On Wed, Jan 17, 2018 at 1:24 AM, Joerg Roedel <j...@8bytes.org> wrote: > On Tue, Jan 16, 2018 at 02:48:43PM -0800, Andy Lutomirski wrote: >> On Tue, Jan 16, 2018 at 8:36 AM, Joerg Roedel <j...@8bytes.org> wrote: >> > + /* Restore user %edi and user %fs */ >> > + movl (%edi), %edi >> > + popl %fs >> >> Yikes! We're not *supposed* to be able to observe an asynchronous >> descriptor table change, but if the LDT changes out from under you, >> this is going to blow up badly. It would be really nice if you could >> pull this off without percpu access or without needing to do this >> dance where you load user FS, then kernel FS, then user FS. If that's >> not doable, then you should at least add exception handling -- look at >> the other 'pop %fs' instructions in entry_32.S. > > You are right! This also means I need to do the 'popl %fs' before the > cr3-switch. I'll fix it in the next version. > > I have no real idea on how to switch back to the entry stack without > access to per_cpu variables. I also can't access the cpu_entry_area for > the cpu yet, because for that we need to be on the entry stack already.
Switch to the trampoline stack before loading user segments. -- Brian Gerst
