Re: [PATCH] UefiCpuPkg/CpuExceptionHandlerLib: always clear descriptor data in advance

["Wang, Jian J" <jian.j.wang@intel.com>]

Laszlo,

Thanks for the comments. I'll update the code.

Regards,
Jian


> -----Original Message-----
> From: Laszlo Ersek [mailto:lersek@redhat.com]
> Sent: Thursday, October 18, 2018 1:57 AM
> To: Wang, Jian J <jian.j.wang@intel.com>; edk2-devel@lists.01.org
> Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ruiyu <ruiyu.ni@intel.com>
> Subject: Re: [PATCH] UefiCpuPkg/CpuExceptionHandlerLib: always clear
> descriptor data in advance
> 
> Hi Jian,
> 
> 
> On 10/17/18 10:34, Jian J Wang wrote:
> > REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1237
> >
> > Sometimes the memory will be contaminated by random data left in last
> > boot (warm reset). The code should not assume the allocated memory is
> > always filled with zero. This patch add code to clear data structure
> > used for stack switch to prevent such problem from happening.
> >
> > Cc: Eric Dong <eric.dong@intel.com>
> > Cc: Laszlo Ersek <lersek@redhat.com>
> > Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Jian J Wang <jian.j.wang@intel.com>
> > ---
> >  UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c |
> 3 +++
> >  UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c  |
> 3 +++
> >  2 files changed, 6 insertions(+)
> >
> > diff --git
> a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c
> b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c
> > index 031d0d35fa..eebd27a25d 100644
> > ---
> a/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c
> > +++
> b/UefiCpuPkg/Library/CpuExceptionHandlerLib/Ia32/ArchExceptionHandler.c
> > @@ -214,6 +214,7 @@ ArchSetupExcpetionStack (
> >    //
> >    TssBase = (UINTN)Tss;
> >
> > +  TssDesc->Uint64          = 0;
> >    TssDesc->Bits.LimitLow   = sizeof(IA32_TASK_STATE_SEGMENT) - 1;
> >    TssDesc->Bits.BaseLow    = (UINT16)TssBase;
> >    TssDesc->Bits.BaseMid    = (UINT8)(TssBase >> 16);
> > @@ -238,6 +239,7 @@ ArchSetupExcpetionStack (
> >      //
> >      TssBase = (UINTN)Tss;
> >
> > +    TssDesc->Uint64         = 0;
> >      TssDesc->Bits.LimitLow  = sizeof(IA32_TASK_STATE_SEGMENT) - 1;
> >      TssDesc->Bits.BaseLow   = (UINT16)TssBase;
> >      TssDesc->Bits.BaseMid   = (UINT8)(TssBase >> 16);
> > @@ -255,6 +257,7 @@ ArchSetupExcpetionStack (
> >        continue;
> >      }
> >
> > +    SetMem (Tss, sizeof (IA32_TASK_STATE_SEGMENT), 0);
> >      Tss->EIP    = (UINT32)(TemplateMap.ExceptionStart
> >                             + Vector * TemplateMap.ExceptionStubHeaderSize);
> >      Tss->EFLAGS = 0x2;
> > diff --git
> a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
> b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
> > index 93ecf5ae5a..6745bc77c0 100644
> > ---
> a/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
> > +++
> b/UefiCpuPkg/Library/CpuExceptionHandlerLib/X64/ArchExceptionHandler.c
> > @@ -219,6 +219,8 @@ ArchSetupExcpetionStack (
> >    //
> >    TssBase = (UINTN)Tss;
> >
> > +  TssDesc->Uint128.Uint64  = 0;
> > +  TssDesc->Uint128.Uint64_1= 0;
> >    TssDesc->Bits.LimitLow   = sizeof(IA32_TASK_STATE_SEGMENT) - 1;
> >    TssDesc->Bits.BaseLow    = (UINT16)TssBase;
> >    TssDesc->Bits.BaseMidl   = (UINT8)(TssBase >> 16);
> > @@ -231,6 +233,7 @@ ArchSetupExcpetionStack (
> >    //
> >    // Fixup exception task descriptor and task-state segment
> >    //
> > +  SetMem (Tss, sizeof (IA32_TASK_STATE_SEGMENT), 0);
> >    StackTop = StackSwitchData->X64.KnownGoodStackTop -
> CPU_STACK_ALIGNMENT;
> >    StackTop = (UINTN)ALIGN_POINTER (StackTop, CPU_STACK_ALIGNMENT);
> >    IdtTable = StackSwitchData->X64.IdtTable;
> >
> 
> it can be checked whether this patch is complete (i.e. whether it covers
> all such places) and whether it is sound (i.e. what it does is correct).
> I can only offer to check the 2nd question. The patch seems correct, yes.
> 
> However, I would like to suggest two style improvements:
> 
> (1) Rather than SetMem (..., 0), I suggest ZeroMem().
> 
> (2) In general, I find
> 
>   ZeroMem (Tss, sizeof *Tss);
> 
> easier to read than
> 
>   ZeroMem (Tss, sizeof (IA32_TASK_STATE_SEGMENT));
> 
> 
> If you agree, feel free to update the code before pushing. (Do await
> feedback from Eric however.)
> 
> With or without the updates:
> 
> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
> 
> Thanks
> Laszlo