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?
