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Thu, 5 Jun 2025 10:21:53 +0000 (GMT) Message-ID: <2dfdc293-beef-4a67-8173-00697d1fcc8c@linux.ibm.com> Date: Thu, 5 Jun 2025 12:21:53 +0200 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] s390/mm: Fix in_atomic() handling in do_secure_storage_access() To: Heiko Carstens Cc: Alexander Gordeev , Claudio Imbrenda , Janosch Frank , David Hildenbrand , Sven Schnelle , Vasily Gorbik , kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org References: <20250603134936.1314139-1-hca@linux.ibm.com> <20250604184855.44793208@p-imbrenda> <20250604194043.0ab9535e@p-imbrenda> <408922a2-ec1a-4e60-841a-90714a3310de@linux.ibm.com> <20250605100743.7808A03-hca@linux.ibm.com> Content-Language: en-US From: Christian Borntraeger In-Reply-To: <20250605100743.7808A03-hca@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=Pq2TbxM3 c=1 sm=1 tr=0 ts=68416fc7 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=6IFa9wvqVegA:10 a=VnNF1IyMAAAA:8 a=EelIrjACvyVQsPZcEQcA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNjA1MDA4OCBTYWx0ZWRfX271KAbKZwllO N5Sbm5P3FGIqcnRhBJMdG69KMqOsG8XvA+DBldvCusvy7AdjumNIN1tG8Oe2m1qln1KdmoyErzp wljFy5RxnicyGHRpfuLimBPOoZrq24Ub+gOwSqrzQps0ubzDvIlQ3Vav0zXTT5hvPbU2Z40QI0f LtKOjdQCx4X53JqRRLvE0x6bJjkK403oBKp2vuXAK1MTEUn85+MFi7FLaYAinwL0bsiuHq0BhmI 9LUu/zmbyVozJP/1S7zMlfGjy1sUneV+9Mh1dOaVhO6M5yEcMfdXeWxQ9Wh4ShRV5+yujCCnW/n ULDYjt7Y30H3Y/Nf0oJkbbQMyJWu2rCIjwDQEAz5PGlIMStD3FG5H9h41wVuEWWzWz8NpAC4yE7 xjvH1HKNy13YP4qTtk3SoduxPg763cXmSrwUQTkZ8MQtitqXkvMY4r8MCUT/lfs94gMdU469 X-Proofpoint-GUID: QBZUv65jLo5T9ek5Hw6khQFVufRkancR X-Proofpoint-ORIG-GUID: QBZUv65jLo5T9ek5Hw6khQFVufRkancR X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.0.736,FMLib:17.12.80.40 definitions=2025-06-05_02,2025-06-03_02,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 lowpriorityscore=0 clxscore=1015 malwarescore=0 mlxlogscore=675 phishscore=0 bulkscore=0 spamscore=0 suspectscore=0 priorityscore=1501 mlxscore=0 adultscore=0 classifier=spam authscore=0 authtc=n/a authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2505280000 definitions=main-2506050088 Am 05.06.25 um 12:07 schrieb Heiko Carstens: > On Thu, Jun 05, 2025 at 11:06:29AM +0200, Christian Borntraeger wrote: >> Am 05.06.25 um 11:04 schrieb Alexander Gordeev: >>> On Wed, Jun 04, 2025 at 07:40:43PM +0200, Claudio Imbrenda wrote: >>>>>>> This could trigger WARN_ON_ONCE() in handle_fault_error_nolock(): >>>>>>> >>>>>>> if (WARN_ON_ONCE(!si_code)) >>>>>>> si_code = SEGV_MAPERR; >>>>>>> >>>>>>> Would this warning be justified in this case (aka user_mode(regs) == >>>>>>> true)? >>>>>> >>>>>> I think so, because if we are in usermode, we should never trigger >>>>>> faulthandler_disabled() >>>>> >>>>> I think I do not get you. We are in a system call and also in_atomic(), >>>>> so faulthandler_disabled() is true and handle_fault_error_nolock(regs, 0) >>>>> is called (above). >>>> >>>> what is the psw in regs? >>>> is it not the one that was being used when the exception was triggered? >>> >>> Hmm, right. I assume is_kernel_fault() returns false not because >>> user_mode(regs) is true, but because we access the secondary AS. >>> >>> Still, to me it feels wrong to trigger that warning due to a user >>> process activity. But anyway: >>> >>> Acked-by: Alexander Gordeev >> >> Can we trigger a WARN from userspace? > > No. If the warning triggers, then this indicates a bug in the kernel (exit to > user with faulthandler_disabled() == true). I managed to screw up the kernel > exactly with such a bug. See commit 588a9836a4ef ("s390/stacktrace: Use break > instead of return statement"), which lead to random unexplainable user space > crashes. Ok, then this makes a lot of sense to WARN. Acked-by: Christian Borntraeger