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Rao" Subject: Re: [PATCH 10/12] powerpc/entry32: Blacklist exception entry points for kprobe. To: Benjamin Herrenschmidt , Christophe Leroy , Michael Ellerman , Paul Mackerras Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org 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: 8BIT 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 lowpriorityscore=0 suspectscore=0 impostorscore=0 mlxscore=0 phishscore=0 clxscore=1015 bulkscore=0 malwarescore=0 spamscore=0 mlxlogscore=999 adultscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2003310048 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christophe Leroy wrote: > > > Le 31/03/2020 à 08:17, Naveen N. Rao a écrit : >> Christophe Leroy wrote: >>> >>> >>> Le 30/03/2020 à 20:33, Christophe Leroy a écrit : >>>> >>>> >>>> Le 30/03/2020 à 19:08, Naveen N. Rao a écrit : >>>>> 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 >>>>>> --- >>>>>>  arch/powerpc/kernel/entry_32.S | 7 +++++++ >>>>>>  1 file changed, 7 insertions(+) >>>>>> >>>>>> diff --git a/arch/powerpc/kernel/entry_32.S >>>>>> 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: >>>>>>      mfspr    r0,SPRN_DSRR1 >>>>>>      stw    r0,_DSRR1(r11) >>>>>>      /* fall through */ >>>>>> +_ASM_NOKPROBE_SYMBOL(mcheck_transfer_to_handler) >>>>>> >>>>>>      .globl    debug_transfer_to_handler >>>>>>  debug_transfer_to_handler: >>>>>> @@ -59,6 +60,7 @@ debug_transfer_to_handler: >>>>>>      mfspr    r0,SPRN_CSRR1 >>>>>>      stw    r0,_CSRR1(r11) >>>>>>      /* fall through */ >>>>>> +_ASM_NOKPROBE_SYMBOL(debug_transfer_to_handler) >>>>>> >>>>>>      .globl    crit_transfer_to_handler >>>>>>  crit_transfer_to_handler: >>>>>> @@ -94,6 +96,7 @@ crit_transfer_to_handler: >>>>>>      rlwinm    r0,r1,0,0,(31 - THREAD_SHIFT) >>>>>>      stw    r0,KSP_LIMIT(r8) >>>>>>      /* fall through */ >>>>>> +_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler) >>>>>>  #endif >>>>>> >>>>>>  #ifdef CONFIG_40x >>>>>> @@ -115,6 +118,7 @@ crit_transfer_to_handler: >>>>>>      rlwinm    r0,r1,0,0,(31 - THREAD_SHIFT) >>>>>>      stw    r0,KSP_LIMIT(r8) >>>>>>      /* fall through */ >>>>>> +_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler) >>>>>>  #endif >>>>>> >>>>>>  /* >>>>>> @@ -127,6 +131,7 @@ crit_transfer_to_handler: >>>>>>      .globl    transfer_to_handler_full >>>>>>  transfer_to_handler_full: >>>>>>      SAVE_NVGPRS(r11) >>>>>> +_ASM_NOKPROBE_SYMBOL(transfer_to_handler_full) >>>>>>      /* fall through */ >>>>>> >>>>>>      .globl    transfer_to_handler >>>>>> @@ -286,6 +291,8 @@ reenable_mmu: >>>>>>      lwz    r2, GPR2(r11) >>>>>>      b    fast_exception_return >>>>>>  #endif >>>>>> +_ASM_NOKPROBE_SYMBOL(transfer_to_handler) >>>>>> +_ASM_NOKPROBE_SYMBOL(transfer_to_handler_cont) >>>>> >>>>> These are added after 'reenable_mmu', which is itself not >>>>> blacklisted. Is that intentional? >>>> >>>> Yes I put it as the complete end of the entry part, ie just before >>>> 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, >>>> that's the reason why I put it close to the symbol itself in my first >>>> series. >>>> >>>> Could you have a look at the code and tell me what looks the most >>>> appropriate as a location to you ? >>>> >>>> https://elixir.bootlin.com/linux/v5.6/source/arch/powerpc/kernel/entry_32.S#L230 >>> >>> >>> Ok, thinking about it once more, I guess we have a problem as >>> everything after that reenable_mmu will be visible. >> >> I see that we reach reenable_mmu through a 'rfi' with MSR_KERNEL, which >> seems safe to me. So, I figured it can be probed without issues? > > Yes it can. And that's the reason why I didn't blacklist it. However the > 4: and 7: which are after reenable_mmu are called from earlier, at a > time we are still in real mode. So I need to do something about that I > guess. Ah yes, good catch. Makes sense to move 'reenable_mmu' after all. Thanks, Naveen