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
