Re: [edk2-devel] [PATCH v2 2/4] StandaloneMmPkg/Hob: Integer Overflow in CreateHob()

["Sami Mujawar" <sami.mujawar@arm.com>]

Hi Gua,

Thank you for this patch.
Please see my response inline marked [SAMI].

Regards,

Sami Mujawar

On 11/01/2024, 09:15, "gua.guo@intel.com <mailto:gua.guo@intel.com>" <gua.guo@intel.com <mailto:gua.guo@intel.com>> wrote:


From: Gua Guo <gua.guo@intel.com <mailto:gua.guo@intel.com>>


REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4166 <https://bugzilla.tianocore.org/show_bug.cgi?id=4166>


Fix integer overflow in various CreateHob instances.
Fixes: CVE-2022-36765


The CreateHob() function aligns the requested size to 8
performing the following operation:
```
HobLength = (UINT16)((HobLength + 0x7) & (~0x7));
```


No checks are performed to ensure this value doesn't
overflow, and could lead to CreateHob() returning a smaller
HOB than requested, which could lead to OOB HOB accesses.


Reported-by: Marc Beatove <mbeatove@google.com <mailto:mbeatove@google.com>>
Reviewed-by: Ard Biesheuvel <ardb+tianocore@kernel.org <mailto:ardb+tianocore@kernel.org>>
Cc: Sami Mujawar <sami.mujawar@arm.com <mailto:sami.mujawar@arm.com>>
Cc: Ray Ni <ray.ni@intel.com <mailto:ray.ni@intel.com>>
Cc: John Mathew <john.mathews@intel.com <mailto:john.mathews@intel.com>>
Authored-by: Gerd Hoffmann <kraxel@redhat.com <mailto:kraxel@redhat.com>>
Signed-off-by: Gua Guo <gua.guo@intel.com <mailto:gua.guo@intel.com>>
---
.../StandaloneMmCoreHobLib/Arm/StandaloneMmCoreHobLib.c | 7 +++++++
1 file changed, 7 insertions(+)


diff --git a/StandaloneMmPkg/Library/StandaloneMmCoreHobLib/Arm/StandaloneMmCoreHobLib.c b/StandaloneMmPkg/Library/StandaloneMmCoreHobLib/Arm/StandaloneMmCoreHobLib.c
index 1550e1babc..bb8426dc0a 100644
--- a/StandaloneMmPkg/Library/StandaloneMmCoreHobLib/Arm/StandaloneMmCoreHobLib.c
+++ b/StandaloneMmPkg/Library/StandaloneMmCoreHobLib/Arm/StandaloneMmCoreHobLib.c
@@ -34,6 +34,13 @@ CreateHob (




HandOffHob = GetHobList ();






+ //


+ // Check Length to avoid data overflow.


+ //


+ if (HobLength > MAX_UINT16 - 0x7) {


+ return NULL;
[SAMI] Although this fix is correct, I think it shifts the problem somewhere else. 
If the above condition occurs, a NULL is returned. A quick scan reveals that the calling functions do not check the returned value before use.
e.g. https://github.com/tianocore/edk2/blob/master/StandaloneMmPkg/Library/StandaloneMmCoreHobLib/Arm/StandaloneMmCoreHobLib.c#L167-L170
There are multiple such places where the calling functions do not check the pointer returned by CreateHob(). 
I believe a similar situation can happen for the other patches in this series.
[/SAMI]

+ }


+


HobLength = (UINT16)((HobLength + 0x7) & (~0x7));






FreeMemory = HandOffHob->EfiFreeMemoryTop - HandOffHob->EfiFreeMemoryBottom;


-- 
2.39.2.windows.1







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