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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: x86-ml <x86@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	lkml <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] x86/msr: Filter MSR writes
Date: Fri, 12 Jun 2020 09:57:09 -0700	[thread overview]
Message-ID: <20200612165709.GB1026@linux.intel.com> (raw)
In-Reply-To: <20200612164602.GC22660@zn.tnic>

On Fri, Jun 12, 2020 at 06:46:02PM +0200, Borislav Petkov wrote:
> On Fri, Jun 12, 2020 at 09:34:06AM -0700, Sean Christopherson wrote:
> > The kernel should be tainted if the WRMSR is attempted, regardless of
> > whether it succeeds, and it should happen before the WRMSR.  E.g. pointing
> > MSR_IA32_DS_AREA at a bad address will likely cause an OOPS on the #PF
> 
> If the MSR write fails, MSR_IA32_DS_AREA won't have the bad address. If
> the writes fail, nothing has been changed.

DS_AREA takes a virtual (linear) address, i.e. the address can be legal from
the CPUs perspective but still lead to a #PF due to the address not being
mapped in the page tables.

> > This can be 0600, or maybe 0644, i.e. allow the user to enable/disable
> > writes after the module has been loaded.
> 
> What for?

So users don't have to unload and reload the module just to enable or
disable writes.  I don't think it changes the protections in any way, a
priveleged user still needs to explicitly toggle the control.

> crw------- 1 root root 202, 0 Jun 10 19:54 /dev/cpu/0/msr
> 
> You need root to write to the chrdev.
> 
> Also, the intent is *not* to open it more but to close it so that the
> incentive to design proper interfaces is there.
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

  reply	other threads:[~2020-06-12 16:57 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 [this message]
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
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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