On February 27, 2023 2:29:43 PM PST, Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> wrote: >When user shadow stack is use, Write=0,Dirty=1 is treated by the CPU as >shadow stack memory. So for shadow stack memory this bit combination is >valid, but when Dirty=1,Write=1 (conventionally writable) memory is being >write protected, the kernel has been taught to transition the Dirty=1 >bit to SavedDirty=1, to avoid inadvertently creating shadow stack >memory. It does this inside pte_wrprotect() because it knows the PTE is >not intended to be a writable shadow stack entry, it is supposed to be >write protected. > >However, when a PTE is created by a raw prot using mk_pte(), mk_pte() >can't know whether to adjust Dirty=1 to SavedDirty=1. It can't >distinguish between the caller intending to create a shadow stack PTE or >needing the SavedDirty shift. > >The kernel has been updated to not do this, and so Write=0,Dirty=1 >memory should only be created by the pte_mkfoo() helpers. Add a warning >to make sure no new mk_pte() start doing this. > >Tested-by: Pengfei Xu <pengfei.xu@xxxxxxxxx> >Tested-by: John Allen <john.allen@xxxxxxx> >Tested-by: Kees Cook <keescook@xxxxxxxxxxxx> >Acked-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx> >Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -- Kees Cook
