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

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

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Hi Mike,

The command is:
build -a IA32 -p OvmfPkg/OvmfPkgIa32.dsc -t CLANGPDB -b NOOPT -D DEBUG_ON_SERIAL_PORT

But I obviously needed to add
gEfiMdeModulePkgTokenSpaceGuid.PcdCpuStackGuard|TRUE
to OvmfPkgIa32.dsc.

The compiler is clang 12.0.1, because clang 13 is badly broken[1]. It would then crash like this:

HandOffToDxeCore() Stack Base: 0x7FE24000, Stack Size: 0x20000

ASSERT_EFI_ERROR (Status = Invalid Parameter)
ASSERT [DxeCore] DxeMain.c(256): !EFI_ERROR (Status)

As for aligning the array, I can submit a V2 which introduces the ALIGNAS macro. I also like this solution a lot more.

Best wishes,
Vitaly

[1] https://bugzilla.tianocore.org/buglist.cgi?quicksearch=clang%2013&list_id=24276


> On 5 Nov 2021, at 22:42, Kinney, Michael D <michael.d.kinney@intel.com> wrote:
> 
> Hi Vitaly,
> 
> Can you please provide some details on the compiler/build command that did not align the array
> correctly.
> 
> I agree that the GDT must have the correct alignment.
> 
> I do not like the idea of unused bytes at the beginning of the array. I would prefer to see
> an array that is aligned correctly by declaration.
> 
> 
> Mike
> 
>> -----Original Message-----
>> From: Leif Lindholm <leif@nuviainc.com>
>> Sent: Friday, November 5, 2021 12:28 PM
>> To: devel@edk2.groups.io; cheptsov@ispras.ru
>> Cc: Yao, Jiewen <jiewen.yao@intel.com>; Dong, Eric <eric.dong@intel.com>; Kinney, Michael D <michael.d.kinney@intel.com>;
>> Wang, Jian J <jian.j.wang@intel.com>; Jeff Fan <vanjeff_919@hotmail.com>; Mikhail Krichanov <krichanov@ispras.ru>; Marvin
>> Häuser <mhaeuser@posteo.de>
>> Subject: Re: [edk2-devel] [PATCH] UefiCpuPkg: Fix CPU stack guard support by aligning GDT buffer
>> 
>> UefiCpuPkg maintainers - please respond.
>> 
>> Meanwhile, Vitaly, could you please provide a commit message?
>> The BZ link is needed, but it's not a substitute.
>> 
>> /
>>    Leif
>> 
>> On Mon, Sep 20, 2021 at 17:13:47 +0300, Vitaly Cheptsov wrote:
>>> 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;
>>> 
>>> --
>>> 
>>> 2.30.1 (Apple Git-130)
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 


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