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Tue, 2 Feb 2021 05:55:22 +0000 (GMT) Received: from skywalker.linux.ibm.com (unknown [9.199.35.92]) by b03ledav004.gho.boulder.ibm.com (Postfix) with ESMTP; Tue, 2 Feb 2021 05:55:22 +0000 (GMT) X-Mailer: emacs 27.1 (via feedmail 11-beta-1 I) From: "Aneesh Kumar K.V" To: Nicholas Piggin , Christophe Leroy , Michael Ellerman , Zorro Lang Subject: Re: [PATCH] powerpc/fault: fix wrong KUAP fault for IO_URING In-Reply-To: <877dnrrsbu.fsf@linux.ibm.com> References: <20210127145648.348135-1-zlang@redhat.com> <1611792928.nw4g8h8kj4.astroid@bobo.none> <20210128031355.GP14354@localhost.localdomain> <66061f75-c8de-c1eb-aaaf-9594a31be790@kernel.dk> <20210128135220.GQ14354@localhost.localdomain> <17ae2706-fe95-a5de-b9da-e3480800daf7@csgroup.eu> <20210129065220.GS14354@localhost.localdomain> <18dd441b-440a-fe95-0907-d8cec5b49410@csgroup.eu> <87r1m2d5z4.fsf@mpe.ellerman.id.au> <1612014260.b4fac0liie.astroid@bobo.none> <877dnrrsbu.fsf@linux.ibm.com> Date: Tue, 02 Feb 2021 11:25:20 +0530 Message-ID: <874kivrp2v.fsf@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.369, 18.0.737 definitions=2021-02-02_03:2021-01-29, 2021-02-02 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 mlxlogscore=999 priorityscore=1501 suspectscore=0 bulkscore=0 lowpriorityscore=0 phishscore=0 adultscore=0 mlxscore=0 clxscore=1015 spamscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2009150000 definitions=main-2102020035 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jens Axboe , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Aneesh Kumar K.V writes: > Nicholas Piggin writes: > >> Excerpts from Michael Ellerman's message of January 30, 2021 9:22 pm: >>> Christophe Leroy writes: >>>> +Aneesh >>>> >>>> Le 29/01/2021 =C3=A0 07:52, Zorro Lang a =C3=A9crit=C2=A0: >>> .. >>>>> [ 96.200296] ------------[ cut here ]------------ >>>>> [ 96.200304] Bug: Read fault blocked by KUAP! >>>>> [ 96.200309] WARNING: CPU: 3 PID: 1876 at arch/powerpc/mm/fault.c:2= 29 bad_kernel_fault+0x180/0x310 >>>> >>>>> [ 96.200734] NIP [c000000000849424] fault_in_pages_readable+0x104/0= x350 >>>>> [ 96.200741] LR [c00000000084952c] fault_in_pages_readable+0x20c/0x= 350 >>>>> [ 96.200747] --- interrupt: 300 >>>> >>>> >>>> Problem happens in a section where userspace access is supposed to be = granted, so the patch you=20 >>>> proposed is definitely not the right fix. >>>> >>>> c000000000849408: 2c 01 00 4c isync >>>> c00000000084940c: a6 03 3d 7d mtspr 29,r9 <=3D=3D granting userspa= ce access permission >>>> c000000000849410: 2c 01 00 4c isync >>>> c000000000849414: 00 00 36 e9 ld r9,0(r22) >>>> c000000000849418: 20 00 29 81 lwz r9,32(r9) >>>> c00000000084941c: 00 02 29 71 andi. r9,r9,512 >>>> c000000000849420: 78 d3 5e 7f mr r30,r26 >>>> =3D=3D> c000000000849424: 00 00 bf 8b lbz r29,0(r31) <=3D=3D acc= essing userspace >>>> c000000000849428: 10 00 82 41 beq c000000000849438 >>>> c00000000084942c: 2c 01 00 4c isync >>>> c000000000849430: a6 03 bd 7e mtspr 29,r21 <=3D=3D clearing usersp= ace access permission >>>> c000000000849434: 2c 01 00 4c isync >>>> >>>> My first guess is that the problem is linked to the following function= , see the comment >>>> >>>> /* >>>> * For kernel thread that doesn't have thread.regs return >>>> * default AMR/IAMR values. >>>> */ >>>> static inline u64 current_thread_amr(void) >>>> { >>>> if (current->thread.regs) >>>> return current->thread.regs->amr; >>>> return AMR_KUAP_BLOCKED; >>>> } >>>> >>>> Above function was introduced by commit 48a8ab4eeb82 ("powerpc/book3s6= 4/pkeys: Don't update SPRN_AMR=20 >>>> when in kernel mode") >>>=20 >>> Yeah that's a bit of a curly one. >>>=20 >>> At some point io_uring did kthread_use_mm(), which is supposed to mean >>> the kthread can operate on behalf of the original process that submitted >>> the IO. >>>=20 >>> But because KUAP is implemented using memory protection keys, it depends >>> on the value of the AMR register, which is not part of the mm, it's in >>> thread.regs->amr. >>>=20 >>> And what's worse by the time we're in kthread_use_mm() we no longer have >>> access to the thread.regs->amr of the original process that submitted >>> the IO. >>>=20 >>> We also can't simply move the AMR into the mm, precisely because it's >>> per thread, not per mm. >>>=20 >>> So TBH I don't know how we're going to fix this. >>>=20 >>> I guess we could return AMR=3Dunblocked for kernel threads, but that's >>> arguably a bug because it allows a process to circumvent memory keys by >>> asking the kernel to do the access. >> >> We shouldn't need to inherit AMR should we? We only need it to be locked= =20 >> for kernel threads until it's explicitly unlocked -- nothing mm specific= =20 >> there. I think current_thread_amr could return 0 for kernel threads? Or >> I would even avoid using that function for allow_user_access and open >> code the kthread case and remove it from current_thread_amr(). >> >> Thanks, >> Nick > updated one >From 8fdb0680f983940d61f91da8252b13c8d3e8ebee Mon Sep 17 00:00:00 2001 From: "Aneesh Kumar K.V" Date: Tue, 2 Feb 2021 09:23:38 +0530 Subject: [PATCH v2] powerpc/kuap: Allow kernel thread to access userspace after kthread_use_mm This fix the bad fault reported by KUAP when io_wqe_worker access userspace. Bug: Read fault blocked by KUAP! WARNING: CPU: 1 PID: 101841 at arch/powerpc/mm/fault.c:229 __do_page_fault= +0x6b4/0xcd0 NIP [c00000000009e7e4] __do_page_fault+0x6b4/0xcd0 LR [c00000000009e7e0] __do_page_fault+0x6b0/0xcd0 .......... Call Trace: [c000000016367330] [c00000000009e7e0] __do_page_fault+0x6b0/0xcd0 (unrelia= ble) [c0000000163673e0] [c00000000009ee3c] do_page_fault+0x3c/0x120 [c000000016367430] [c00000000000c848] handle_page_fault+0x10/0x2c --- interrupt: 300 at iov_iter_fault_in_readable+0x148/0x6f0 .......... NIP [c0000000008e8228] iov_iter_fault_in_readable+0x148/0x6f0 LR [c0000000008e834c] iov_iter_fault_in_readable+0x26c/0x6f0 interrupt: 300 [c0000000163677e0] [c0000000007154a0] iomap_write_actor+0xc0/0x280 [c000000016367880] [c00000000070fc94] iomap_apply+0x1c4/0x780 [c000000016367990] [c000000000710330] iomap_file_buffered_write+0xa0/0x120 [c0000000163679e0] [c00800000040791c] xfs_file_buffered_aio_write+0x314/0x= 5e0 [xfs] [c000000016367a90] [c0000000006d74bc] io_write+0x10c/0x460 [c000000016367bb0] [c0000000006d80e4] io_issue_sqe+0x8d4/0x1200 [c000000016367c70] [c0000000006d8ad0] io_wq_submit_work+0xc0/0x250 [c000000016367cb0] [c0000000006e2578] io_worker_handle_work+0x498/0x800 [c000000016367d40] [c0000000006e2cdc] io_wqe_worker+0x3fc/0x4f0 [c000000016367da0] [c0000000001cb0a4] kthread+0x1c4/0x1d0 [c000000016367e10] [c00000000000dbf0] ret_from_kernel_thread+0x5c/0x6c The kernel consider thread AMR value for kernel thread to be AMR_KUAP_BLOCKED. Hence access to userspace is denied. This of course not correct and we should allow userspace access after kthread_use_mm(). To be precise, kthread_use_mm() should inherit the AMR value of the operating address space. But, the AMR value is thread-specific and we inherit the address space and not thread access restrictions. Because of this ignore AMR value when accessing userspace via kernel thread. Signed-off-by: Aneesh Kumar K.V --- Changes from v1: * Address review feedback from Nick=20 arch/powerpc/include/asm/book3s/64/kup.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/include/asm/book3s/64/kup.h b/arch/powerpc/includ= e/asm/book3s/64/kup.h index f50f72e535aa..95f4df99249e 100644 --- a/arch/powerpc/include/asm/book3s/64/kup.h +++ b/arch/powerpc/include/asm/book3s/64/kup.h @@ -384,7 +384,13 @@ static __always_inline void allow_user_access(void __u= ser *to, const void __user // This is written so we can resolve to a single case at build time BUILD_BUG_ON(!__builtin_constant_p(dir)); =20 - if (mmu_has_feature(MMU_FTR_PKEY)) + /* + * if it is a kthread that did kthread_use_mm() don't + * use current_thread_amr(). + */ + if (current->flags & PF_KTHREAD) + thread_amr =3D 0; + else if (mmu_has_feature(MMU_FTR_PKEY)) thread_amr =3D current_thread_amr(); =20 if (dir =3D=3D KUAP_READ) --=20 2.29.2