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[86.9.19.6]) by smtp.gmail.com with ESMTPSA id a4sm28930843wrg.80.2020.06.26.04.29.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 26 Jun 2020 04:29:28 -0700 (PDT) Date: Fri, 26 Jun 2020 12:29:27 +0100 From: Daniel Thompson To: Sumit Garg Cc: James Bottomley , Jerome Forissier , Maxim Uvarov , Greg Kroah-Hartman , Linux Kernel Mailing List , Jarkko Sakkinen , Arnd Bergmann , "tee-dev @ lists . linaro . org" , Jason Gunthorpe , linux-integrity@vger.kernel.org, peterhuewe@gmx.de Subject: Re: [Tee-dev] [PATCHv8 1/3] optee: use uuid for sysfs driver entry Message-ID: <20200626112927.vfffwdhzdjf6ndmb@holly.lan> References: <1592507935.15159.5.camel@HansenPartnership.com> <1592578844.4369.5.camel@HansenPartnership.com> <1593012069.28403.11.camel@HansenPartnership.com> <1593127902.13253.11.camel@HansenPartnership.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Fri, Jun 26, 2020 at 10:40:41AM +0530, Sumit Garg wrote: > On Fri, 26 Jun 2020 at 05:01, James Bottomley > wrote: > > > > On Thu, 2020-06-25 at 19:54 +0530, Sumit Garg wrote: > > > On Wed, 24 Jun 2020 at 20:51, James Bottomley > > > wrote: > > > > > > > > On Wed, 2020-06-24 at 16:17 +0530, Sumit Garg wrote: > > > > > Apologies for delay in my reply as I was busy with some other > > > > > stuff. > > > > > > > > > > On Fri, 19 Jun 2020 at 20:30, James Bottomley > > > > > wrote: > > > > > > > > [...] > > > > > > it's about consistency with what the kernel types mean. When > > > > > > some checker detects your using little endian operations on a > > > > > > big endian structure (like in the prink for instance) they're > > > > > > going to keep emailing you about it. > > > > > > > > > > As mentioned above, using different terminology is meant to cause > > > > > more confusion than just difference in endianness which is > > > > > manageable inside TEE. > > > > > > > > > > And I think it's safe to say that the kernel implements UUID in > > > > > big endian format and thus uses %pUb whereas OP-TEE implements > > > > > UUID in little endian format and thus uses %pUl. > > > > > > > > So what I think you're saying is that if we still had uuid_be and > > > > uuid_le you'd use uuid_le, because that's exactly the structure > > > > described in the docs. But because we renamed > > > > > > > > uuid_be -> uuid_t > > > > uuid_le -> guid_t > > > > > > > > You can't use guid_t as a kernel type because it has the wrong > > > > name? > > > > > > Isn't the rename commit description [1] pretty clear about which is > > > the true UUID type from Linux point of view? > > > > I don't think the kernel code takes a position on eternal verity, just > > on logical or arithmetic truth. We just have to deal with both LE and > > BE UUIDs so we have appropriate types for them and the LE type is now > > named guid_t. They're both equally correct to use provided the use > > case matches the designed one. So does the name really matter? > > Yes it does. I guess I have provided enough reasoning for that. Also, > the rename commit itself illustrates its importance and clarifies the > use case for which they are meant to be used. > > > If we > > did > > > > #define uuid_le_t guid_t > > > > would you be happy? (not that the kernel cares about karmic emotional > > states either ...) > > It's not about me being happy but more about confusion and > inconsistency it will bring. > > IMO, either kernel should be opinionated about UUID endianness like > currently it is: > > uuid_t and its corresponding helpers (eg. UUID_INIT) follows BE format. > > or support both endianness for UUID (no common type: uuid_t) like we > had earlier prior to rename commit: > > uuid_be_t and its corresponding helpers (eg. UUID_BE_INIT) follow BE format. > uuid_le_t and its corresponding helpers (eg. UUID_LE_INIT) follow LE format. > > But even if we consider later case as well, I am still not sure if we > can switch to uuid_le_t as it's been part of TEE core ABI > (open_session) where UUID is passed in BE format (see LE to BE > conversion in TEE client [1] and vice-versa in OP-TEE OS [2]) and > won't be a backwards compatible change. > > [1] https://github.com/OP-TEE/optee_client/blob/master/libteec/src/tee_client_api.c#L595 > [2] https://github.com/OP-TEE/optee_os/blob/master/core/arch/arm/kernel/ree_fs_ta.c#L92 I'm struck that all references here are to code that does not run in kernel space. Frankly on LKML I don't know if we should even *care* what format UUIDs are stored in other address spaces. We care about is the endianness of the UUID on the interface boundaries into and out of the kernel[1] and we care that we use the correct kernel type to describe it. I understood from Jerome's post that the UUID that the kernel manipulates are, in fact, big endian and that they should be called uuid_t. Is there more going on here or is that it? Daniel. [1] I guess we'd also like those interface boundaries to be reasonably sane but if they already exist and are the interface is consistent about endianness then I find it hard to see no reason for a gratuitous endianness change.