[PATCH] UefiCpuPkg: Fix CPU stack guard support by aligning GDT buffer


Vitaly Cheptsov
 

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)


Vitaly Cheptsov
 

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.



Vitaly Cheptsov
 

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;


Leif Lindholm
 

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)








Vitaly Cheptsov
 

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)








Michael D Kinney
 

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)








Vitaly Cheptsov
 

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)








Michael D Kinney
 

Hi Vitaly,

So IA32 CLANGPDB is likely putting the UINTT8 array global mNewGdt
on a 4-byte boundary, when it would have to be on an 8-byte boundary
to meet the GDT alignment requirements.

I would expect the X64 CLANGPDB build to use an 8-byte boundary.

Another option to align to 8-byte boundary is to make the array an
array of UINT64 values. To be more correct, we could use an array
of IA32_SEGMENT_DESCRIPTOR structures that is a union with a
UINT64 to guarantee 8-byte alignment.

typedef union {
struct {
UINT32 LimitLow:16;
UINT32 BaseLow:16;
UINT32 BaseMid:8;
UINT32 Type:4;
UINT32 S:1;
UINT32 DPL:2;
UINT32 P:1;
UINT32 LimitHigh:4;
UINT32 AVL:1;
UINT32 L:1;
UINT32 DB:1;
UINT32 G:1;
UINT32 BaseHigh:8;
} Bits;
UINT64 Uint64;
} IA32_SEGMENT_DESCRIPTOR;

IA32_SEGMENT_DESCRIPTOR mNewGdt[(CPU_TSS_GDT_SIZE / sizeof (IA32_SEGMENT_DESCRIPTOR)) + 1];

Add 1 in case CPU_TSS_GDT_SIZE is not 8-byte aligned in size.


For come of the logic, you would still need to introduce a UINT8 * local variable
to compute the start of each component in this array.

I think in other places, the GDT is allocated using AllocatePool()
which guarantees an 8-byte alignment.

Are you suggesting that the ALIGNAS macro would map to the compiler
specific alignment directives? We have not had to introduce that yet
and would like to figure out how to address this one issues without
adding those directives.

Mike

-----Original Message-----
From: Vitaly Cheptsov <cheptsov@ispras.ru>
Sent: Friday, November 5, 2021 1:36 PM
To: Kinney, Michael D <michael.d.kinney@intel.com>
Cc: Leif Lindholm <leif@nuviainc.com>; devel@edk2.groups.io; Yao, Jiewen <jiewen.yao@intel.com>; Dong, Eric
<eric.dong@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

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)








Vitaly Cheptsov
 

Hi Mike,

I am aware of this possibility, but it feels unnecessary ugly in my opinion. Marvin has already sent a patch alignment-related patches not so long ago[1], updating this with V3 and using as a ground feels like a much better choice.

Best wishes,
Vitaly

[1] https://edk2.groups.io/g/devel/message/78887?p=%2C%2C%2C100%2C0%2C0%2C0%3A%3Arecentpostdate%2Fsticky%2C%2CALIGNOF%2C100%2C2%2C0%2C84754061

On 6 Nov 2021, at 00:39, Kinney, Michael D <michael.d.kinney@intel.com> wrote:

Hi Vitaly,

So IA32 CLANGPDB is likely putting the UINTT8 array global mNewGdt
on a 4-byte boundary, when it would have to be on an 8-byte boundary
to meet the GDT alignment requirements.

I would expect the X64 CLANGPDB build to use an 8-byte boundary.

Another option to align to 8-byte boundary is to make the array an
array of UINT64 values. To be more correct, we could use an array
of IA32_SEGMENT_DESCRIPTOR structures that is a union with a
UINT64 to guarantee 8-byte alignment.

typedef union {
struct {
UINT32 LimitLow:16;
UINT32 BaseLow:16;
UINT32 BaseMid:8;
UINT32 Type:4;
UINT32 S:1;
UINT32 DPL:2;
UINT32 P:1;
UINT32 LimitHigh:4;
UINT32 AVL:1;
UINT32 L:1;
UINT32 DB:1;
UINT32 G:1;
UINT32 BaseHigh:8;
} Bits;
UINT64 Uint64;
} IA32_SEGMENT_DESCRIPTOR;

IA32_SEGMENT_DESCRIPTOR mNewGdt[(CPU_TSS_GDT_SIZE / sizeof (IA32_SEGMENT_DESCRIPTOR)) + 1];

Add 1 in case CPU_TSS_GDT_SIZE is not 8-byte aligned in size.


For come of the logic, you would still need to introduce a UINT8 * local variable
to compute the start of each component in this array.

I think in other places, the GDT is allocated using AllocatePool()
which guarantees an 8-byte alignment.

Are you suggesting that the ALIGNAS macro would map to the compiler
specific alignment directives? We have not had to introduce that yet
and would like to figure out how to address this one issues without
adding those directives.

Mike

-----Original Message-----
From: Vitaly Cheptsov <cheptsov@ispras.ru>
Sent: Friday, November 5, 2021 1:36 PM
To: Kinney, Michael D <michael.d.kinney@intel.com>
Cc: Leif Lindholm <leif@nuviainc.com>; devel@edk2.groups.io; Yao, Jiewen <jiewen.yao@intel.com>; Dong, Eric
<eric.dong@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

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)








Leif Lindholm
 



On Fri, Nov 5, 2021 at 7:37 PM Vitaly Cheptsov <cheptsov@...> wrote:
>
> Hi Leif,
>
> I assume you mean the commit description, because the commit message is in the topic.

A topic is not a commit message. The commit message is what comes after 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.

But I'm happy with this one.

Best Regards,

Leif

> Best wishes,
> Vitaly
>
> > On 5 Nov 2021, at 22:28, Leif Lindholm <leif@...> 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@...>
> >>
> >> Cc: Eric Dong <eric.dong@...>
> >>
> >> Cc: Michael Kinney <michael.d.kinney@...>
> >>
> >> Cc: Jian J Wang <jian.j.wang@...>
> >>
> >> Cc: Jeff Fan <vanjeff_919@...>
> >>
> >> Cc: Mikhail Krichanov <krichanov@...>
> >>
> >> Cc: Marvin Häuser <mhaeuser@...>
> >>
> >> Signed-off-by: Vitaly Cheptsov <cheptsov@...>
> >>
> >> ---
> >>
> >> .../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)
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>