On Tue, Feb 24, 2015 at 7:23 PM, Brian Gerst <brgerst@xxxxxxxxx> wrote: > On Tue, Feb 24, 2015 at 3:08 PM, Denys Vlasenko > <vda.linux@xxxxxxxxxxxxxx> wrote: >> On Tue, Feb 24, 2015 at 9:02 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> 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. It tests it indirectly. The 64-bit code sets the selector to zero if it fails to reload it. Testing the ES base is awkward because it can't be done in 64-bit code at all. --Andy -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html