On 2/3/2020 9:07 PM, Thomas Monjalon wrote:

03/02/2020 19:55, Ray Kinsella:

quoted

On 03/02/2020 17:34, Thomas Monjalon wrote:

quoted

03/02/2020 18:09, Thomas Monjalon:

quoted

03/02/2020 10:30, Ferruh Yigit:

quoted

On 2/2/2020 2:41 PM, Ananyev, Konstantin wrote:

quoted

02/02/2020 14:05, Thomas Monjalon:

quoted

31/01/2020 15:16, Trahe, Fiona:

quoted

On 1/30/2020 8:18 PM, Thomas Monjalon wrote:

quoted

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.

quoted

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.

quoted

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.

quoted

	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.
"

quoted

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].

quoted

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.

quoted

quoted

quoted

- _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.

We can remove LIST_END only if we go with option (c).

Two different approach,
- Provide the LIST_END and expect application protect itself against new values
can be coming in newer version of the library
- Do ABI versioning to prevent application receive new values at all, (c).

We can select one, but I believe the selection shouldn't be based on just
silencing the ABI check tool.

quoted

quoted

quoted

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