Messages in this thread | | | Date | Wed, 23 Nov 2016 15:29:17 -0200 | From | Henrique de Moraes Holschuh <> | Subject | Re: [PATCH v2] x86/mce: Include the PPIN in machine check records when it is available |
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On Wed, 23 Nov 2016, Borislav Petkov wrote: > On Wed, Nov 23, 2016 at 11:29:51AM -0200, Henrique de Moraes Holschuh wrote: > > 1. Assuming we can do it, always lock it when it is found to be unlocked > > at kernel boot. > > Because...?
Privacy, and the fact that /dev/cpu/msr exists and is enabled on almost all general-use distros.
> > 2. Not attempt to change its state from disabled to enabled *unless* > > given a command line parameter authorizing it. A kconfig-based > > solution for default+command line override would also work well IMHO, > > if it makes more sense. > > You can't reenable it:
Yeah, I just found the description for that thing in the IA32 manual.
It can be disabled + unlocked, disabled + locked, or enabled + unlocked. Once locked, it will stay disabled until the next reboot.
However, the manual makes it clear we are _not_ supposed to leave it enabled + unlocked. Apparently, we're supposed to do our business and disable+lock it (i.e. enable, read and store/process, disable+lock).
Looks like it is supposed to be used in a way that protects privacy by making it very hard for general use software to depend on it existing and being enabled.
-- Henrique Holschuh
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