Messages in this thread | | | Date | Fri, 3 Apr 2020 10:21:29 -0700 | From | Sean Christopherson <> | Subject | Re: [patch 1/2] x86,module: Detect VMX modules and disable Split-Lock-Detect |
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On Fri, Apr 03, 2020 at 04:48:35PM +0000, Nadav Amit wrote: > > On Apr 3, 2020, at 9:40 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > > > On Fri, Apr 03, 2020 at 09:25:55AM -0700, Sean Christopherson wrote: > >> On Fri, Apr 03, 2020 at 06:12:05PM +0200, Peter Zijlstra wrote: > >>> On Fri, Apr 03, 2020 at 09:01:56AM -0700, Sean Christopherson wrote: > >>>> On Fri, Apr 03, 2020 at 05:21:58PM +0200, Peter Zijlstra wrote: > >>>>> On Fri, Apr 03, 2020 at 04:35:00PM +0200, Jessica Yu wrote: > >>> > >>>>>> I wonder if it would make sense then to limit the text scans to just > >>>>>> out-of-tree modules (i.e., missing the intree modinfo flag)? > >>>>> > >>>>> It would; didn't know there was one. > >>>> > >>>> Rather than scanning modules at all, what about hooking native_write_cr4() > >>>> to kill SLD if CR4.VMXE is toggled on and the caller didn't increment a > >>>> "sld safe" counter? > >>> > >>> And then you're hoping that the module uses that and not: > >>> > >>> asm volatile ("mov %0, cr4" :: "r" (val)); > >>> > >>> I think I feel safer with the scanning to be fair. Also with the intree > >>> hint on, we can extend the scanning for out-of-tree modules for more > >>> dodgy crap we really don't want modules to do, like for example the > >>> above. > >> > >> Ya, that's the big uknown. But wouldn't they'd already be broken in the > >> sense that they'd corrupt the CR4 shadow? E.g. setting VMXE without > >> updating cpu_tlbstate.cr4 would result in future in-kernel writes to CR4 > >> attempting to clear CR4.VMXE post-VMXON, which would #GP. > > > > Sadly the CR4 shadow is exported, so they can actually fix that up :/ > > I do not think that Sean’s idea would work for VMware.
Well phooey.
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