Messages in this thread |  | | Date | Tue, 24 Feb 2015 22:23:54 -0500 | Subject | Re: [PATCH 3.2 055/152] x86_64, switch_to(): Load TLS descriptors before switching DS and ES | From | Brian Gerst <> |
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On Tue, Feb 24, 2015 at 3:08 PM, Denys Vlasenko <vda.linux@googlemail.com> wrote: > On Tue, Feb 24, 2015 at 9:02 PM, Andy Lutomirski <luto@amacapital.net> wrote: >>> This currently fails in 32-bit kernels (at least in qemu): >>> >>> / # ./es_test >>> Allocated GDT index 7 >>> [FAIL] ES changed from 0x3b to 0x7b >>> [FAIL] ES was corrupted 1000/1000 times >>> / # uname -a >>> Linux (none) 4.0.0-rc1 #1 SMP Tue Feb 24 16:41:58 CET 2015 i686 GNU/Linux >> >> Want to send a patch? I'll get it in a few days if no one beats me. > > I have no patch, sorry (in fact, I failed to find where is the relevant > 32-bit counterpart). > > It's just security people asked me to backport this and I wondered > maybe I should wait a bit on this one, since fix for 32-bit ought > to appear as well.
For 32-bit kernel, userspace DS and ES are saved at syscall/interrupt entry time and reloaded on exit, unlike in 64-bit where they are saved and loaded at context switch time. Therefore 32-bit is not affected by the issue this patch addresses.
It looks to me though, that the ES test program doesn't actually test what the patch fixes - the segment attributes, like the base address. It tests just the selector, which shouldn't change across a kernel entry (with a few exceptions, like signals). If the test is failing, then it is a different issue from what this patch addresses.
-- Brian Gerst
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