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Date: Mon, 21 Nov 2016 12:06:06 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Thomas Gleixner <tglx@...utronix.de> Cc: LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>, x86@...nel.org, Borislav Petkov <bp@...en8.de>, Yinghai Lu <yinghai@...nel.org> Subject: Re: [patch 4/8] x86/tsc: Verify TSC_ADJUST from idle On Mon, Nov 21, 2016 at 09:16:44AM +0100, Thomas Gleixner wrote: > On Sun, 20 Nov 2016, Peter Zijlstra wrote: > > On Sat, Nov 19, 2016 at 01:47:37PM -0000, Thomas Gleixner wrote: > > > When entering idle, it's a good oportunity to verify that the TSC_ADJUST > > > MSR has not been tampered with (BIOS hiding SMM cycles). If tampering is > > > detected, emit a warning and restore it to the previous value. > > > > > +++ b/arch/x86/kernel/process.c > > > @@ -277,6 +277,7 @@ void exit_idle(void) > > > > > > void arch_cpu_idle_enter(void) > > > { > > > + tsc_verify_tsc_adjust(); > > > local_touch_nmi(); > > > enter_idle(); > > > } > > > > Doing a RDMSR on the idle path isn't going to be popular. That path is > > already way too slow. > > Of course we can ratelimit that MSR read with jiffies, but do you have any > better suggestion aside of doing it timer based? Not really :/
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