Re: [PATCH 2/2] UefiCpuPkg/PiSmmCpuDxeSmm: Fix ASSERT for success.

["Marvin Häuser" <Marvin.Haeuser@outlook.com>]

Hey Eric,

I discovered it by accident, no tool was involved.

Regards,
Marvin

> -----Original Message-----
> From: Dong, Eric <eric.dong@intel.com>
> Sent: Tuesday, October 30, 2018 3:30 AM
> To: Marvin Häuser <Marvin.Haeuser@outlook.com>; edk2-
> devel@lists.01.org
> Cc: lersek@redhat.com
> Subject: RE: [PATCH 2/2] UefiCpuPkg/PiSmmCpuDxeSmm: Fix ASSERT for
> success.
> 
> Hi Marvin,
> 
> Thanks for your contribution. I have reviewed them and pushed to trunk.
> SHA numbers are:
> SHA-1: 4222e8e7e421e9c8d2c2f319a3860dd3332d6255
> SHA-1: 37fba7c2762e114a280e3b361b53ded034aac7e3
> 
> One more question which just curious by me, how you find this issue? by tool
> or code review?
> 
> Thanks,
> Eric
> 
> > -----Original Message-----
> > From: Marvin Häuser [mailto:Marvin.Haeuser@outlook.com]
> > Sent: Sunday, October 28, 2018 4:51 PM
> > To: edk2-devel@lists.01.org
> > Cc: Dong, Eric <eric.dong@intel.com>; lersek@redhat.com
> > Subject: [PATCH 2/2] UefiCpuPkg/PiSmmCpuDxeSmm: Fix ASSERT for
> > success.
> >
> > Index is initialized to MAX_UINT16 as default failure value, which is
> > what the ASSERT is supposed to test for.  The ASSERT condition however
> > can never return FALSE for INT16 != int, as due to Integer
> > Promotion[1], Index is converted to int, which can never result in -1.
> >
> > Furthermore, Index is used as a for loop index variable inbetween its
> > initialization and the ASSERT, so the value is unconditionally overwritten
> too.
> >
> > Fix the ASSERT check to compare Index to its upper boundary, which it
> > will be equal to if the loop was not broken out of on success.
> >
> > [1] ISO/IEC 9899:2011, 6.5.9.4
> >
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Marvin Haeuser <Marvin.Haeuser@outlook.com>
> > ---
> >  UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c
> > b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c
> > index b7c3ad31e82c..89b3f2b7257f 100644
> > --- a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c
> > +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c
> > @@ -110,7 +110,6 @@ GetProtectedModeCS (
> >    UINTN                    GdtEntryCount;
> >    UINT16                   Index;
> >
> > -  Index = (UINT16) -1;
> >    AsmReadGdtr (&GdtrDesc);
> >    GdtEntryCount = (GdtrDesc.Limit + 1) / sizeof
> > (IA32_SEGMENT_DESCRIPTOR);
> >    GdtEntry = (IA32_SEGMENT_DESCRIPTOR *) GdtrDesc.Base; @@ -122,7
> > +121,7 @@ GetProtectedModeCS (
> >      }
> >      GdtEntry++;
> >    }
> > -  ASSERT (Index != -1);
> > +  ASSERT (Index != GdtEntryCount);
> >    return Index * 8;
> >  }
> >
> > --
> > 2.19.1.windows.1