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Thu, 25 Jul 2019 18:17:10 +0000 Received: from MWHPR15MB1165.namprd15.prod.outlook.com ([fe80::4066:b41c:4397:27b7]) by MWHPR15MB1165.namprd15.prod.outlook.com ([fe80::4066:b41c:4397:27b7%7]) with mapi id 15.20.2094.013; Thu, 25 Jul 2019 18:17:10 +0000 From: Song Liu To: Oleg Nesterov CC: lkml , Linux-MM , "Andrew Morton" , "matthew.wilcox@oracle.com" , "kirill.shutemov@linux.intel.com" , "peterz@infradead.org" , "rostedt@goodmis.org" , "Kernel Team" , "william.kucharski@oracle.com" Subject: Re: [PATCH v8 2/4] uprobe: use original page when all uprobes are removed Thread-Topic: [PATCH v8 2/4] uprobe: use original page when all uprobes are removed Thread-Index: AQHVQfsnepoAlMhPK0qmuIU0gpphb6bZpE2AgAB5kgCAAOAOAIAAqHSA Date: Thu, 25 Jul 2019 18:17:10 +0000 Message-ID: References: <20190724083600.832091-1-songliubraving@fb.com> <20190724083600.832091-3-songliubraving@fb.com> <20190724113711.GE21599@redhat.com> <20190725081414.GB4707@redhat.com> In-Reply-To: <20190725081414.GB4707@redhat.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: Apple Mail (2.3445.104.11) x-originating-ip: [2620:10d:c090:200::3:63dc] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 06967bf3-325c-4572-da0f-08d7112c4f45 x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600148)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:MWHPR15MB1279; 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charset="us-ascii" Content-ID: <8D5E5C7D092DC2418E8E69FF9C0E6753@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 06967bf3-325c-4572-da0f-08d7112c4f45 X-MS-Exchange-CrossTenant-originalarrivaltime: 25 Jul 2019 18:17:10.0784 (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: songliubraving@fb.com X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR15MB1279 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-07-25_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1907250215 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Jul 25, 2019, at 1:14 AM, Oleg Nesterov wrote: >=20 > On 07/24, Song Liu wrote: >>=20 >>=20 >>> On Jul 24, 2019, at 4:37 AM, Oleg Nesterov wrote: >>>=20 >>> On 07/24, Song Liu wrote: >>>>=20 >>>> lock_page(old_page); >>>> @@ -177,15 +180,24 @@ static int __replace_page(struct vm_area_struct = *vma, unsigned long addr, >>>> mmu_notifier_invalidate_range_start(&range); >>>> err =3D -EAGAIN; >>>> if (!page_vma_mapped_walk(&pvmw)) { >>>> - mem_cgroup_cancel_charge(new_page, memcg, false); >>>> + if (!orig) >>>> + mem_cgroup_cancel_charge(new_page, memcg, false); >>>> goto unlock; >>>> } >>>> VM_BUG_ON_PAGE(addr !=3D pvmw.address, old_page); >>>>=20 >>>> get_page(new_page); >>>> - page_add_new_anon_rmap(new_page, vma, addr, false); >>>> - mem_cgroup_commit_charge(new_page, memcg, false, false); >>>> - lru_cache_add_active_or_unevictable(new_page, vma); >>>> + if (orig) { >>>> + lock_page(new_page); /* for page_add_file_rmap() */ >>>> + page_add_file_rmap(new_page, false); >>>=20 >>>=20 >>> Shouldn't we re-check new_page->mapping after lock_page() ? Or we can't >>> race with truncate? >>=20 >> We can't race with truncate, because the file is open as binary and >> protected with DENYWRITE (ETXTBSY). >=20 > No. Yes, deny_write_access() protects mm->exe_file, but not the dynamic > libraries or other files which can be mmaped. I see. Let me see how we can cover this.=20 >=20 >>> and I am worried this code can try to lock the same page twice... >>> Say, the probed application does MADV_DONTNEED and then writes "int3" >>> into vma->vm_file at the same address to fool verify_opcode(). >>>=20 >>=20 >> Do you mean the case where old_page =3D=3D new_page? >=20 > Yes, >=20 >> I think this won't >> happen, because in uprobe_write_opcode() we only do orig_page for >> !is_register case. >=20 > See above. >=20 > !is_register doesn't necessarily mean the original page was previously co= w'ed. > And even if it was cow'ed, MADV_DONTNEED can restore the original mapping= . I guess I know the case now. We can probably avoid this with an simp=10le=20 check for old_page =3D=3D new_page? Thanks, Song