Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   "Jose E. Marchesi" <jose.marchesi@oracle.com>
To:     Yonghong Song <yhs@meta.com>
Cc:     Peter Foley <pefoley2@pefoley.com>,
        Eduard Zingerman <eddyz87@gmail.com>,
        Quentin Monnet <quentin@isovalent.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, bpf@vger.kernel.org,
        linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
        david.faust@oracle.com, elena.zannoni@oracle.com
Subject: Re: [PATCH] tools: bpf: Disable stack protector
References: <20230114-bpf-v1-1-f836695a8b62@pefoley.com>
        <cb03b745-26b8-706c-de40-80ae991e29fd@isovalent.com>
        <194f38f2dc7d521375e5a660baaf1be31536be9a.camel@gmail.com>
        <CAOFdcFOgAH1z7EKyM=Q4EvzLuKETOWWDMwuqp36SxV-X6PGP5Q@mail.gmail.com>
        <1135125e-6b8a-7b75-5f0b-3208f6b6e8ae@meta.com>
Date:   Tue, 17 Jan 2023 14:23:51 +0100
In-Reply-To: <1135125e-6b8a-7b75-5f0b-3208f6b6e8ae@meta.com> (Yonghong Song's
        message of "Mon, 16 Jan 2023 23:05:15 -0800")
Message-ID: <87bkmx9tw8.fsf@oracle.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux)
Content-Type: text/plain
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?BZ6ygcgLg9TpksJb9S/2AXWRlQMm94vntEiANtsBPQJ98tuVpaWtXmjxCZPb?=
 =?us-ascii?Q?sMII49Giol1zjD1c9e5CLFQLRyb80zXAlBwFVTqVbUkpVlroRc5uFzfOtOLH?=
 =?us-ascii?Q?FFkYaXzr4ZsB878MRP4CBqfFlILx0ShJbGyhEp5DNj94DlBlVQDaKUiBwpdz?=
 =?us-ascii?Q?APn1PL3jU5C1bCjMEbUtgx56nanMcTwWgqiyyqFBMKG+U5Fr3nQ3CN4EEZ7i?=
 =?us-ascii?Q?SNsizOgYAcNz1UDnXA6JEXSLDi/UqhEBjej6yXbTnvdH/Ga4Y72CIapqdLEK?=
 =?us-ascii?Q?kMWZ7sPnwuVQAwU/E1SuJ9IrNr4iSnPFZTFAP0ztTZtdt4McZQac0ZL7l/Qv?=
 =?us-ascii?Q?FhDO9twvA5K9QFxfeqJGB/NS3ZJgOESZRwPrSfjxNqHo4hmrzqdQDt20kaM9?=
 =?us-ascii?Q?ZKNF/7LNPeikC5clRxzT/7jyZraTqHdCSE7pKnqoFc58QHuG61olkFPTAyif?=
 =?us-ascii?Q?sSHvPBisCyzwOGJVHjYbLCskejvxa8iXafdQTKoT+YKbHWW4OGLc07LbRS7J?=
 =?us-ascii?Q?8RdQnz+Nex1XOtyO2Mfp/aq2JLwLxOLjrY6mFO+3p9eORbatrW0LCIyT4jJb?=
 =?us-ascii?Q?L7VpZ6B42JUV/cxWL4eBNXlajq7wZdcyo23kuOAQHN2kp2luzACrOWdX0YrQ?=
 =?us-ascii?Q?omDbmc4wpbCAXBRRSNcNiJ7SDy3uvsDLcc00STFwzWkaIDPT7GNnkalgnTlA?=
 =?us-ascii?Q?W8GEPv+eAS8Ri/kktpNZ3mUYwiUEmBfQYxgqbCppCd2H8Ajn4p8ii5XaD1bk?=
 =?us-ascii?Q?cf0PJDkUs3bkFaiGhGiUTI7CrMeUG7mjrSAGBaNlDrbyARpT1KOhS1/A8uoD?=
 =?us-ascii?Q?KWkafpym0cdSW7PV2ZEDgcIVTQf2khIg4w8Wt5Npi5n5a8rQmCtzegs1QV1x?=
 =?us-ascii?Q?sbh2TGd2s6SGSQe1cJmp0Yu4Dt0G+HR54D5XVSBOjzJKPs88X2Idp9MCiNuu?=
 =?us-ascii?Q?+8KldMyVaNlqwPPBxvcnulcFWttIugd6y0ki3piKXXywOD/DpVQTE5rsiPT0?=
 =?us-ascii?Q?H7EmI5yjV9BKG0HK3Xma0NiKBZqdia0Es+HMGxjsNhrr0aKjEJ37ijvGlMx8?=
 =?us-ascii?Q?8He0lJsyLJsOtQqt67Xk3Uj9OBp9P5ViNb5jDxJ5fgsUs80aVOui5ZanMQba?=
 =?us-ascii?Q?fM/YqmMhV9sRWRCccu6m5FT53w2bgO0SBksUToK1/tc7gGCcVtP0Z+8U1QY6?=
 =?us-ascii?Q?NfKyfZ9UkxM94Mrb/N4/cBvJcrtaz5hzqDdz3i8hSt1p+wvrEeWLeF7rbCBk?=
 =?us-ascii?Q?QUavB5MVOoktYH328rFwVvxZYKm4ZOuOkpiyxyLVkPVXIlsPs+P80FgXJ0k8?=
 =?us-ascii?Q?7o2ab4n/FoTKgHfxS8VjjkcdCuNg4fjWeGIHx7sU2upg+2w7szaSHrTAesr7?=
 =?us-ascii?Q?rEIxryLjamBop/cWwGy7h5WJ08whhY2Ki8A3SD6h6c+ZgnVaxWUIfB1LtxXx?=
 =?us-ascii?Q?y51bVLzd+mcMURC6ExV9ksKPlHHaCmuO/auSe1rJWr4BemDPMamI2Vr18wBk?=
 =?us-ascii?Q?4W7KNgzPSGb1mZ0GHZJ3rf69rMBJ5zUiNjxnLixPHhe/jmDRmqQYpcEV2AOJ?=
 =?us-ascii?Q?F01U7kR+TFfQEAL0x78msWfvhPWN9cWvQDO2g29hIWqF/8u9g+7xZbkENVHY?=
 =?us-ascii?Q?Mw=3D=3D?=
X-MS-Exchange-AntiSpam-ExternalHop-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-ExternalHop-MessageData-0: =?us-ascii?Q?Q/N5ThNYa/07mhj/x3IhQKeH9DOd+ZjMRu1UBVzKOZwu2kZbATlTU4JynwR6?=
 =?us-ascii?Q?i6ACbgUG0v6XQ0h5qMcBC+xa7FLfwuE3zUMyzhQQGeuyBFnSeOV4eCJxOOI8?=
 =?us-ascii?Q?lUvspWHoiPu0ErNilgTqSIq1LTCg/JMK8gjlIJp3JwR5kHuiFTJOo3shjpTk?=
 =?us-ascii?Q?kcqv1fzSt9xoDr9/hF+AZRGwyr66TJMkJkXKqm1+C84i4NdqkB650czUO5me?=
 =?us-ascii?Q?ghpMGcnSXXn79RfQH2GTixTBRIJOd1Sr8akf2+sEGU727J86gxlsPYymzoF0?=
 =?us-ascii?Q?swWARaruOMP3vcpHlwesHEgGCc58if4d265hlcPZuyBdKdtyeKCG5/mBlgBR?=
 =?us-ascii?Q?Q73tGN+8I5+WeCobvatOS7zF3ZOSSYUv6EIwwRQIKqrxGC+W6H/ajdGWw6rt?=
 =?us-ascii?Q?nMO8sVTDjbQ9M2/bDu/gT0iHpeTo/522j8KLzsBaM6J7saYJFRpPxIbm6w86?=
 =?us-ascii?Q?eJJeBKWYw9J/SrCmW+5CCFssbPl1VAbT6g+aFxMXtYDnNEOCy9F0XjfFBrNU?=
 =?us-ascii?Q?/AyE0gBuzAdyxw5zOT3CBA2GHMfrj4u8CPHJx8In1AkPIicPkZXGjZEM7Z0A?=
 =?us-ascii?Q?qm4tMi2Z4oyJ0G3ydDThzWn7lw06y82Fh6O6XAYeg1TCCUmxBjKwNI574oQl?=
 =?us-ascii?Q?nKny8FcT4nTNr7pcvDXi1RJRLOjklA9xf1OgzxrfN6G1VFYBoZICrzwmDC7Z?=
 =?us-ascii?Q?7bx7hLvbnvBucs2l7edG++IQl/5SBCjYdcDHCiN39MWn+x6PC5LZ1YAqLRR9?=
 =?us-ascii?Q?MqFWXJwlUr9WgqsJgMxtNOPdA2ZlmlZuBLiC9/DARJnyv9au+goR8RxxEPIM?=
 =?us-ascii?Q?UXHDxKsBoWTM0QnL1cFUUxcQ/b4Qj+htUxXTlCCJkl/xMuwuHbaDGf0DmrUF?=
 =?us-ascii?Q?QQ0mFoalV0lJbYyfmzNmIkPRu6FvhjyLags3lCP8XIYWfUo8bLUbzDoZVJVi?=
 =?us-ascii?Q?SkTBrgMMbcX2xZCelg/o7FsTsz/fImKkDW2EdKfk2X/pX0FAqabqEq1uPsab?=
 =?us-ascii?Q?TICMati75YNDIjnwRMm63TbxrdOHc5VEPt8UlIAQT5chPgK5HWldON1rY61S?=
 =?us-ascii?Q?vfBxxkl7YMYj/NnqVeJPlQ+NdDt8mA=3D=3D?=
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: a1c49f29-bc73-457c-3b7e-08daf88d7a2b
X-MS-Exchange-CrossTenant-AuthSource: BYAPR10MB2888.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Jan 2023 13:19:35.2733
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: wcvgoWCSTcJ7pvtEGGYleFWaCGh1USpk0pqOhOwYPDUFubm16qMDyUA6zn8Lr7CBxhShH7DZkSuILlTlDGOVbNQ1lDY2N/rkcZpdELfV41Y=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR10MB7116
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.219,Aquarius:18.0.923,Hydra:6.0.562,FMLib:17.11.122.1
 definitions=2023-01-17_06,2023-01-17_01,2022-06-22_01
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 phishscore=0
 mlxlogscore=596 adultscore=0 malwarescore=0 suspectscore=0 mlxscore=0
 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1
 engine=8.12.0-2212070000 definitions=main-2301170110
X-Proofpoint-GUID: JiXFHAWt8_Kytj_Qqk5Pmkmnp7iUdIvl
X-Proofpoint-ORIG-GUID: JiXFHAWt8_Kytj_Qqk5Pmkmnp7iUdIvl
X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_LOW,
        RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=ham
        autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


> On 1/16/23 2:49 PM, Peter Foley wrote:
>> On Mon, Jan 16, 2023 at 4:59 AM Eduard Zingerman <eddyz87@gmail.com> wrote:
>>>
>>> A bit tangential, but since BPF LLVM backend does not support the
>>> stack protector (should it?) there is also an option to adjust LLVM
>>> to avoid this instrumentation, WDYT?
>>>
>> That would probably be worth doing, yes.
>> But given that won't help already released versions of clang, it
>> should probably happen in addition to this patch.
>
> Peter,
>
> If I understand correctly (by inspecting clang code), the stack
> protector is off by default. Do you have link to Gentoo build
> page to show how they enable stack protector? cmake config or
> a private patch?
>
> Jose,
>
> How gcc-bpf handle stack protector? The compiler just disables
> stack protector for bpf target?

It doesn't.  -fstack-protector is disabled by default in GCC.  When you
use it you get something like:

  $ echo 'int foo() { char s[256]; return s[3]; }' | bpf-unknown-none-gcc \
    -fstack-protector -S -o foo.s -O2 -xc -
  $ cat foo.s
  	.file	"<stdin>"
  	.text
  	.align	3
  	.global	foo
  	.type	foo, @function
  foo:
  	lddw	%r1,__stack_chk_guard
  	ldxdw	%r0,[%r1+0]
  	stxdw	[%fp+-8],%r0
  	ldxb	%r0,[%fp+-261]
  	lsh	%r0,56
  	arsh	%r0,56
  	ldxdw	%r2,[%fp+-8]
  	ldxdw	%r3,[%r1+0]
 	jne	%r2,%r3,.L4
  	exit
  .L4:
  	call	__stack_chk_fail
  	.size	foo, .-foo
  	.ident	"GCC: (GNU) 12.0.0 20211206 (experimental)"

i.e. it pushes a stack canary and checks it upon function exit, calling
__stack_chk_fail.

If clang has -fstack-protector ON by default and you change the BPF
backend in order to ignore the flag, I think we should do the same in
GCC.