Re: [edk2-devel] [PATCH v1 1/1] MdePkg: Add PCD to disable safe string constraint assertions

["Yao, Jiewen" <jiewen.yao@intel.com>]

Hi Vitaly
We have discussed the ASSERT usage when we added the first version of code.

C11 standard supports runtime violation handler registration.
We investigated the behavior of
(1) MS Visual Studio - http://msdn.microsoft.com/en-us/library/bb288454.aspx
(2) SafeCLib - http://sourceforge.net/projects/safeclib/
(3) Slibc - https://code.google.com/p/slibc/

The default behavior is:
(1) Call Debugger
(2) Print error
(3) Call abort()

As conclusion, we believe it is *caller's responsibility* to make sure the caller inputs right parameter, instead of let callee check and return error.

In order to catch such error as early as possible, we decide to use ASSERT, because it is something never happen. (We still use error handling followed by to handle the release build.)

This API is NOT design to handle untrusted input. As such, we believe it is expected ASSERT behavior.


We have other debate, such as if we need ASSERT 2 bytes alignment CHAR16 process, or if we need ASSERT address alignment for MMIO access.
Per our experience, it is much better to let caller guarantee that, instead of callee check that. And ASSERT is a good way to catch the issue as early as possible.



Thank you
Yao Jiewen

> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Vitaly
> Cheptsov via Groups.Io
> Sent: Monday, October 21, 2019 3:28 PM
> To: Yao, Jiewen <jiewen.yao@intel.com>; Gao, Liming <liming.gao@intel.com>
> Cc: devel@edk2.groups.io; Wang, Jian J <jian.j.wang@intel.com>; Kinney,
> Michael D <michael.d.kinney@intel.com>
> Subject: Re: [edk2-devel] [PATCH v1 1/1] MdePkg: Add PCD to disable safe string
> constraint assertions
> 
> Liming, Jiewen,
> 
> I am personally fine to resubmit the patch changing the defaults to TRUE, but
> does it actually make sense in any other environment but some special testing
> platform? I cannot imagine any production platform that would need it enabled,
> the only use case is to perform analysis on the trusted data usage or something
> similar, as I explained on BZ.
> 
> As for assertions, I would expect that all PCDs we introduce are meant to
> control unexpected ASSERT behaviour. I.e. where ASSERTs are potentially used
> to signalise about issues coming not only from trusted sources (usage contract
> violation) but also from untrusted sources (external data). Such assertions
> cannot be used in production environments, as they may break software, and
> thus we have to implement code to disable them.
> 
> Best regards,
> Vitaly
> 
> > 21 окт. 2019 г., в 7:28, Yao, Jiewen <jiewen.yao@intel.com> написал(а):
> >
> >
> > Hi Mike
> > I remember we have discussed it before.
> >
> > The general concern is that: how many additional PCD we need introduce, to
> control different ASSERT in different modules ?
> >
> > We may want to enable *some* assert in some modules, but disable *some
> other* assert.
> > E.g. the assert for linkedlist in base lib is another example...
> >
> > What is your thought?
> >
> > Thank you
> > Yao Jiewen
> >
> >> -----Original Message-----
> >> From: Gao, Liming <liming.gao@intel.com>
> >> Sent: Monday, October 21, 2019 11:17 AM
> >> To: devel@edk2.groups.io; vit9696@protonmail.com
> >> Cc: Yao, Jiewen <jiewen.yao@intel.com>; Wang, Jian J
> <jian.j.wang@intel.com>;
> >> Gao, Liming <liming.gao@intel.com>; Kinney, Michael D
> >> <michael.d.kinney@intel.com>
> >> Subject: RE: [edk2-devel] [PATCH v1 1/1] MdePkg: Add PCD to disable safe
> string
> >> constraint assertions
> >>
> >> Include more people.
> >>
> >> Basically, to keep the compatible behavior,
> PcdAssertOnSafeStringConstraints
> >> default value should be TRUE.
> >> The different platform can configure it.
> >>
> >> Thanks
> >> Liming
> >>> -----Original Message-----
> >>> From: devel@edk2.groups.io [mailto:devel@edk2.groups.io] On Behalf Of
> >>> Vitaly Cheptsov via Groups.Io
> >>> Sent: Sunday, October 20, 2019 9:06 PM
> >>> To: devel@edk2.groups.io
> >>> Subject: [edk2-devel] [PATCH v1 1/1] MdePkg: Add PCD to disable safe
> string
> >>> constraint assertions
> >>>
> >>> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2054
> >>>
> >>> Runtime data checks are not meant to cause debug assertions
> >>> unless explicitly needed by some debug code (thus the PCD)
> >>> as this breaks debug builds validating data with BaseLib.
> >>>
> >>> Signed-off-by: Vitaly Cheptsov <vit9696@protonmail.com>>
> >>> ---
> >>> MdePkg/MdePkg.dec                   |  6 ++++++
> >>> MdePkg/Library/BaseLib/BaseLib.inf  | 11 ++++++-----
> >>> MdePkg/Library/BaseLib/SafeString.c |  4 +++-
> >>> MdePkg/MdePkg.uni                   |  6 ++++++
> >>> 4 files changed, 21 insertions(+), 6 deletions(-)
> >>>
> >>> diff --git a/MdePkg/MdePkg.dec b/MdePkg/MdePkg.dec
> >>> index 3fd7d1634c..dda2cdf401 100644
> >>> --- a/MdePkg/MdePkg.dec
> >>> +++ b/MdePkg/MdePkg.dec
> >>> @@ -2221,6 +2221,12 @@ [PcdsFixedAtBuild,PcdsPatchableInModule]
> >>>  # @Prompt Memory Address of GuidedExtractHandler Table.
> >>>
> >>>
> gEfiMdePkgTokenSpaceGuid.PcdGuidedExtractHandlerTableAddress|0x10000
> >>> 00|UINT64|0x30001015
> >>>
> >>> +  ## Indicates if safe string constraint violation should assert.<BR><BR>
> >>> +  #   TRUE  - Safe string constraint violation causes assertion.<BR>
> >>> +  #   FALSE - Safe string constraint violation does not cause assertion.<BR>
> >>> +  # @Prompt Enable safe string constraint violation assertions.
> >>> +
> >>>
> gEfiMdePkgTokenSpaceGuid.PcdAssertOnSafeStringConstraints|FALSE|BOOL
> >>> EAN|0x0000002e
> >>> +
> >>> [PcdsFixedAtBuild, PcdsPatchableInModule, PcdsDynamic, PcdsDynamicEx]
> >>>  ## This value is used to set the base address of PCI express hierarchy.
> >>>  # @Prompt PCI Express Base Address.
> >>> diff --git a/MdePkg/Library/BaseLib/BaseLib.inf
> >>> b/MdePkg/Library/BaseLib/BaseLib.inf
> >>> index 3586beb0ab..bc98bc6134 100644
> >>> --- a/MdePkg/Library/BaseLib/BaseLib.inf
> >>> +++ b/MdePkg/Library/BaseLib/BaseLib.inf
> >>> @@ -390,11 +390,12 @@ [LibraryClasses]
> >>>  BaseMemoryLib
> >>>
> >>> [Pcd]
> >>> -  gEfiMdePkgTokenSpaceGuid.PcdMaximumLinkedListLength      ##
> >>> SOMETIMES_CONSUMES
> >>> -  gEfiMdePkgTokenSpaceGuid.PcdMaximumAsciiStringLength     ##
> >>> SOMETIMES_CONSUMES
> >>> -  gEfiMdePkgTokenSpaceGuid.PcdMaximumUnicodeStringLength   ##
> >>> SOMETIMES_CONSUMES
> >>> -  gEfiMdePkgTokenSpaceGuid.PcdControlFlowEnforcementPropertyMask
> >>> ## SOMETIMES_CONSUMES
> >>> -  gEfiMdePkgTokenSpaceGuid.PcdSpeculationBarrierType       ##
> >>> SOMETIMES_CONSUMES
> >>> +  gEfiMdePkgTokenSpaceGuid.PcdAssertOnSafeStringConstraints       ##
> >>> SOMETIMES_CONSUMES
> >>> +  gEfiMdePkgTokenSpaceGuid.PcdMaximumLinkedListLength             ##
> >>> SOMETIMES_CONSUMES
> >>> +  gEfiMdePkgTokenSpaceGuid.PcdMaximumAsciiStringLength            ##
> >>> SOMETIMES_CONSUMES
> >>> +  gEfiMdePkgTokenSpaceGuid.PcdMaximumUnicodeStringLength          ##
> >>> SOMETIMES_CONSUMES
> >>> +  gEfiMdePkgTokenSpaceGuid.PcdControlFlowEnforcementPropertyMask
> >>> ## SOMETIMES_CONSUMES
> >>> +  gEfiMdePkgTokenSpaceGuid.PcdSpeculationBarrierType              ##
> >>> SOMETIMES_CONSUMES
> >>>
> >>> [FeaturePcd]
> >>>  gEfiMdePkgTokenSpaceGuid.PcdVerifyNodeInList  ## CONSUMES
> >>> diff --git a/MdePkg/Library/BaseLib/SafeString.c
> >>> b/MdePkg/Library/BaseLib/SafeString.c
> >>> index 7dc03d2caa..56b5e34a8d 100644
> >>> --- a/MdePkg/Library/BaseLib/SafeString.c
> >>> +++ b/MdePkg/Library/BaseLib/SafeString.c
> >>> @@ -14,7 +14,9 @@
> >>>
> >>> #define SAFE_STRING_CONSTRAINT_CHECK(Expression, Status)  \
> >>>  do { \
> >>> -    ASSERT (Expression); \
> >>> +    if (PcdGetBool (PcdAssertOnSafeStringConstraints)) { \
> >>> +      ASSERT (Expression); \
> >>> +    } \
> >>>    if (!(Expression)) { \
> >>>      return Status; \
> >>>    } \
> >>> diff --git a/MdePkg/MdePkg.uni b/MdePkg/MdePkg.uni
> >>> index 5c1fa24065..425b66bb43 100644
> >>> --- a/MdePkg/MdePkg.uni
> >>> +++ b/MdePkg/MdePkg.uni
> >>> @@ -287,6 +287,12 @@
> >>>
> >>> #string
> >>> STR_gEfiMdePkgTokenSpaceGuid_PcdGuidedExtractHandlerTableAddress_H
> >>> ELP  #language en-US "This value is used to set the available memory
> address
> >>> to store Guided Extract Handlers. The required memory space is decided by
> >>> the value of PcdMaximumGuidedExtractHandler."
> >>>
> >>> +#string
> >>> STR_gEfiMdePkgTokenSpaceGuid_PcdAssertOnSafeStringConstraints_PROM
> >>> PT  #language en-US "Enable safe string constraint violation assertions"
> >>> +
> >>> +#string
> >>> STR_gEfiMdePkgTokenSpaceGuid_PcdAssertOnSafeStringConstraints_HELP
> >>> #language en-US "Indicates if safe string constraint violation should
> >>> assert.<BR><BR>\n"
> >>> +                                                                                   "TRUE  - Safe string
> constraint
> >>> violation causes assertion.<BR>\n"
> >>> +                                                                                   "FALSE - Safe string
> constraint
> >>> violation does not cause assertion.<BR>"
> >>> +
> >>> #string
> >>> STR_gEfiMdePkgTokenSpaceGuid_PcdPciExpressBaseAddress_PROMPT
> >>> #language en-US "PCI Express Base Address"
> >>>
> >>> #string STR_gEfiMdePkgTokenSpaceGuid_PcdPciExpressBaseAddress_HELP
> >>> #language en-US "This value is used to set the base address of PCI express
> >>> hierarchy."
> >>> --
> >>> 2.21.0 (Apple Git-122)
> >>>
> >>>
> >>> -=-=-=-=-=-=
> >>> Groups.io Links: You receive all messages sent to this group.
> >>>
> >>> View/Reply Online (#49255):
> https://edk2.groups.io/g/devel/message/49255
> >>> Mute This Topic: https://groups.io/mt/35943317/1759384
> >>> Group Owner: devel+owner@edk2.groups.io
> >>> Unsubscribe: https://edk2.groups.io/g/devel/unsub  [liming.gao@intel.com]
> >>> -=-=-=-=-=-=
> >
> 
> 
>