Hi Andrew,
While your suggestions look interesting, I am afraid they are not particularly
what we want to cover with this discussion at the moment.
Making assertions go through DEBUG printing functions/macros is what we have to
strongly disagree about. Assertions and debug prints are separate things
configurable by separate PCDs. We should not mix them. Introducing constraint
assertions is a logical step forward in understanding that different software
works in different environments.
- There are normal, or, as I call them, invariant assertions (e.g.
preconditions), for places where the function cannot work unless the assertion
is satisfied. This is where we ASSERT.
- There are constraint assertions, which signalise that bad data came through
the function, even though the function was called from a trusted source. This
is where we call CONSTRAINT_ASSERT.
The thing we need is to have the latter separable and configurable, because not
every piece of software works in a trusted environment. Other than that,
constraint assertions, when enabled, are not anyhow different from normal
assertions in the sense of action taken. Assertions have configurable
breakpoints and deadloops, and DEBUG prints go through a different route in
DebugLib that may cause entirely different effects. For example, we halt
execution upon printing to DEBUG_ERROR in our DebugLib even in release builds.
To make it clear, currently I plan to add the following interface:
#define CONSTRAINT_ASSERT(Expression) \
do { \
if (DebugConstraintAssertEnabled ()) { \
if (!(Expression)) { \
_ASSERT (Expression); \
ANALYZER_UNREACHABLE (); \
} \
} \
} while (FALSE)
with DebugConstraintAssertEnabled implemented as
(BOOLEAN) ((PcdGet8(PcdDebugPropertyMask) & DEBUG_PROPERTY_DEBUG_ASSERT_ENABLED
| DEBUG_PROPERTY_CONTRAINT_ASSERT_DISABLED) ==
DEBUG_PROPERTY_DEBUG_ASSERT_ENABLED)
Your suggestion with require macros looks interesting indeed, but I believe it
is in fact parallel to this discussion. The change we discuss introduces a new
assertion primitive — constraint assertions, while REQUIRE macros are mostly
about advanced syntax sugar and higher level assertion primitives on top of
existing ones. Perhaps we can have this and make a good use of it, especially
given that it brought some practical benefit in Apple, but I would rather
discuss this later once constraint assertions are merged into EDK II tree.
Best wishes,
Vitaly
On Sat, Feb 15, 2020 at 03:02, Andrew Fish <af...@apple.com> wrote:
>> On Feb 14, 2020, at 2:50 PM, Michael D Kinney <michael.d.kin...@intel.com>
>> wrote:
>>
>> Hi Vitaly,
>>
>> I agree that this proposal makes a lot of sense. We recently added a new
>> assert type called STATIC_ASSERT() for assert conditions that can be tested
>> at build time.
>>
>> A new assert type for checks that can be removed and the API still
>> guarantees that it fails gracefully with a proper return code is a good
>> idea. Given we have STATIC_ASSERT(), how about naming the new macro
>> CONSTRAINT_ASSERT()?
>>
>> We also want the default to be enabled. The current use of bit 0x40 in
>> PcdDebugPropertyMask is always clear, so we want the asserts enabled when
>> 0x40 is clear. We can change the name of the define bit to
>> DEBUG_PROPERTY_CONTRAINT_ASSERT_DISABLED so bit 0x40 needs to be set in
>> PcdDebugPropertyMask to disable these types of asserts.
>>
>> This approach does require all the DebugLib implementations to be updated
>> with the new DebugConstraintAssertDisabled() API.
>
> Mike,
>
> If you wanted to be backward compatible you could just use DebugAssertEnabled
> () but in place of _ASSERT() use _CONSTRAINT_ASSERT
>
> #define _ASSERT(Expression) DebugAssert (__FILE__, __LINE__, #Expression)
>
> #define _CONSTRAINT_ASSERT(Expression) DebugPrint (DEBUG_ERROR, "ASSERT
> %a(%d): %a\n",, __FILE__, __LINE__, #Expression)
>
> Not as elegant as the non backward compatible change, but I thought I'd throw
> it out there.
>
> There are some ancient Apple C ASSERT macros [AssertMacros.h] that also have
> the concept of require. Require includes an exception label (goto label). It
> is like a CONSTRAINT_ASSERT() but with the label. On release builds the DEBUG
> prints are skipped.
>
> So we could do something like:
>
> EFI_STATUS Status = EFI_INVALID_PARAMETER;
>
> REQUIRE(Arg1 != NULL, ErrorExit);
> REQUIRE(Arg2 != NULL, ErrorExit);
> REQUIRE(Arg3 != NULL, ErrorExit);
>
> ErrorExit:
> return Status;
>
> There is another form that allows an ACTION (a statement to execute. So you
> could have:
>
> EFI_STATUS Status;
>
> REQUIRE_ACTION(Arg1 != NULL, ErrorExit, Status = EFI_INVALID_PARAMETER);
> REQUIRE_ACTION(Arg2 != NULL, ErrorExit, Status = EFI_INVALID_PARAMETER);
> REQUIRE_ACTION(Arg3 != NULL, ErrorExit, Status = EFI_INVALID_PARAMETER);
>
> ErrorExit:
> return Status;
>
> If you use CONSTRAINT_ASSERT();
>
> if (Arg1 == NULL || Arg2 == NULL || Arg3 == NULL) {
> CONSTRAINT_ASSERT (Arg1 != NULL);
> CONSTRAINT_ASSERT (Arg2 != NULL);
> CONSTRAINT_ASSERT (Arg3 != NULL);
> return EFI_INVALID_PARAMETER;
> }
>
> I'd note error processing args on entry is the simplest case. In a more
> complex case when cleanup is required the goto label is more useful.
>
> I guess we could argue for less typing and more symmetry and say use ASSERT,
> CONSTRAINT, and REQUIRE. I guess you could add an ASSERT_ACTION too.
>
> The AssertMacros.h versions also support _quiet (skip the print) and _string
> (add a string to the print) so you end up with:
> REQUIRE
> REQUIRE_STRING
>
> REQUIRE_QUIET
>
> REQUIRE_ACTION
>
> REQUIRE_ACTION_STRING
>
> REQUIRE_ACTION_QUIET
>
> We could also end up with
> CONSTRAINT
> CONSTRAINT_STRING
>
> CONSTRAINT_QUIET
>
> I think the main idea behind _QUIET is you can silence things that are too
> noisy, and you can easily make noise things show up by removing the _QUIET to
> debug.
>
> I'd thought I throw out the other forms for folks to think about. I'm
> probably biased as I used to looking at code and seeing things like
> require_action_string(Arg1 != NULL, ErrorExit, Status =
> EFI_INVALID_PARAMETER, "1st Arg1 check");
>
> Thanks,
>
> Andrew Fish
>
> PS The old debug macros had 2 versions of CONSTRAINT check and verify. The
> check version was compiled out on a release build, the verify version always
> does the check and just skips the DEBUG print.
>
>> Mike
>>
>> From: vit9696 <vit9...@protonmail.com>
>> Sent: Friday, February 14, 2020 9:38 AM
>> To: Kinney, Michael D <michael.d.kin...@intel.com>
>> Cc: devel@edk2.groups.io; Gao, Liming <liming....@intel.com>; Gao, Zhichao
>> <zhichao....@intel.com>; Marvin Häuser <marvin.haeu...@outlook.com>; Laszlo
>> Ersek <ler...@redhat.com>
>> Subject: Re: [edk2-devel] [PATCH v3 0/1] Add PCD to disable safe string
>> constraint assertions
>>
>> Michael,
>>
>> Generalising the approach makes good sense to me, but we need to make an
>> obvious distinguishable difference between:
>> - precondition and invariant assertions (i.e. assertions, where function
>> will NOT work if they are violated)
>> - constraint asserts (i.e. assertions, which allow us to spot unintentional
>> behaviour when parsing untrusted data, but which do not break function
>> behaviour).
>>
>> As we want to use this outside of SafeString, I suggest the following:
>> - Introduce DEBUG_PROPERTY_ASSERT_CONSTRAINT_ENABLED 0x40 bit for
>> PcdDebugPropertyMask instead of PcdAssertOnSafeStringConstraints.
>> - Introduce DebugAssertConstraintEnabled DebugLib function to check for
>> DEBUG_PROPERTY_ASSERT_CONSTRAINT_ENABLED.
>> - Introduce ASSERT_CONSTRAINT macro, that will assert only if
>> DebugConstraintAssertEnabled returns true.
>> - Change SafeString ASSERTS in SAFE_STRING_CONSTRAINT_CHECK to
>> ASSERT_CONSTRAINTs.
>> - Use ASSERT_CONSTRAINT in other places where necessary.
>>
>> I believe this way lines best with EDK II design. If there are no
>> objections, I can submit the patch in the beginning of next week.
>>
>> Best wishes,
>> Vitaly
>>
>>> 14 февр. 2020 г., в 20:00, Kinney, Michael D <michael.d.kin...@intel.com>
>>> написал(а):
>>>
>>> Vitaly,
>>>
>>> I want to make sure a feature PCD can be used to disable ASSERT() behavior
>>> in more than just safe string functions in BaseLib.
>>>
>>> Can we consider changing the name and description of
>>> PcdAssertOnSafeStringConstraints to be more generic, so if we find other
>>> lib APIs, the name will make sense?
>>>
>>> Maybe something like: PcdEnableLibraryAssertChecks? Default is TRUE. Can
>>> set to FALSE in DSC file to disable ASSERT() checks.
>>>
>>> Thanks,
>>>
>>> Mike
>>>
>>> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Vitaly
>>> Cheptsov via Groups.Io
>>> Sent: Friday, February 14, 2020 3:55 AM
>>> To: Kinney, Michael D <michael.d.kin...@intel.com>; Gao, Liming
>>> <liming....@intel.com>; Gao, Zhichao <zhichao....@intel.com>;
>>> devel@edk2.groups.io
>>> Cc: Marvin Häuser <marvin.haeu...@outlook.com>; Laszlo Ersek
>>> <ler...@redhat.com>
>>> Subject: Re: [edk2-devel] [PATCH v3 0/1] Add PCD to disable safe string
>>> constraint assertions
>>>
>>> Replying as per Liming's request for this to be merged into
>>> edk2-stable202002.
>>>
>>> On Mon, Feb 10, 2020 at 14:12, vit9696 <vit9...@protonmail.com> wrote:
>>>
>>>> Hello,
>>>>
>>>> It has been quite some time since we submitted the patch with so far no
>>>> negative response. As I mentioned previously, my team will strongly
>>>> benefit from its landing in EDK II mainline. Since it does not add any
>>>> regressions and can be viewed as a feature implementation for the rest of
>>>> EDK II users, I request this to be merged upstream in edk2-stable202002.
>>>>
>>>> Best wishes,
>>>> Vitaly
>>>>
>>>>> 27 янв. 2020 г., в 12:47, vit9696 <vit9...@protonmail.com> написал(а):
>>>>>
>>>>>
>>>>> Hi Mike,
>>>>>
>>>>> Any progress with this? We would really benefit from this landing in the
>>>>> next stable release.
>>>>>
>>>>> Best,
>>>>> Vitaly
>>>>>
>>>>>> 8 янв. 2020 г., в 19:35, Kinney, Michael D <michael.d.kin...@intel.com>
>>>>>> написал(а):
>>>>>>
>>>>>>
>>>>>> Hi Vitaly,
>>>>>>
>>>>>> Thanks for the additional background. I would like
>>>>>> a couple extra day to review the PCD name and the places
>>>>>> the PCD might potentially be used.
>>>>>>
>>>>>> If we find other APIs where ASSERT() behavior is only
>>>>>> valuable during dev/debug to quickly identify misuse
>>>>>> with trusted data and the API provides predicable
>>>>>> return behavior when ASSERT() is disabled, then I would
>>>>>> like to have a pattern we can potentially apply to all
>>>>>> these APIs across all packages.
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>> Mike
>>>>>>
>>>>>>> -----Original Message-----
>>>>>>> From: devel@edk2.groups.io <devel@edk2.groups.io> On
>>>>>>> Behalf Of Vitaly Cheptsov via Groups.Io
>>>>>>> Sent: Monday, January 6, 2020 10:44 AM
>>>>>>> To: Kinney, Michael D <michael.d.kin...@intel.com>
>>>>>>> Cc: devel@edk2.groups.io
>>>>>>> Subject: Re: [edk2-devel] [PATCH v3 0/1] Add PCD to
>>>>>>> disable safe string constraint assertions
>>>>>>>
>>>>>>> Hi Mike,
>>>>>>>
>>>>>>> Yes, the primary use case is for UEFI Applications. We
>>>>>>> do not want to disable ASSERT’s completely, as
>>>>>>> assertions that make sense, i.e. the ones signalising
>>>>>>> about interface misuse, are helpful for debugging.
>>>>>>>
>>>>>>> I have already explained in the BZ that basically all
>>>>>>> safe string constraint assertions make no sense for
>>>>>>> handling untrusted data. We find this use case very
>>>>>>> logical, as these functions behave properly with
>>>>>>> assertions disabled and cover all these error
>>>>>>> conditions by the return statuses. In such situation is
>>>>>>> not useful for these functions to assert, as we end up
>>>>>>> inefficiently reimplementing the logic. I would have
>>>>>>> liked the approach of discussing the interfaces
>>>>>>> individually, but I struggle to find any that makes
>>>>>>> sense from this point of view.
>>>>>>>
>>>>>>> AsciiStrToGuid will ASSERT when the length of the
>>>>>>> passed string is odd. Functions that cannot, ahem,
>>>>>>> parse, for us are pretty much useless.
>>>>>>> AsciiStrCatS will ASSERT when the appended string does
>>>>>>> not fit the buffer. For us this logic makes this
>>>>>>> function pretty much equivalent to deprecated and thus
>>>>>>> unavailable AsciiStrCat, except it is also slower.
>>>>>>>
>>>>>>> My original suggestion was to remove the assertions
>>>>>>> entirely, but several people here said that they use
>>>>>>> them to verify usage errors when handling trusted data.
>>>>>>> This makes good sense to me, so we suggest to support
>>>>>>> both cases by introducing a PCD in this patch.
>>>>>>>
>>>>>>> Best wishes,
>>>>>>> Vitaly
>>>>>>>
>>>>>>>> 6 янв. 2020 г., в 21:28, Kinney, Michael D
>>>>>>> <michael.d.kin...@intel.com> написал(а):
>>>>>>>>
>>>>>>>>
>>>>>>>> Hi Vitaly,
>>>>>>>>
>>>>>>>> Is the use case for UEFI Applications?
>>>>>>>>
>>>>>>>> There is a different mechanism to disable all
>>>>>>> ASSERT()
>>>>>>>> statements within a UEFI Application.
>>>>>>>>
>>>>>>>> If a component is consuming data from an untrusted
>>>>>>> source,
>>>>>>>> then that component is required to verify the
>>>>>>> untrusted
>>>>>>>> data before passing it to a function that clearly
>>>>>>> documents
>>>>>>>> is input requirements. If this approach is followed,
>>>>>>> then
>>>>>>>> the BaseLib functions can be used "as is" as long as
>>>>>>> the
>>>>>>>> ASSERT() conditions are verified before calling.
>>>>>>>>
>>>>>>>> If there are some APIs that currently document their
>>>>>>> ASSERT()
>>>>>>>> behavior and we think that ASSERT() behavior is
>>>>>>> incorrect and
>>>>>>>> should be handled by an existing error return value,
>>>>>>> then we
>>>>>>>> should discuss each of those APIs individually.
>>>>>>>>
>>>>>>>> Mike
>>>>>>>>
>>>>>>>>
>>>>>>>>> -----Original Message-----
>>>>>>>>> From: devel@edk2.groups.io <devel@edk2.groups.io> On
>>>>>>>>> Behalf Of Vitaly Cheptsov via Groups.Io
>>>>>>>>> Sent: Friday, January 3, 2020 9:13 AM
>>>>>>>>> To: devel@edk2.groups.io
>>>>>>>>> Subject: [edk2-devel] [PATCH v3 0/1] Add PCD to
>>>>>>> disable
>>>>>>>>> safe string constraint assertions
>>>>>>>>>
>>>>>>>>> REF:
>>>>>>>>> https://bugzilla.tianocore.org/show_bug.cgi?id=2054
>>>>>>>>>
>>>>>>>>> Requesting for merge in edk2-stable202002.
>>>>>>>>>
>>>>>>>>> Changes since V1:
>>>>>>>>> - Enable assertions by default to preserve the
>>>>>>> original
>>>>>>>>> behaviour
>>>>>>>>> - Fix bugzilla reference link
>>>>>>>>> - Update documentation in BaseLib.h
>>>>>>>>>
>>>>>>>>> Vitaly Cheptsov (1):
>>>>>>>>> MdePkg: Add PCD to disable safe string constraint
>>>>>>>>> assertions
>>>>>>>>>
>>>>>>>>> MdePkg/MdePkg.dec | 6 ++
>>>>>>>>> MdePkg/Library/BaseLib/BaseLib.inf | 11 +--
>>>>>>>>> MdePkg/Include/Library/BaseLib.h | 74
>>>>>>>>> +++++++++++++-------
>>>>>>>>> MdePkg/Library/BaseLib/SafeString.c | 4 +-
>>>>>>>>> MdePkg/MdePkg.uni | 6 ++
>>>>>>>>> 5 files changed, 71 insertions(+), 30 deletions(-)
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>> 2.21.0 (Apple Git-122.2)
>>>>>>>>>
>>>>>>>>>
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>>>>>>
>>>>>
>>
>>
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