Thomas Monjalon <tho...@monjalon.net> writes: > RED FLAG > > I don't see a lot of reactions, so I summarize the issue. > We need action TODAY! > > API makes think that rte_cryptodev_info_get() cannot return > a value >= 3 (RTE_CRYPTO_AEAD_LIST_END in 19.11). > Current 20.02 returns 3 (RTE_CRYPTO_AEAD_CHACHA20_POLY1305). > The ABI compatibility contract is broken currently. > > There are 3 possible outcomes: > > a) Change the API comments and backport to 19.11.1 > The details are discussed between Ferruh and me. > Either put responsibility on API user (with explicit comment), > or expose ABI extension allowance with a new API max value. > In both cases, this is breaking the implicit contract of 19.11.0. > This option can be chosen only if release and ABI maintainers > vote for it. > > b) Revert Chacha-Poly from 20.02-rc2. > > c) Add versioned function rte_cryptodev_info_get_v1911() > which calls rte_cryptodev_info_get() and filters out > RTE_CRYPTO_AEAD_CHACHA20_POLY1305 capability. > So Chacha-Poly capability would be seen and usable only > if compiling with DPDK 20.02. > > I hope it is clear what are the actions for everybody: > - ABI and release maintainers must say yes or no to the proposal (a) > - In the meantime, crypto team must send a patch for the proposal (c) > - If (a) and (c) are not possible at the end of today, I will take (b) > > Note: do not say it is too short for (c), as it was possible to work > on such solution since the issue was exposed on last Wednesday.
While I'm not a maintainer, if I my opinion counts for anything, I'd choose option c or b. Absolutely NACK to a. > > 03/02/2020 22:07, Thomas Monjalon: >> 03/02/2020 19:55, Ray Kinsella: >> > On 03/02/2020 17:34, Thomas Monjalon wrote: >> > > 03/02/2020 18:09, Thomas Monjalon: >> > >> 03/02/2020 10:30, Ferruh Yigit: >> > >>> On 2/2/2020 2:41 PM, Ananyev, Konstantin wrote: >> > >>>> 02/02/2020 14:05, Thomas Monjalon: >> > >>>>> 31/01/2020 15:16, Trahe, Fiona: >> > >>>>>> On 1/30/2020 8:18 PM, Thomas Monjalon wrote: >> > >>>>>>> If library give higher value than expected by the application, >> > >>>>>>> if the application uses this value as array index, >> > >>>>>>> there can be an access out of bounds. >> > >>>>>> >> > >>>>>> [Fiona] All asymmetric APIs are experimental so above shouldn't be >> > >>>>>> a problem. >> > >>>>>> But for the same issue with sym crypto below, I believe Ferruh's >> > >>>>>> explanation makes >> > >>>>>> sense and I don't see how there can be an API breakage. >> > >>>>>> So if an application hasn't compiled against the new lib it >> > >>>>>> will be still using the old value >> > >>>>>> which will be within bounds. If it's picking up the higher >> > >>>>>> new value from the lib it must >> > >>>>>> have been compiled against the lib so shouldn't have problems. >> > >>>>> >> > >>>>> You say there is no ABI issue because the application will be >> > >>>>> re-compiled >> > >>>>> for the updated library. Indeed, compilation fixes compatibility >> > >>>>> issues. >> > >>>>> But this is not relevant for ABI compatibility. >> > >>>>> ABI compatibility means we can upgrade the library without >> > >>>>> recompiling >> > >>>>> the application and it must work. >> > >>>>> You think it is a false positive because you assume the application >> > >>>>> "picks" the new value. I think you miss the case where the new value >> > >>>>> is returned by a function in the upgraded library. >> > >>>>> >> > >>>>>> There are also no structs on the API which contain arrays using this >> > >>>>>> for sizing, so I don't see an opportunity for an appl to have a >> > >>>>>> mismatch in memory addresses. >> > >>>>> >> > >>>>> Let me demonstrate where the API may "use" the new value >> > >>>>> RTE_CRYPTO_AEAD_CHACHA20_POLY1305 and how it impacts the application. >> > >>>>> >> > >>>>> Once upon a time a DPDK application counting the number of devices >> > >>>>> supporting each AEAD algo (in order to find the best supported algo). >> > >>>>> It is done in an array indexed by algo id: >> > >>>>> int aead_dev_count[RTE_CRYPTO_AEAD_LIST_END]; >> > >>>>> The application is compiled with DPDK 19.11, >> > >>>>> where RTE_CRYPTO_AEAD_LIST_END = 3. >> > >>>>> So the size of the application array aead_dev_count is 3. >> > >>>>> This binary is run with DPDK 20.02, >> > >>>>> where RTE_CRYPTO_AEAD_CHACHA20_POLY1305 = 3. >> > >>>>> When calling rte_cryptodev_info_get() on a device QAT_GEN3, >> > >>>>> rte_cryptodev_info.capabilities.sym.aead.algo is set to >> > >>>>> RTE_CRYPTO_AEAD_CHACHA20_POLY1305 (= 3). >> > >>>>> The application uses this value: >> > >>>>> ++ aead_dev_count[info.capabilities.sym.aead.algo]; >> > >>>>> The application is crashing because of out of bound access. >> > >>>> >> > >>>> I'd say this is an example of bad written app. >> > >>>> It probably should check that returned by library value doesn't >> > >>>> exceed its internal array size. >> > >>> >> > >>> +1 >> > >>> >> > >>> Application should ignore values >= MAX. >> > >> >> > >> Of course, blaming the API user is a lot easier than looking at the API. >> > >> Here the API has RTE_CRYPTO_AEAD_LIST_END which can be understood >> > >> as the max value for the application. >> > >> Value ranges are part of the ABI compatibility contract. >> > >> It seems you expect the application developer to be aware that >> > >> DPDK could return a higher value, so the application should >> > >> check every enum values after calling an API. CRAZY. >> > >> >> > >> When we decide to announce an ABI compatibility and do some marketing, >> > >> everyone is OK. But when we need to really make our ABI compatible, >> > >> I see little or no effort. DISAPPOINTING. >> > >> >> > >>> Do you suggest we don't extend any enum or define between ABI breakage >> > >>> releases >> > >>> to be sure bad written applications not affected? >> > >> >> > >> I suggest we must consider not breaking any assumption made on the API. >> > >> Here we are breaking the enum range because nothing mentions _LIST_END >> > >> is not really the absolute end of the enum. >> > >> The solution is to make the change below in 20.02 + backport in 19.11.1: >> > > >> > > Thinking twice, merging such change before 20.11 is breaking the >> > > ABI assumption based on the API 19.11.0. >> > > I ask the release maintainers (Luca, Kevin, David and me) and >> > > the ABI maintainers (Neil and Ray) to vote for a or b solution: >> > > a) add comment and LIST_MAX as below in 20.02 + 19.11.1 >> > >> > That would still be an ABI breakage though right. >> > >> > > b) wait 20.11 and revert Chacha-Poly from 20.02 >> > >> > Thanks for analysis above Fiona, Ferruh and all. >> > >> > That is a nasty one alright - there is no "good" answer here. >> > I agree with Ferruh's sentiments overall, we should rethink this API for >> > 20.11. >> > Could do without an enumeration? >> > >> > There a c) though right. >> > We could work around the issue by api versioning rte_cryptodev_info_get() >> > and friends. >> > So they only support/acknowledge the existence of Chacha-Poly for >> > applications build against > 20.02. >> >> I agree there is a c) as I proposed in another email: >> http://mails.dpdk.org/archives/dev/2020-February/156919.html >> " >> In this case, the proper solution is to implement >> rte_cryptodev_info_get_v1911() so it filters out >> RTE_CRYPTO_AEAD_CHACHA20_POLY1305 capability. >> With this solution, an application compiled with DPDK 19.11 will keep >> seeing the same range as before, while a 20.02 application could >> see and use ChachaPoly. >> " >> >> > It would be painful I know. >> >> Not so painful in my opinion. >> Just need to call rte_cryptodev_info_get() from >> rte_cryptodev_info_get_v1911() and filter the value >> in the 19.11 range: [0..AES_GCM]. >> >> > It would also mean that Chacha-Poly would only be available to >> > those building against >= 20.02. >> >> Yes exactly. >> >> The addition of comments and LIST_MAX like below are still valid >> to avoid versioning after 20.11. >> >> > >> - _LIST_END >> > >> + _LIST_END, /* an ABI-compatible version may increase this value */ >> > >> + _LIST_MAX = _LIST_END + 42 /* room for ABI-compatible additions */ >> > >> }; >> > >> >> > >> Then *_LIST_END values could be ignored by libabigail with such a >> > >> change. >> >> In order to avoid ABI check complaining, the best is to completely >> remove LIST_END in DPDK 20.11. >> >> >> > >> If such a patch is not done by tomorrow, I will have to revert >> > >> Chacha-Poly commits before 20.02-rc2, because >> > >> >> > >> 1/ LIST_END, without any comment, means "size of range" >> > >> 2/ we do not blame users for undocumented ABI changes >> > >> 3/ we respect the ABI compatibility contract
