Re: [PATCH v2 0/6] x86/alternatives: text_poke() fixes

[Nadav Amit]

at 11:56 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> On Sun, Sep 02, 2018 at 10:32:18AM -0700, Nadav Amit wrote:
>> This patch-set addresses some issues that were raised in a recent
>> correspondence and might affect the security and the correctness of code
>> patching. (Note that patching performance is not addressed by this
>> patch-set).
>> 
>> The main issue that the patches deal with is the fact that the fixmap
>> PTEs that are used for patching are available for access from other
>> cores and might be exploited. They are not even flushed from the TLB in
>> remote cores, so the risk is even higher. Address this issue by
>> introducing a temporary mm that is only used during patching.
>> Unfortunately, due to init ordering, fixmap is still used during
>> boot-time patching. Future patches can eliminate the need for it.
> 
> Remind me; why are we doing it like this instead of fixing fixmap?
> Because while this fixes the text_poke crud, it does leave fixmap
> broken.

Do you have other fixmap mappings in mind that are modified after boot?