DPDK patches and discussions
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From: Thomas Monjalon <thomas@monjalon.net>
To: David Marchand <david.marchand@redhat.com>,
	nhorman@tuxdriver.com, bluca@debian.org, ktraynor@redhat.com,
	Ray Kinsella <mdr@ashroe.eu>
Cc: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
	Akhil Goyal <akhil.goyal@nxp.com>,
	"Trahe, Fiona" <fiona.trahe@intel.com>,
	Ferruh Yigit <ferruh.yigit@intel.com>,
	dev@dpdk.org, Anoob Joseph <anoobj@marvell.com>,
	"Kusztal, ArkadiuszX" <arkadiuszx.kusztal@intel.com>,
	"Richardson, Bruce" <bruce.richardson@intel.com>,
	"Mcnamara, John" <john.mcnamara@intel.com>,
	dodji@seketeli.net, Andrew Rybchenko <arybchenko@solarflare.com>,
	aconole@redhat.com
Subject: Re: [dpdk-dev] [PATCH v2 4/4] add ABI checks
Date: Mon, 03 Feb 2020 22:07:22 +0100
Message-ID: <2546229.NgBsaNRSFp@xps> (raw)
In-Reply-To: <4ed777ce-8320-4636-2c9c-62bb96b66392@ashroe.eu>

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




  reply index

Thread overview: 104+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-20 15:20 [dpdk-dev] [PATCH] " David Marchand
2019-12-20 15:32 ` Richardson, Bruce
2019-12-20 16:20   ` Kinsella, Ray
2019-12-20 21:00     ` Thomas Monjalon
2020-01-06 13:17       ` Aaron Conole
2020-01-15 13:07         ` Burakov, Anatoly
2020-01-14 23:19     ` Thomas Monjalon
2020-01-15 11:33       ` Neil Horman
2020-01-15 12:38         ` Thomas Monjalon
2020-01-16 11:52           ` Neil Horman
2020-01-16 14:20             ` Thomas Monjalon
2020-01-16 18:49               ` Neil Horman
2020-01-16 20:01                 ` Thomas Monjalon
2020-01-17 19:01                   ` Neil Horman
2020-01-17 21:26                     ` David Marchand
2019-12-20 20:25 ` Neil Horman
2020-01-29 17:26 ` [dpdk-dev] [PATCH v2 0/4] " David Marchand
2020-01-29 17:26   ` [dpdk-dev] [PATCH v2 1/4] hash: fix meson headers packaging David Marchand
2020-01-30 10:12     ` Luca Boccassi
2020-01-30 10:54       ` David Marchand
2020-01-30 10:56         ` Luca Boccassi
2020-01-29 17:26   ` [dpdk-dev] [PATCH v2 2/4] build: split build helper David Marchand
2020-01-29 17:26   ` [dpdk-dev] [PATCH v2 3/4] build: test meson installation David Marchand
2020-01-29 17:26   ` [dpdk-dev] [PATCH v2 4/4] add ABI checks David Marchand
2020-01-29 17:42     ` Thomas Monjalon
2020-01-29 18:10       ` Anoob Joseph
2020-01-29 20:03         ` David Marchand
2020-01-29 20:13           ` Akhil Goyal
2020-01-30 16:09             ` Ferruh Yigit
2020-01-30 20:18               ` Thomas Monjalon
2020-01-31  9:03                 ` Ferruh Yigit
2020-01-31 10:26                   ` Ananyev, Konstantin
2020-01-31 14:16                 ` Trahe, Fiona
2020-02-02 13:05                   ` Thomas Monjalon
2020-02-02 14:41                     ` Ananyev, Konstantin
2020-02-03  9:30                       ` Ferruh Yigit
2020-02-03 11:50                         ` Neil Horman
2020-02-03 13:09                           ` Ferruh Yigit
2020-02-03 14:00                             ` Dodji Seketeli
2020-02-03 14:46                               ` Ferruh Yigit
2020-02-03 15:08                             ` Trahe, Fiona
2020-02-03 17:09                         ` Thomas Monjalon
2020-02-03 17:34                           ` Thomas Monjalon
2020-02-03 18:55                             ` Ray Kinsella
2020-02-03 21:07                               ` Thomas Monjalon [this message]
2020-02-04  9:46                                 ` Ferruh Yigit
2020-02-04 10:24                                 ` Thomas Monjalon
2020-02-04 12:44                                   ` Trahe, Fiona
2020-02-04 15:52                                     ` Trahe, Fiona
2020-02-04 15:59                                       ` Thomas Monjalon
2020-02-04 17:46                                         ` Trahe, Fiona
2020-02-13 14:51                                           ` Kusztal, ArkadiuszX
2020-03-16 12:57                                             ` Trahe, Fiona
2020-03-16 13:09                                               ` Thomas Monjalon
2020-03-17 13:27                                                 ` Kusztal, ArkadiuszX
2020-03-17 15:10                                                   ` Thomas Monjalon
2020-03-17 19:10                                                     ` Kusztal, ArkadiuszX
2020-02-04 12:57                                   ` Kevin Traynor
2020-02-04 14:44                                   ` Aaron Conole
2020-02-04 19:49                                     ` Neil Horman
2020-02-04  9:51                               ` David Marchand
2020-02-04 10:10                                 ` Trahe, Fiona
2020-02-04 10:38                                   ` Thomas Monjalon
2020-02-05 11:10                                 ` Ray Kinsella
2020-02-03 17:40                           ` Ferruh Yigit
2020-02-03 18:40                             ` Thomas Monjalon
2020-02-04  9:19                               ` Ferruh Yigit
2020-02-04  9:45                                 ` Thomas Monjalon
2020-02-04  9:56                                   ` Ferruh Yigit
2020-02-04 10:08                                     ` Bruce Richardson
2020-02-04 10:17                                     ` Kevin Traynor
2020-02-04 10:16                             ` Akhil Goyal
2020-02-04 10:28                               ` Thomas Monjalon
2020-02-04 10:32                                 ` Akhil Goyal
2020-02-04 11:35                                   ` Bruce Richardson
2020-02-04 22:10                                   ` Neil Horman
2020-02-05  6:16                                     ` [dpdk-dev] [EXT] " Anoob Joseph
2020-02-05 14:33                                       ` Trahe, Fiona
2020-02-04 21:59                               ` [dpdk-dev] " Neil Horman
2020-01-30 13:06         ` Trahe, Fiona
2020-01-30 15:59           ` Thomas Monjalon
2020-01-30 16:42             ` Ferruh Yigit
2020-01-30 23:49             ` Ananyev, Konstantin
2020-01-31  9:07               ` Ferruh Yigit
2020-01-31  9:37                 ` Ananyev, Konstantin
2020-01-30 10:57   ` [dpdk-dev] [PATCH v2 0/4] " Luca Boccassi
2020-01-30 16:00 ` [dpdk-dev] [PATCH v3 " David Marchand
2020-01-30 16:00   ` [dpdk-dev] [PATCH v3 1/4] hash: fix meson headers packaging David Marchand
2020-01-30 18:01     ` Wang, Yipeng1
2020-01-30 18:40       ` Honnappa Nagarahalli
2020-02-05 19:51         ` Wang, Yipeng1
2020-01-30 16:00   ` [dpdk-dev] [PATCH v3 2/4] build: split build helper David Marchand
2020-01-30 16:00   ` [dpdk-dev] [PATCH v3 3/4] build: test meson installation David Marchand
2020-01-30 22:17     ` Thomas Monjalon
2020-01-30 16:00   ` [dpdk-dev] [PATCH v3 4/4] add ABI checks David Marchand
2020-01-30 22:32     ` Thomas Monjalon
2020-02-01 15:29       ` David Marchand
2020-01-30 22:44     ` Thomas Monjalon
2020-02-02 21:08 ` [dpdk-dev] [PATCH v4 0/3] " David Marchand
2020-02-02 21:08   ` [dpdk-dev] [PATCH v4 1/3] hash: fix meson headers packaging David Marchand
2020-02-05 19:53     ` Wang, Yipeng1
2020-02-02 21:08   ` [dpdk-dev] [PATCH v4 2/3] build: split build helper David Marchand
2020-02-02 21:08   ` [dpdk-dev] [PATCH v4 3/3] add ABI checks David Marchand
2020-02-05 14:13   ` [dpdk-dev] [PATCH v4 0/3] " Thomas Monjalon

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