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

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

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Hi Leif,

I assume you mean the commit description, because the commit message is in the topic. I believe something like that would do:

CpuExceptionHandlerLib supplies misaligned GDT to the outer world
(e.g. ArchSetupExceptionStack) when PcdCpuStackGuard is enabled.
This happens because it uses an array of UINT8 for the mNewGdt
variable, which alignment is 1 byte versus required 8 bytes. As a result
ArchSetupExceptionStack always returns EFI_INVALID_PARAMETER in OVMF Ia32
with XCODE5 and CLANGPDB at least.

Fix this by allocating extra space in mNewGdt and then aligning the pointer
upwards.

Best wishes,
Vitaly

> On 5 Nov 2021, at 22:28, Leif Lindholm <leif@nuviainc.com> wrote:
> 
> 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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