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From: Ray Kinsella <mdr@ashroe.eu>
To: Thomas Monjalon <thomas@monjalon.net>,
	David Marchand <david.marchand@redhat.com>,
	nhorman@tuxdriver.com, bluca@debian.org, ktraynor@redhat.com
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, 3 Feb 2020 18:55:59 +0000	[thread overview]
Message-ID: <4ed777ce-8320-4636-2c9c-62bb96b66392@ashroe.eu> (raw)
In-Reply-To: <2336620.usQuhbGJ8B@xps>



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.

It would be painful I know.
It would also mean that Chacha-Poly would only be available to those building against >= 20.02.


> 
> 
>> - _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.
>>
>> 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	other threads:[~2020-02-03 18:56 UTC|newest]

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 [this message]
2020-02-03 21:07                               ` Thomas Monjalon
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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