Messages in this thread | | | Date | Wed, 17 Jan 2018 10:24:42 +0100 | From | Joerg Roedel <> | Subject | Re: [PATCH 03/16] x86/entry/32: Leave the kernel via the trampoline stack |
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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@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.
Joerg
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