think the criteria would be, if
writing to a MSR is safe - and this is where it becomes fuzzy but to use
the above example: if all it does is give hints to the hw but the hw can
ignore those hints and there's no other effect on the hw, then those
writes are fairly safe.

I'm pretty sure we'll massage that definition of "safe" over time.

> So I'm not against this, but I suspect the whitelist should be thought
> through more,

Yap.

> and then maybe the "allow_writes" parameter should be
> yes/no/default/<msr-list>, where "default" is that list of
> known-normal MSR's.

So I know of another out-of-tree tool which has a whole whitelist
management of MSRs: https://github.com/LLNL/msr-safe

Question is, what use cases we want to support. My thinking is to start
small and then keep extending it based on use cases we want to support.

> And I suspect it's a lot longer list than your single one. IIRC,
> people were working around CPU bugs or features by doing MSR writes at
> startup.
> 
> So the first phase might be to introduce this, but have the default
> for non-recognized MSR's be "log", not "deny".

Ok. How are we going to "learn" about those non-recognized MSRs? Ask
people to send us a note to lkml so that we can fix the list once they
see the logged message?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

  reply	other threads:[~2020-06-12 17:48 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-12 10:50 [RFC PATCH] x86/msr: Filter MSR writes Borislav Petkov
2020-06-12 16:34 ` Sean Christopherson
2020-06-12 16:46   ` Borislav Petkov
2020-06-12 16:57     ` Sean Christopherson
2020-06-12 17:03       ` Borislav Petkov
2020-06-12 17:43         ` Sean Christopherson
2020-06-12 17:52           ` Borislav Petkov
2020-06-12 17:20 ` Linus Torvalds
2020-06-12 17:48   ` Borislav Petkov [this message]
2020-06-12 19:47     ` Borislav Petkov
2020-06-12 20:39     ` Peter Zijlstra
2020-06-13  5:40       ` Tony Luck
2020-06-13  9:39       ` Borislav Petkov
2020-06-13 15:48 ` [PATCH -v2] " Borislav Petkov
2020-06-15  6:38   ` [PATCH -v2.1] " Borislav Petkov
2020-06-25  5:51     ` Sean Christopherson
2020-06-25  8:37       ` Borislav Petkov
2020-07-14 12:19     ` Chris Down
2020-07-14 15:47       ` Borislav Petkov
2020-07-14 16:04         ` Chris Down
2020-07-14 16:46           ` Luck, Tony
2020-07-14 16:58             ` Borislav Petkov
2020-07-14 17:02             ` Chris Down
2020-07-14 16:56           ` Borislav Petkov
2020-07-14 17:04             ` Chris Down
2020-07-14 18:52             ` Srinivas Pandruvada
2020-07-15  4:26               ` Borislav Petkov
2020-07-14 19:17           ` Matthew Garrett
2020-11-17 21:00             ` Mathieu Chouquet-Stringer
2020-11-17 21:20               ` Borislav Petkov
2020-11-18  8:58                 ` Mathieu Chouquet-Stringer
2020-11-18  9:09                 ` Mathieu Chouquet-Stringer
2020-11-18 11:50                   ` Borislav Petkov
2020-11-18 14:04                     ` [PATCH] " Mathieu Chouquet-Stringer
2020-11-18 17:50                       ` Borislav Petkov
2020-11-19 10:53                         ` Mathieu Chouquet-Stringer
2020-11-25 21:41                           ` Mathieu Chouquet-Stringer
2020-11-26 10:03                           ` Borislav Petkov
2020-11-17 21:21               ` [PATCH -v2.1] " Matthew Garrett
2020-11-17 21:22                 ` Matthew Garrett
2020-11-18  9:02                   ` Mathieu Chouquet-Stringer
2020-06-17 15:06 ` [tip: x86/misc] " tip-bot2 for Borislav Petkov
2020-06-25  8:45 ` tip-bot2 for Borislav Petkov

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