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Howlett" , Kees Cook , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Alexander Gordeev , Sven Schnelle , Vasily Gorbik , Christian Borntraeger , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH mm-unstable 0/2] mseal system mappings fix + s390 enablement Message-ID: <20250311140630.12846Eef-hca@linux.ibm.com> References: <20250311123326.2686682-1-hca@linux.ibm.com> <20250311133736.12846D42-hca@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 4S0zIuxNoDUzIcyMCnnFiJt06R98PYVr X-Proofpoint-ORIG-GUID: 4S0zIuxNoDUzIcyMCnnFiJt06R98PYVr X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1093,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2025-03-11_03,2025-03-11_02,2024-11-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 bulkscore=0 spamscore=0 mlxlogscore=950 suspectscore=0 phishscore=0 priorityscore=1501 adultscore=0 clxscore=1015 malwarescore=0 impostorscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2502100000 definitions=main-2503110089 On Tue, Mar 11, 2025 at 01:42:01PM +0000, Lorenzo Stoakes wrote: > > Just like for arm64, and x86_64 the s390 part is just adding the new > > vm flag to the _install_mappings() call in vdso code. Otherwise there > > is nothing to be considered. > > No, they are not just adding a flag, they are enabling the sealing of > system mappings, if a user chooses to make use of it, which already breaks > a number of useland applications that rely on remapping these. > > if the architecture code ever needs to unmap/remap these, then this breaks > your architecture. > > I think it would be sensible to clearly indicate that enabling this feature > does not break the s390 architecture and you've confirmed that by checking > the code and ensuring that nowhere does it rely upon doing this. > > Likely that's the case, but I'd suggest you ought to make sure... > > x86-64 and arm64 were checked for this and confirmed to not ever need this. > > This is why we're restricting by architecture. Ok, I was assuming more that whoever enables that config option knows what he or she is doing. However as far as I know there is no s390 user space which relies on remapping vdso mappings. When it comes to unmapping vdso: this would break user space since commit df29a7440c4b ("s390/signal: switch to using vdso for sigreturn and syscall restart") - there haven't been any reports.