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Fri, 01 Mar 2024 17:51:09 -0800 (PST) Received: from www.outflux.net ([198.0.35.241]) by smtp.gmail.com with ESMTPSA id rm12-20020a17090b3ecc00b002993f72ed02sm3845854pjb.34.2024.03.01.17.51.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 01 Mar 2024 17:51:08 -0800 (PST) Date: Fri, 1 Mar 2024 17:51:08 -0800 From: Kees Cook To: "Edgecombe, Rick P" Cc: "christophe.leroy@csgroup.eu" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "luto@kernel.org" , "dave.hansen@linux.intel.com" , "debug@rivosinc.com" , "akpm@linux-foundation.org" , "linux-sh@vger.kernel.org" , "linux-csky@vger.kernel.org" , "mingo@redhat.com" , "kirill.shutemov@linux.intel.com" , "tglx@linutronix.de" , "linux-parisc@vger.kernel.org" , "loongarch@lists.linux.dev" , "linux-mm@kvack.org" , "linux-snps-arc@lists.infradead.org" , "Liam.Howlett@oracle.com" , "hpa@zytor.com" , "peterz@infradead.org" , "linuxppc-dev@lists.ozlabs.org" , "bp@alien8.de" , "linux-s390@vger.kernel.org" , "linux-alpha@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-mips@vger.kernel.org" , "sparclinux@vger.kernel.org" , "broonie@kernel.org" Subject: Re: [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info Message-ID: <202403011747.9ECFAD060B@keescook> References: <20240226190951.3240433-1-rick.p.edgecombe@intel.com> <20240226190951.3240433-6-rick.p.edgecombe@intel.com> <94a2b919-e03b-4ade-b13e-7774849dc02b@csgroup.eu> <202402271004.7145FDB53F@keescook> <8265f804-4540-4858-adc3-a09c11a677eb@csgroup.eu> <91384b505cb78b9d9b71ad58e037c1ed8dfb10d1.camel@intel.com> <202402280912.33AEE7A9CF@keescook> 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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Sat, Mar 02, 2024 at 12:47:08AM +0000, Edgecombe, Rick P wrote: > On Wed, 2024-02-28 at 09:21 -0800, Kees Cook wrote: > > I totally understand. If the "uninitialized" warnings were actually > > reliable, I would agree. I look at it this way: > > > > - initializations can be missed either in static initializers or via > >   run time initializers. (So the risk of mistake here is matched -- > >   though I'd argue it's easier to *find* static initializers when > > adding > >   new struct members.) > > - uninitialized warnings are inconsistent (this becomes an unknown > > risk) > > - when a run time initializer is missed, the contents are whatever > > was > >   on the stack (high risk) > > - what a static initializer is missed, the content is 0 (low risk) > > > > I think unambiguous state (always 0) is significantly more important > > for > > the safety of the system as a whole. Yes, individual cases maybe bad > > ("what uid should this be? root?!") but from a general memory safety > > perspective the value doesn't become potentially influenced by order > > of > > operations, leftover stack memory, etc. > > > > I'd agree, lifting everything into a static initializer does seem > > cleanest of all the choices. > > Hi Kees, > > Well, I just gave this a try. It is giving me flashbacks of when I last > had to do a tree wide change that I couldn't fully test and the > breakage was caught by Linus. Yeah, testing isn't fun for these kinds of things. This is traditionally why the "obviously correct" changes tend to have an easier time landing (i.e. adding "= {}" to all of them). > Could you let me know if you think this is additionally worthwhile > cleanup outside of the guard gap improvements of this series? Because I > was thinking a more cowardly approach could be a new vm_unmapped_area() > variant that takes the new start gap member as a separate argument > outside of struct vm_unmapped_area_info. It would be kind of strange to > keep them separate, but it would be less likely to bump something. I think you want a new member -- AIUI, that's what that struct is for. Looking at this resulting set of patches, I do kinda think just adding the "= {}" in a single patch is more sensible. Having to split things that are know at the top of the function from the stuff known at the existing initialization time is rather awkward. Personally, I think a single patch that sets "= {}" for all of them and drop the all the "= 0" or "= NULL" assignments would be the cleanest way to go. -Kees -- Kees Cook