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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 31 Mar 2020 07:44:29 +0100 Received: from b06wcsmtp001.portsmouth.uk.ibm.com (b06wcsmtp001.portsmouth.uk.ibm.com [9.149.105.160]) by b06avi18626390.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 02V6hQID50856256 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 31 Mar 2020 06:43:26 GMT Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0B552A405F; Tue, 31 Mar 2020 06:44:30 +0000 (GMT) Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9E18DA4060; Tue, 31 Mar 2020 06:44:29 +0000 (GMT) Received: from localhost (unknown [9.85.74.140]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 31 Mar 2020 06:44:29 +0000 (GMT) Date: Tue, 31 Mar 2020 12:14:27 +0530 From: "Naveen N. Rao" Subject: Re: [PATCH 10/12] powerpc/entry32: Blacklist exception entry points for kprobe. To: Benjamin Herrenschmidt , Christophe Leroy , Michael Ellerman , Paul Mackerras References: <1585588031.jvow7mwq4x.naveen@linux.ibm.com> <7f367f35-1bb8-bbb6-f399-8e911f76e043@c-s.fr> <83053ddf-9ba6-d551-6711-890c3f3810b5@c-s.fr> <1585635379.0xixuk2jdc.naveen@linux.ibm.com> In-Reply-To: MIME-Version: 1.0 User-Agent: astroid/v0.15-13-gb675b421 (https://github.com/astroidmail/astroid) Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 x-cbid: 20033106-0028-0000-0000-000003EF2CA4 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20033106-0029-0000-0000-000024B4AE22 Message-Id: <1585637023.fay3842pux.naveen@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.676 definitions=2020-03-31_02:2020-03-30, 2020-03-31 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 mlxscore=0 lowpriorityscore=0 mlxlogscore=999 clxscore=1015 bulkscore=0 malwarescore=0 suspectscore=0 phishscore=0 priorityscore=1501 spamscore=0 adultscore=0 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2003310048 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: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Christophe Leroy wrote: >=20 >=20 > Le 31/03/2020 =C3=A0 08:17, Naveen N. Rao a =C3=A9crit=C2=A0: >> Christophe Leroy wrote: >>> >>> >>> Le 30/03/2020 =C3=A0 20:33, Christophe Leroy a =C3=A9crit=C2=A0: >>>> >>>> >>>> Le 30/03/2020 =C3=A0 19:08, Naveen N. Rao a =C3=A9crit=C2=A0: >>>>> Christophe Leroy wrote: >>>>>> kprobe does not handle events happening in real mode. >>>>>> >>>>>> As exception entry points are running with MMU disabled, >>>>>> blacklist them. >>>>>> >>>>>> Signed-off-by: Christophe Leroy >>>>>> --- >>>>>> =C2=A0arch/powerpc/kernel/entry_32.S | 7 +++++++ >>>>>> =C2=A01 file changed, 7 insertions(+) >>>>>> >>>>>> diff --git a/arch/powerpc/kernel/entry_32.S=20 >>>>>> b/arch/powerpc/kernel/entry_32.S >>>>>> index 94f78c03cb79..9a1a45d6038a 100644 >>>>>> --- a/arch/powerpc/kernel/entry_32.S >>>>>> +++ b/arch/powerpc/kernel/entry_32.S >>>>>> @@ -51,6 +51,7 @@ mcheck_transfer_to_handler: >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 mfspr=C2=A0=C2=A0=C2=A0 r0,SPRN_DSRR1 >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 stw=C2=A0=C2=A0=C2=A0 r0,_DSRR1(r11) >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 /* fall through */ >>>>>> +_ASM_NOKPROBE_SYMBOL(mcheck_transfer_to_handler) >>>>>> >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 .globl=C2=A0=C2=A0=C2=A0 debug_transfer_to_= handler >>>>>> =C2=A0debug_transfer_to_handler: >>>>>> @@ -59,6 +60,7 @@ debug_transfer_to_handler: >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 mfspr=C2=A0=C2=A0=C2=A0 r0,SPRN_CSRR1 >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 stw=C2=A0=C2=A0=C2=A0 r0,_CSRR1(r11) >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 /* fall through */ >>>>>> +_ASM_NOKPROBE_SYMBOL(debug_transfer_to_handler) >>>>>> >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 .globl=C2=A0=C2=A0=C2=A0 crit_transfer_to_h= andler >>>>>> =C2=A0crit_transfer_to_handler: >>>>>> @@ -94,6 +96,7 @@ crit_transfer_to_handler: >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 rlwinm=C2=A0=C2=A0=C2=A0 r0,r1,0,0,(31 - TH= READ_SHIFT) >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 stw=C2=A0=C2=A0=C2=A0 r0,KSP_LIMIT(r8) >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 /* fall through */ >>>>>> +_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler) >>>>>> =C2=A0#endif >>>>>> >>>>>> =C2=A0#ifdef CONFIG_40x >>>>>> @@ -115,6 +118,7 @@ crit_transfer_to_handler: >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 rlwinm=C2=A0=C2=A0=C2=A0 r0,r1,0,0,(31 - TH= READ_SHIFT) >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 stw=C2=A0=C2=A0=C2=A0 r0,KSP_LIMIT(r8) >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 /* fall through */ >>>>>> +_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler) >>>>>> =C2=A0#endif >>>>>> >>>>>> =C2=A0/* >>>>>> @@ -127,6 +131,7 @@ crit_transfer_to_handler: >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 .globl=C2=A0=C2=A0=C2=A0 transfer_to_handle= r_full >>>>>> =C2=A0transfer_to_handler_full: >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 SAVE_NVGPRS(r11) >>>>>> +_ASM_NOKPROBE_SYMBOL(transfer_to_handler_full) >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 /* fall through */ >>>>>> >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 .globl=C2=A0=C2=A0=C2=A0 transfer_to_handle= r >>>>>> @@ -286,6 +291,8 @@ reenable_mmu: >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 lwz=C2=A0=C2=A0=C2=A0 r2, GPR2(r11) >>>>>> =C2=A0=C2=A0=C2=A0=C2=A0 b=C2=A0=C2=A0=C2=A0 fast_exception_return >>>>>> =C2=A0#endif >>>>>> +_ASM_NOKPROBE_SYMBOL(transfer_to_handler) >>>>>> +_ASM_NOKPROBE_SYMBOL(transfer_to_handler_cont) >>>>> >>>>> These are added after 'reenable_mmu', which is itself not=20 >>>>> blacklisted. Is that intentional? >>>> >>>> Yes I put it as the complete end of the entry part, ie just before=20 >>>> stack_ovf which is a function by itself. >>>> >>>> Note that reenable_mmu is inside an #ifdef CONFIG_TRACE_IRQFLAGS. >>>> >>>> I'm not completely sure where to put the _ASM_NOKPROBE_SYMBOL()s,=20 >>>> that's the reason why I put it close to the symbol itself in my first=20 >>>> series. >>>> >>>> Could you have a look at the code and tell me what looks the most=20 >>>> appropriate as a location to you ? >>>> >>>> https://elixir.bootlin.com/linux/v5.6/source/arch/powerpc/kernel/entry= _32.S#L230=20 >>> >>> >>> Ok, thinking about it once more, I guess we have a problem as=20 >>> everything after that reenable_mmu will be visible. >>=20 >> I see that we reach reenable_mmu through a 'rfi' with MSR_KERNEL, which=20 >> seems safe to me. So, I figured it can be probed without issues? >=20 > Yes it can. And that's the reason why I didn't blacklist it. However the=20 > 4: and 7: which are after reenable_mmu are called from earlier, at a=20 > time we are still in real mode. So I need to do something about that I=20 > guess. Ah yes, good catch. Makes sense to move 'reenable_mmu' after all. Thanks, Naveen