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Wed, 16 Oct 2019 16:10:49 +0000 From: Song Liu To: Oleg Nesterov CC: open list , "linux-mm@kvack.org" , "akpm@linux-foundation.org" , "matthew.wilcox@oracle.com" , Kernel Team , "william.kucharski@oracle.com" , "Kirill A . Shutemov" , Srikar Dronamraju Subject: Re: [PATCH 4/4] uprobe: only do FOLL_SPLIT_PMD for uprobe register Thread-Topic: [PATCH 4/4] uprobe: only do FOLL_SPLIT_PMD for uprobe register Thread-Index: AQHVg/TTl1jUwKEEhEe4JMFjXQBksqddLX+AgABDI4A= Date: Wed, 16 Oct 2019 16:10:49 +0000 Message-ID: References: <20191016073731.4076725-1-songliubraving@fb.com> <20191016073731.4076725-5-songliubraving@fb.com> <20191016121031.GA31585@redhat.com> In-Reply-To: <20191016121031.GA31585@redhat.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3594.4.19) x-originating-ip: [2620:10d:c090:200::1:35f7] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: f833eda3-5037-4061-1739-08d752536944 x-ms-traffictypediagnostic: MWHPR15MB1360: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:6790; x-forefront-prvs: 0192E812EC x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(346002)(39860400002)(396003)(366004)(376002)(136003)(189003)(199004)(6116002)(64756008)(8676002)(6512007)(66556008)(6246003)(6506007)(54906003)(316002)(229853002)(478600001)(81156014)(86362001)(71200400001)(486006)(476003)(71190400001)(33656002)(50226002)(81166006)(6436002)(186003)(102836004)(46003)(66476007)(76116006)(66446008)(6916009)(446003)(305945005)(66946007)(53546011)(11346002)(2616005)(7736002)(76176011)(14444005)(2906002)(14454004)(256004)(99286004)(6486002)(25786009)(4326008)(36756003)(8936002)(5660300002);DIR:OUT;SFP:1102;SCL:1;SRVR:MWHPR15MB1360;H:MWHPR15MB1165.namprd15.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;MX:1;A:1; received-spf: None (protection.outlook.com: fb.com does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: gD7QeNp7jW9EDkRJgYqRFBP3Z2osBfBS4C+DiI5k2mQ3+1rGYlPIWPSrj2sUpLJjKtHjDstYIliFdYbN3DcFdD1gHjw5Vv2o5l05VtgeCNwdOhF7DIUKUfExfQlo1Hp1gI1c7b9iSmQ4phnjk69b3yrt8uz7ReTy8nnA55QVg6lk56CPtnCT1C7f78LF8OKcrPGYpS04SBIqaoTBv7RJ2jR0s9R2sNNxSm0yM/9GiVI/GMHmW/ezK2XraW4s8YHaJ/OGiH1DzzeFUQTSUXhn/pataKhs8PTOn2RqvgbVKGkoVw8GHLLn5Xu6rjEzKWez+lyUh3TUhv09vr7B9sJOxUZj8a8lepPI+wzXYwdyo2u014nZNHOTz+NEsljyFRlL+fididLNVRFmpBV9HB5435qlHQ4qvmrXMxkLwFDAjPo= Content-Type: text/plain; charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: f833eda3-5037-4061-1739-08d752536944 X-MS-Exchange-CrossTenant-originalarrivaltime: 16 Oct 2019 16:10:49.5778 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: n60JP/0m0vc2RSQreU45iujkoUxM7EwykTgNYbS6RqMGzG6c9MLtUKOwp/ROEZrkGlYjAwRDatefkUNv+wIoDQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1360 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,1.0.8 definitions=2019-10-16_07:2019-10-16,2019-10-16 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 adultscore=0 mlxscore=0 mlxlogscore=999 suspectscore=0 bulkscore=0 clxscore=1015 impostorscore=0 malwarescore=0 spamscore=0 lowpriorityscore=0 phishscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1908290000 definitions=main-1910160135 X-FB-Internal: deliver X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > On Oct 16, 2019, at 5:10 AM, Oleg Nesterov wrote: >=20 > On 10/16, Song Liu wrote: >>=20 >> --- a/kernel/events/uprobes.c >> +++ b/kernel/events/uprobes.c >> @@ -474,14 +474,17 @@ int uprobe_write_opcode(struct arch_uprobe *auprob= e, struct mm_struct *mm, >> struct vm_area_struct *vma; >> int ret, is_register, ref_ctr_updated =3D 0; >> bool orig_page_huge =3D false; >> + unsigned int gup_flags =3D FOLL_FORCE; >>=20 >> is_register =3D is_swbp_insn(&opcode); >> uprobe =3D container_of(auprobe, struct uprobe, arch); >>=20 >> retry: >> + if (is_register) >> + gup_flags |=3D FOLL_SPLIT_PMD; >> /* Read the page with vaddr into memory */ >> - ret =3D get_user_pages_remote(NULL, mm, vaddr, 1, >> - FOLL_FORCE | FOLL_SPLIT_PMD, &old_page, &vma, NULL); >> + ret =3D get_user_pages_remote(NULL, mm, vaddr, 1, gup_flags, >> + &old_page, &vma, NULL); >> if (ret <=3D 0) >> return ret; >>=20 >> @@ -489,6 +492,9 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe,= struct mm_struct *mm, >> if (ret <=3D 0) >> goto put_old; >>=20 >> + WARN(!is_register && PageCompound(old_page), >> + "uprobe unregister should never work on compound page\n"); >=20 > But this can happen with the change above. You can't know if *vaddr was > previously changed by install_breakpoint() or not. > If not, verify_opcode() should likely save us, but we can't rely on it. > Say, someone can write "int3" into vm_file at uprobe->offset. I think this won't really happen. With is_register =3D=3D false, we already= =20 know opcode is not "int3", so current call must be from set_orig_insn().=20 Therefore, old_page must be installed by uprobe, and cannot be compound. The other way is not guaranteed. With is_register =3D=3D true, it is still possible current call is from set_orig_insn(). However, we do not rely on this path.=20 Does this make sense? Or did I miss anything? >=20 > And I am not sure it is safe to continue in this case, I'd suggest to > return -EWHATEVER to avoid the possible crash. I think we can return -ESOMETHING here to be safe. However, if the=20 analysis above makes sense, it is not necessary.=20 Thanks, Song