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


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@...> 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@...>
Sent: Friday, November 5, 2021 12:28 PM
To: devel@edk2.groups.io; cheptsov@...
Cc: Yao, Jiewen <jiewen.yao@...>; Dong, Eric <eric.dong@...>; Kinney, Michael D <michael.d.kinney@...>;
Wang, Jian J <jian.j.wang@...>; Jeff Fan <vanjeff_919@...>; Mikhail Krichanov <krichanov@...>; Marvin
Häuser <mhaeuser@...>
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@...>

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)







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