Commits on Nov 21, 2020

1. MdeModulePkg/Core/Dxe: assert SectionInstance invariant in FindChildN… …

   …ode()
   
   FindChildNode() has two callers: GetSection(), and FindChildNode() itself.
   
   - At the GetSection() call site, a positive (i.e., nonzero)
     SectionInstance is passed. This is because GetSection() takes a
     zero-based (UINTN) SectionInstance, and then passes
     Instance=(SectionInstance+1) to FindChildNode().
   
   - For reaching the recursive FindChildNode() call site, a section type
     mismatch, or a section instance mismatch, is necessary. This means,
     respectively, that SectionInstance will either not have been decreased,
     or not to zero anyway, at the recursive FindChildNode() call site.
   
   Add two ASSERT()s to FindChildNode(), for expressing the (SectionSize>0)
   invariant.
   
   In turn, the invariant provides the explanation why, after the recursive
   call, a zero SectionInstance implies success. Capture it in a comment.
   
   Cc: Dandan Bi <dandan.bi@intel.com>
   Cc: Hao A Wu <hao.a.wu@intel.com>
   Cc: Jian J Wang <jian.j.wang@intel.com>
   Cc: Liming Gao <gaoliming@byosoft.com.cn>
   Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
   Signed-off-by: Laszlo Ersek <lersek@redhat.com>
   Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
   Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
   Message-Id: <20201119105340.16225-2-lersek@redhat.com>

   

   lersek committed Nov 21, 2020
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2. MdeModulePkg/Core/Dxe: limit FwVol encapsulation section recursion …

   The DXE Core sets up a protocol notify function in its entry point, for
   instances of the Firmware Volume Block2 Protocol:
   
     DxeMain()           [DxeMain/DxeMain.c]
       FwVolDriverInit() [FwVol/FwVol.c]
   
   Assume that a 3rd party UEFI driver or application installs an FVB
   instance, with crafted contents. The notification function runs:
   
     NotifyFwVolBlock() [FwVol/FwVol.c]
   
   installing an instance of the Firmware Volume 2 Protocol on the handle.
   
   (Alternatively, assume that a 3rd party application calls
   gDS->ProcessFirmwareVolume(), which may also produce a Firmware Volume 2
   Protocol instance.)
   
   The EFI_FIRMWARE_VOLUME2_PROTOCOL.ReadSection() member performs "a
   depth-first, left-to-right search algorithm through all sections found in
   the specified file" (quoting the PI spec), as follows:
   
     FvReadFileSection()   [FwVol/FwVolRead.c]
       GetSection()        [SectionExtraction/CoreSectionExtraction.c]
         FindChildNode()   [SectionExtraction/CoreSectionExtraction.c]
           FindChildNode() // recursive call
   
   FindChildNode() is called recursively for encapsulation sections.
   
   Currently this recursion is not limited. Introduce a new PCD
   (fixed-at-build, or patchable-in-module), and make FindChildNode() track
   the section nesting depth against that PCD.
   
   Cc: Dandan Bi <dandan.bi@intel.com>
   Cc: Hao A Wu <hao.a.wu@intel.com>
   Cc: Jian J Wang <jian.j.wang@intel.com>
   Cc: Liming Gao <gaoliming@byosoft.com.cn>
   Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
   Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1743
   Signed-off-by: Laszlo Ersek <lersek@redhat.com>
   Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>
   Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
   Message-Id: <20201119105340.16225-3-lersek@redhat.com>

   

   lersek committed Nov 21, 2020
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