Messages in this thread | | | From | Nadav Amit <> | Subject | Re: [patch 1/2] x86,module: Detect VMX modules and disable Split-Lock-Detect | Date | Fri, 3 Apr 2020 16:48:35 +0000 |
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> 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.
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