On Wed, Jan 17, 2018 at 5:57 AM, Brian Gerst <brgerst@xxxxxxxxx> wrote: > On Wed, Jan 17, 2018 at 1:24 AM, Joerg Roedel <joro@xxxxxxxxxx> 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 <joro@xxxxxxxxxx> 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. But then again, you could take a fault on the trampoline stack if you get a bad segment. Perhaps just pushing the new stack pointer onto the process stack before user segment loads will be the right move. -- Brian Gerst -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
