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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Mon, 03 Jun 2019 10:45:57 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH v1 2/2] s390x/tcg: Store only the necessary amount of doublewords for STFLE X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Thomas Huth , Ilya Leoshkevich , Andreas Krebbel , Cornelia Huck , qemu-s390x@nongnu.org, Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 03.06.19 12:38, Stefan Liebler wrote: > On 5/31/19 4:56 PM, David Hildenbrand wrote: >> The PoP (z14, 7-382) says: >> Doublewords to the right of the doubleword in which the >> highest-numbered facility bit is assigned for a model >> may or may not be stored. >> >> However, stack protection in certain binaries can't deal with that. >> "gzip" example code: >> >> f1b4: a7 08 00 03 lhi %r0,3 >> f1b8: b2 b0 f0 a0 stfle 160(%r15) >> f1bc: e3 20 f0 b2 00 90 llgc %r2,178(%r15) >> f1c2: c0 2b 00 00 00 01 nilf %r2,1 >> f1c8: b2 4f 00 10 ear %r1,%a0 >> f1cc: b9 14 00 22 lgfr %r2,%r2 >> f1d0: eb 11 00 20 00 0d sllg %r1,%r1,32 >> f1d6: b2 4f 00 11 ear %r1,%a1 >> f1da: d5 07 f0 b8 10 28 clc 184(8,%r15),40(%r1) >> f1e0: a7 74 00 06 jne f1ec >> f1e4: eb ef f1 30 00 04 lmg %r14,%r15,304(%r15) >> f1ea: 07 fe br %r14 >> f1ec: c0 e5 ff ff 9d 6e brasl %r14,2cc8 <__stack_chk_fai= l@plt> >> >> In QEMU, we currently have: >> max_bytes =3D 24 >> the code asks for (3 + 1) doublewords =3D=3D 32 bytes. >> >> If we write 32 bytes instead of only 24, and return "2 + 1" doubleword= s >> ("one less than the number of doulewords needed to contain all of the >> facility bits"), the example code detects a stack corruption. >> >> In my opinion, the code is wrong. However, it seems to work fine on >> real machines. So let's limit storing to the minimum of the requested >> and the maximum doublewords. > Hi David, >=20 > Thanks for catching this. I've reported the "gzip" example to Ilya and=20 > indeed, r0 is setup too large. He will fix it in gzip. >=20 > You've mentioned, that this is detected in certain binaries. > Can you please share those occurrences. Hi Stafan, thanks for your reply. I didn't track all occurrences, it *could* be that it was only gzip in the background making other processes fail. For example, the systemd "vitual console setup" unit failed, too, which was fixed by this change. I also remember, seeing segfaults in rpmbuild, for example. They only "changed" with this fix - I m still chasing different errors. :) You mentioned "He will fix it in gzip", so I assume this is a gzip issue and not a gcc/glibc/whatever toolchain issue? --=20 Thanks, David / dhildenb