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([2a02:8084:e84:2480:228:f8ff:fe6f:83a8]) by smtp.gmail.com with ESMTPSA id y10sm26483889wru.94.2020.11.03.13.08.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Nov 2020 13:08:46 -0800 (PST) Subject: Re: [PATCH] x86/mpx: fix recursive munmap() corruption To: Laurent Dufour , Christophe Leroy , Michael Ellerman Cc: Dave Hansen , Thomas Gleixner , Dave Hansen , mhocko@suse.com, rguenther@suse.de, x86@kernel.org, LKML , stable@vger.kernel.org, luto@amacapital.net, linux-mm@kvack.org, Andrew Morton , linuxppc-dev@lists.ozlabs.org, vbabka@suse.cz References: <20190401141549.3F4721FE@viggo.jf.intel.com> <87d0lht1c0.fsf@concordia.ellerman.id.au> <6718ede2-1fcb-1a8f-a116-250eef6416c7@linux.vnet.ibm.com> <4f43d4d4-832d-37bc-be7f-da0da735bbec@intel.com> <4e1bbb14-e14f-8643-2072-17b4cdef5326@linux.vnet.ibm.com> <87k1faa2i0.fsf@concordia.ellerman.id.au> <9c2b2826-4083-fc9c-5a4d-c101858dd560@linux.vnet.ibm.com> <12313ba8-75b5-d44d-dbc0-0bf2c87dfb59@csgroup.eu> <452b347c-0a86-c710-16ba-5a98c12a47e3@linux.vnet.ibm.com> From: Dmitry Safonov <0x7f454c46@gmail.com> Message-ID: <02389b9c-141c-f5b7-756a-516599063766@gmail.com> Date: Tue, 3 Nov 2020 21:08:45 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <452b347c-0a86-c710-16ba-5a98c12a47e3@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable 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: Hi Laurent, Christophe, Michael, all, On 11/3/20 5:11 PM, Laurent Dufour wrote: > Le 23/10/2020 =C3=A0 14:28, Christophe Leroy a =C3=A9crit=C2=A0: [..] >>>> That seems like it would work for CRIU and make sense in general? >>> >>> Sorry for the late answer, yes this would make more sense. >>> >>> Here is a patch doing that. >>> >> >> In your patch, the test seems overkill: >> >> +=C2=A0=C2=A0=C2=A0 if ((start <=3D vdso_base && vdso_end <=3D end) ||= =C2=A0 /* 1=C2=A0=C2=A0 */ >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 (vdso_base <=3D start && s= tart < vdso_end) || /* 3,4 */ >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 (vdso_base < end && end <=3D= vdso_end))=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 /* 2,3 */ >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 mm->context.vdso_base =3D = mm->context.vdso_end =3D 0; >> >> What about >> >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0if (start < vdso_end && vdso_start < end= ) >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 mm->context.vdso_base= =3D mm->context.vdso_end =3D 0; >> >> This should cover all cases, or am I missing something ? >> >> >> And do we really need to store vdso_end in the context ? >> I think it should be possible to re-calculate it: the size of the VDSO >> should be (&vdso32_end - &vdso32_start) + PAGE_SIZE for 32 bits VDSO, >> and (&vdso64_end - &vdso64_start) + PAGE_SIZE for the 64 bits VDSO. >=20 > Thanks Christophe for the advise. >=20 > That is covering all the cases, and indeed is similar to the Michael's > proposal I missed last year. >=20 > I'll send a patch fixing this issue following your proposal. It's probably not necessary anymore. I've sent patches [1], currently in akpm, the last one forbids splitting of vm_special_mapping. So, a user is able munmap() or mremap() vdso as a whole, but not partly. [1]: https://lore.kernel.org/linux-mm/20201013013416.390574-1-dima@arista.com/ Thanks, Dmitry