| Message ID | 20190410123258.37f182cf@mschwideX1 |
|---|---|
| State | Not applicable |
| Headers |
Received: (qmail 47741 invoked by alias); 10 Apr 2019 10:33:09 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: <libc-alpha.sourceware.org> List-Unsubscribe: <mailto:libc-alpha-unsubscribe-##L=##H@sourceware.org> List-Subscribe: <mailto:libc-alpha-subscribe@sourceware.org> List-Archive: <http://sourceware.org/ml/libc-alpha/> List-Post: <mailto:libc-alpha@sourceware.org> List-Help: <mailto:libc-alpha-help@sourceware.org>, <http://sourceware.org/ml/#faqs> Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 47444 invoked by uid 89); 10 Apr 2019 10:33:08 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-13.9 required=5.0 tests=AWL, BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, KHOP_DYNAMIC, RCVD_IN_DNSWL_LOW, SPF_PASS autolearn=ham version=3.3.1 spammy=MIT, HX-Languages-Length:3109, reality X-HELO: mx0a-001b2d01.pphosted.com Date: Wed, 10 Apr 2019 12:32:58 +0200 From: Martin Schwidefsky <schwidefsky@de.ibm.com> To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: heiko carstens <heiko.carstens@de.ibm.com>, gor <gor@linux.ibm.com>, libc-alpha <libc-alpha@sourceware.org>, linux-kernel <linux-kernel@vger.kernel.org>, "Carlos O'Donell" <carlos@redhat.com> Subject: Re: rseq/s390: choosing code signature In-Reply-To: <1779981820.2626.1554838342731.JavaMail.zimbra@efficios.com> References: <1779981820.2626.1554838342731.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit x-cbid: 19041010-0028-0000-0000-0000035F450D X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19041010-0029-0000-0000-0000241E66E3 Message-Id: <20190410123258.37f182cf@mschwideX1> |
Commit Message
Martin Schwidefsky
April 10, 2019, 10:32 a.m. UTC
On Tue, 9 Apr 2019 15:32:22 -0400 (EDT) Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > Hi, > > We are about to include the code signature required prior to restartable > sequences abort handlers into glibc, which will make this ABI choice final. > We need architecture maintainer input on that signature value. > > That code signature is placed before each abort handler, so the kernel can > validate that it is indeed jumping to an abort handler (and not some > arbitrary attacker-chosen code). The signature is never executed. > > The current discussion thread on the glibc mailing list leads us towards > using a trap with uncommon immediate operand, which simplifies integration > with disassemblers, emulators, makes it easier to debug if the control > flow gets redirected there by mistake, and is nicer for some architecture's > speculative execution. > > We can have different signatures for each sub-architecture, as long as they > don't have to co-exist within the same process. We can special-case with > #ifdef for each sub-architecture and endianness if need be. If the architecture > has instruction set extensions that can co-exist with the architecture > instruction set within the same process, we need to take into account to which > instruction the chosen signature value would map (and possibly decide if we > need to extend rseq to support many signatures). > > Here is an example of rseq signature definition template: > > /* > * TODO: document trap instruction objdump output on each sub-architecture > * instruction sets, as well as instruction set extensions. > */ > #define RSEQ_SIG 0x######## > > Ideally we'd need a patch on top of the Linux kernel > tools/testing/selftests/rseq/rseq-s390.h file that updates > the signature value, so I can then pick it up for the glibc > patchset. The trap4 instruction is a suitable one. The patch would look like this -- commit 2ee28f6d1de968a71f074ab150384b90b4121216 Author: Martin Schwidefsky <schwidefsky@de.ibm.com> Date: Wed Apr 10 12:28:41 2019 +0200 s390/rseq: use trap4 for RSEQ_SIG Use trap4 as the guard instruction for the restartable sequence abort handler. Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Comments
----- On Apr 10, 2019, at 6:32 AM, schwidefsky schwidefsky@de.ibm.com wrote: > On Tue, 9 Apr 2019 15:32:22 -0400 (EDT) > Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > >> Hi, >> >> We are about to include the code signature required prior to restartable >> sequences abort handlers into glibc, which will make this ABI choice final. >> We need architecture maintainer input on that signature value. >> >> That code signature is placed before each abort handler, so the kernel can >> validate that it is indeed jumping to an abort handler (and not some >> arbitrary attacker-chosen code). The signature is never executed. >> >> The current discussion thread on the glibc mailing list leads us towards >> using a trap with uncommon immediate operand, which simplifies integration >> with disassemblers, emulators, makes it easier to debug if the control >> flow gets redirected there by mistake, and is nicer for some architecture's >> speculative execution. >> >> We can have different signatures for each sub-architecture, as long as they >> don't have to co-exist within the same process. We can special-case with >> #ifdef for each sub-architecture and endianness if need be. If the architecture >> has instruction set extensions that can co-exist with the architecture >> instruction set within the same process, we need to take into account to which >> instruction the chosen signature value would map (and possibly decide if we >> need to extend rseq to support many signatures). >> >> Here is an example of rseq signature definition template: >> >> /* >> * TODO: document trap instruction objdump output on each sub-architecture >> * instruction sets, as well as instruction set extensions. >> */ >> #define RSEQ_SIG 0x######## >> >> Ideally we'd need a patch on top of the Linux kernel >> tools/testing/selftests/rseq/rseq-s390.h file that updates >> the signature value, so I can then pick it up for the glibc >> patchset. > > The trap4 instruction is a suitable one. The patch would look like this Great! I'm picking it up into my rseq tree if that's OK with you. Thanks, Mathieu > -- > commit 2ee28f6d1de968a71f074ab150384b90b4121216 > Author: Martin Schwidefsky <schwidefsky@de.ibm.com> > Date: Wed Apr 10 12:28:41 2019 +0200 > > s390/rseq: use trap4 for RSEQ_SIG > > Use trap4 as the guard instruction for the restartable sequence abort > handler. > > Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> > > diff --git a/tools/testing/selftests/rseq/rseq-s390.h > b/tools/testing/selftests/rseq/rseq-s390.h > index 1069e85258ce..d4c8e1147d86 100644 > --- a/tools/testing/selftests/rseq/rseq-s390.h > +++ b/tools/testing/selftests/rseq/rseq-s390.h > @@ -1,6 +1,13 @@ > /* SPDX-License-Identifier: LGPL-2.1 OR MIT */ > > -#define RSEQ_SIG 0x53053053 > +/* > + * RSEQ_SIG uses the trap4 instruction. As Linux does not make use of the > + * access-register mode nor the linkage stack this instruction will always > + * cause a special-operation exception (the trap-enabled bit in the DUCT > + * is and will stay 0). The instruction pattern is > + * b2 ff 0f ff trap4 4095(%r0) > + */ > +#define RSEQ_SIG 0xB2FF0FFF > > #define rseq_smp_mb() __asm__ __volatile__ ("bcr 15,0" ::: "memory") > #define rseq_smp_rmb() rseq_smp_mb() > -- > blue skies, > Martin. > > "Reality continues to ruin my life." - Calvin.
On Wed, 10 Apr 2019 11:50:39 -0400 (EDT) Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > ----- On Apr 10, 2019, at 6:32 AM, schwidefsky schwidefsky@de.ibm.com wrote: > > > On Tue, 9 Apr 2019 15:32:22 -0400 (EDT) > > Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > > > >> Hi, > >> > >> We are about to include the code signature required prior to restartable > >> sequences abort handlers into glibc, which will make this ABI choice final. > >> We need architecture maintainer input on that signature value. > >> > >> That code signature is placed before each abort handler, so the kernel can > >> validate that it is indeed jumping to an abort handler (and not some > >> arbitrary attacker-chosen code). The signature is never executed. > >> > >> The current discussion thread on the glibc mailing list leads us towards > >> using a trap with uncommon immediate operand, which simplifies integration > >> with disassemblers, emulators, makes it easier to debug if the control > >> flow gets redirected there by mistake, and is nicer for some architecture's > >> speculative execution. > >> > >> We can have different signatures for each sub-architecture, as long as they > >> don't have to co-exist within the same process. We can special-case with > >> #ifdef for each sub-architecture and endianness if need be. If the architecture > >> has instruction set extensions that can co-exist with the architecture > >> instruction set within the same process, we need to take into account to which > >> instruction the chosen signature value would map (and possibly decide if we > >> need to extend rseq to support many signatures). > >> > >> Here is an example of rseq signature definition template: > >> > >> /* > >> * TODO: document trap instruction objdump output on each sub-architecture > >> * instruction sets, as well as instruction set extensions. > >> */ > >> #define RSEQ_SIG 0x######## > >> > >> Ideally we'd need a patch on top of the Linux kernel > >> tools/testing/selftests/rseq/rseq-s390.h file that updates > >> the signature value, so I can then pick it up for the glibc > >> patchset. > > > > The trap4 instruction is a suitable one. The patch would look like this > > Great! I'm picking it up into my rseq tree if that's OK with you. Just added the patch to s390/linux:features for the next merge window as well.
----- On Apr 10, 2019, at 11:52 AM, schwidefsky schwidefsky@de.ibm.com wrote: > On Wed, 10 Apr 2019 11:50:39 -0400 (EDT) > Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > >> ----- On Apr 10, 2019, at 6:32 AM, schwidefsky schwidefsky@de.ibm.com wrote: >> >> > On Tue, 9 Apr 2019 15:32:22 -0400 (EDT) >> > Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: >> > >> >> Hi, >> >> >> >> We are about to include the code signature required prior to restartable >> >> sequences abort handlers into glibc, which will make this ABI choice final. >> >> We need architecture maintainer input on that signature value. >> >> >> >> That code signature is placed before each abort handler, so the kernel can >> >> validate that it is indeed jumping to an abort handler (and not some >> >> arbitrary attacker-chosen code). The signature is never executed. >> >> >> >> The current discussion thread on the glibc mailing list leads us towards >> >> using a trap with uncommon immediate operand, which simplifies integration >> >> with disassemblers, emulators, makes it easier to debug if the control >> >> flow gets redirected there by mistake, and is nicer for some architecture's >> >> speculative execution. >> >> >> >> We can have different signatures for each sub-architecture, as long as they >> >> don't have to co-exist within the same process. We can special-case with >> >> #ifdef for each sub-architecture and endianness if need be. If the architecture >> >> has instruction set extensions that can co-exist with the architecture >> >> instruction set within the same process, we need to take into account to which >> >> instruction the chosen signature value would map (and possibly decide if we >> >> need to extend rseq to support many signatures). >> >> >> >> Here is an example of rseq signature definition template: >> >> >> >> /* >> >> * TODO: document trap instruction objdump output on each sub-architecture >> >> * instruction sets, as well as instruction set extensions. >> >> */ >> >> #define RSEQ_SIG 0x######## >> >> >> >> Ideally we'd need a patch on top of the Linux kernel >> >> tools/testing/selftests/rseq/rseq-s390.h file that updates >> >> the signature value, so I can then pick it up for the glibc >> >> patchset. >> > >> > The trap4 instruction is a suitable one. The patch would look like this >> >> Great! I'm picking it up into my rseq tree if that's OK with you. > > Just added the patch to s390/linux:features for the next merge window as well. Sounds good! I'll carry it in my tree to have a comprehensive up-to-date list of rseq signatures for all architectures in a single tree. Worse-case the exact same change will be pulled from both architecture and rseq trees, which I don't think should be an issue, right ? Thanks, Mathieu > > -- > blue skies, > Martin. > > "Reality continues to ruin my life." - Calvin.
On Wed, 10 Apr 2019 11:57:36 -0400 (EDT) Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > ----- On Apr 10, 2019, at 11:52 AM, schwidefsky schwidefsky@de.ibm.com wrote: > > > On Wed, 10 Apr 2019 11:50:39 -0400 (EDT) > > Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > > > >> ----- On Apr 10, 2019, at 6:32 AM, schwidefsky schwidefsky@de.ibm.com wrote: > >> > >> > On Tue, 9 Apr 2019 15:32:22 -0400 (EDT) > >> > Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote: > >> > > >> >> Hi, > >> >> > >> >> We are about to include the code signature required prior to restartable > >> >> sequences abort handlers into glibc, which will make this ABI choice final. > >> >> We need architecture maintainer input on that signature value. > >> >> > >> >> That code signature is placed before each abort handler, so the kernel can > >> >> validate that it is indeed jumping to an abort handler (and not some > >> >> arbitrary attacker-chosen code). The signature is never executed. > >> >> > >> >> The current discussion thread on the glibc mailing list leads us towards > >> >> using a trap with uncommon immediate operand, which simplifies integration > >> >> with disassemblers, emulators, makes it easier to debug if the control > >> >> flow gets redirected there by mistake, and is nicer for some architecture's > >> >> speculative execution. > >> >> > >> >> We can have different signatures for each sub-architecture, as long as they > >> >> don't have to co-exist within the same process. We can special-case with > >> >> #ifdef for each sub-architecture and endianness if need be. If the architecture > >> >> has instruction set extensions that can co-exist with the architecture > >> >> instruction set within the same process, we need to take into account to which > >> >> instruction the chosen signature value would map (and possibly decide if we > >> >> need to extend rseq to support many signatures). > >> >> > >> >> Here is an example of rseq signature definition template: > >> >> > >> >> /* > >> >> * TODO: document trap instruction objdump output on each sub-architecture > >> >> * instruction sets, as well as instruction set extensions. > >> >> */ > >> >> #define RSEQ_SIG 0x######## > >> >> > >> >> Ideally we'd need a patch on top of the Linux kernel > >> >> tools/testing/selftests/rseq/rseq-s390.h file that updates > >> >> the signature value, so I can then pick it up for the glibc > >> >> patchset. > >> > > >> > The trap4 instruction is a suitable one. The patch would look like this > >> > >> Great! I'm picking it up into my rseq tree if that's OK with you. > > > > Just added the patch to s390/linux:features for the next merge window as well. > > Sounds good! I'll carry it in my tree to have a comprehensive up-to-date list of > rseq signatures for all architectures in a single tree. Worse-case the exact same > change will be pulled from both architecture and rseq trees, which I don't think > should be an issue, right ? Should be fine, the worst that can happen is a minor merge conflict.
diff --git a/tools/testing/selftests/rseq/rseq-s390.h b/tools/testing/selftests/rseq/rseq-s390.h index 1069e85258ce..d4c8e1147d86 100644 --- a/tools/testing/selftests/rseq/rseq-s390.h +++ b/tools/testing/selftests/rseq/rseq-s390.h @@ -1,6 +1,13 @@ /* SPDX-License-Identifier: LGPL-2.1 OR MIT */ -#define RSEQ_SIG 0x53053053 +/* + * RSEQ_SIG uses the trap4 instruction. As Linux does not make use of the + * access-register mode nor the linkage stack this instruction will always + * cause a special-operation exception (the trap-enabled bit in the DUCT + * is and will stay 0). The instruction pattern is + * b2 ff 0f ff trap4 4095(%r0) + */ +#define RSEQ_SIG 0xB2FF0FFF #define rseq_smp_mb() __asm__ __volatile__ ("bcr 15,0" ::: "memory") #define rseq_smp_rmb() rseq_smp_mb()