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

[Peter Zijlstra]

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.