Re: [edk2-devel] [PATCH] UefiCpuPkg: Fix CPU stack guard support by aligning GDT buffer

["Vitaly Cheptsov" <cheptsov@ispras.ru>]

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Hello,

It has been over a month since the patch was sent. What is the state of the issue?

Best regards,
Vitaly

> On 20 Sep 2021, at 19:15, vit9696 via [] <vit9696=protonmail.com@[]> wrote:
> 
> Just to make it clear, this is an immediate solution that is good enough to fix the bug. However, a more proper solution would be to introduce the _Alignas concept to EDK II. I would suggest the following macro in Base.h:
> 
> /**
>   Enforce custom alignment for a variable definition.
>   Similar to C11 alignas macro from stdalign.h, except it must be functional to support MSVC.
> 
>   @param  Alignment  Numeric alignment to require.
> **/
> #ifdef _MSC_EXTENSIONS
>   #define ALIGNAS(Alignment) __declspec(align(Alignment))
> #else
>   #define ALIGNAS(Alignment) _Alignas(Alignment)
> #endif
> 
> If there is no disagreement on this, I can imagine submitting an update after this patch is merged.
> 
> 
>> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3639
>> 
>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>> Cc: Eric Dong <eric.dong@intel.com>
>> Cc: Michael Kinney <michael.d.kinney@intel.com>
>> Cc: Jian J Wang <jian.j.wang@intel.com>
>> Cc: Jeff Fan <vanjeff_919@hotmail.com>
>> Cc: Mikhail Krichanov <krichanov@ispras.ru>
>> Cc: Marvin Häuser <mhaeuser@posteo.de>
>> Signed-off-by: Vitaly Cheptsov <cheptsov@ispras.ru>
>> ---
>>  .../Library/CpuExceptionHandlerLib/DxeException.c    | 12 +++++++-----
>>  1 file changed, 7 insertions(+), 5 deletions(-)
>> 
>> diff --git a/UefiCpuPkg/Library/CpuExceptionHandlerLib/DxeException.c b/UefiCpuPkg/Library/CpuExceptionHandlerLib/DxeException.c
>> index fd59f09ecd..12874811e1 100644
>> --- a/UefiCpuPkg/Library/CpuExceptionHandlerLib/DxeException.c
>> +++ b/UefiCpuPkg/Library/CpuExceptionHandlerLib/DxeException.c
>> @@ -22,7 +22,7 @@ EXCEPTION_HANDLER_DATA      mExceptionHandlerData;
>> 
>>  UINT8                       mNewStack[CPU_STACK_SWITCH_EXCEPTION_NUMBER *
>>                                        CPU_KNOWN_GOOD_STACK_SIZE];
>> -UINT8                       mNewGdt[CPU_TSS_GDT_SIZE];
>> +UINT8                       mNewGdt[CPU_TSS_GDT_SIZE + IA32_GDT_ALIGNMENT];
>> 
>>  /**
>>    Common exception handler.
>> @@ -238,6 +238,7 @@ InitializeCpuExceptionHandlersEx (
>>    CPU_EXCEPTION_INIT_DATA           EssData;
>>    IA32_DESCRIPTOR                   Idtr;
>>    IA32_DESCRIPTOR                   Gdtr;
>> +  UINT8                             *Gdt;
>> 
>>    //
>>    // To avoid repeat initialization of default handlers, the caller should pass
>> @@ -259,6 +260,7 @@ InitializeCpuExceptionHandlersEx (
>>      if (PcdGetBool (PcdCpuStackGuard)) {
>>        if (InitData == NULL) {
>>          SetMem (mNewGdt, sizeof (mNewGdt), 0);
>> +        Gdt = ALIGN_POINTER (mNewGdt, IA32_GDT_ALIGNMENT);
>> 
>>          AsmReadIdtr (&Idtr);
>>          AsmReadGdtr (&Gdtr);
>> @@ -270,11 +272,11 @@ InitializeCpuExceptionHandlersEx (
>>          EssData.X64.StackSwitchExceptionNumber = CPU_STACK_SWITCH_EXCEPTION_NUMBER;
>>          EssData.X64.IdtTable = (VOID *)Idtr.Base;
>>          EssData.X64.IdtTableSize = Idtr.Limit + 1;
>> -        EssData.X64.GdtTable = mNewGdt;
>> -        EssData.X64.GdtTableSize = sizeof (mNewGdt);
>> -        EssData.X64.ExceptionTssDesc = mNewGdt + Gdtr.Limit + 1;
>> +        EssData.X64.GdtTable = Gdt;
>> +        EssData.X64.GdtTableSize = CPU_TSS_GDT_SIZE;
>> +        EssData.X64.ExceptionTssDesc = Gdt + Gdtr.Limit + 1;
>>          EssData.X64.ExceptionTssDescSize = CPU_TSS_DESC_SIZE;
>> -        EssData.X64.ExceptionTss = mNewGdt + Gdtr.Limit + 1 + CPU_TSS_DESC_SIZE;
>> +        EssData.X64.ExceptionTss = Gdt + Gdtr.Limit + 1 + CPU_TSS_DESC_SIZE;
>>          EssData.X64.ExceptionTssSize = CPU_TSS_SIZE;
>> 
>>          InitData = &EssData;
> 


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