Messages in this thread | | | Date | Fri, 12 Jun 2020 19:52:51 +0200 | From | Borislav Petkov <> | Subject | Re: [RFC PATCH] x86/msr: Filter MSR writes |
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On Fri, Jun 12, 2020 at 10:43:07AM -0700, Sean Christopherson wrote: > The problem is a fault on WRMSR doesn't mean the MSR doesn't exist, it only > means WRMSR faulted. WRMSR can for all intents and purpose trigger completely > arbitrary microcode flows, e.g. WRMSR 0x79 can fundamentally change the > behavior of the CPU.
Yes, that case is in the commit message.
> And it's not like the WRMSR->taint is atomic, e.g. changing a platform scoped > MSR that affects voltage settings or something of that nature could easily > tank the system on a successful WRMSR before the kernel can be marked tainted.
Yes, yes, I'll taint before the WRMSR.
> 0400 only allows a privelged user to read the parameter, e.g. for parameters > that are snapshotted at module load time and/or changing the param while the > module is running would cause breakage. > > 0600 allows a priveleged user to read and write the parameter, which AFAICT > is safe here.
Ok, we can do that.
> 0644 allows a priveleged user to read and write the parameter, and allows an > unpriveleged user to read the param.
Not so sure about that. Why would the unprivileged user need to read it?
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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