[PATCH 2/2] UefiCpuPkg/CpuDxe: Guarantee GDT is below 4GB


Ni, Ray
 

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3D3233

GDT needs to be allocated below 4GB in 64bit environment
because AP needs it for entering to protected mode.
CPU running in big real mode cannot access above 4GB GDT.

But CpuDxe driver contains below code:
gdt =3D AllocateRuntimePool (sizeof (GdtTemplate) + 8);
.....
gdtPtr.Base =3D (UINT32)(UINTN)(VOID*) gdt;

The AllocateRuntimePool() may allocate memory above 4GB.
Thus, we cannot use AllocateRuntimePool (), instead,
we should use AllocatePages() to make sure GDT is below 4GB space.

Signed-off-by: Ray Ni <ray.ni@...>
Cc: Eric Dong <eric.dong@...>
Cc: Laszlo Ersek <lersek@...>
Cc: Rahul Kumar <rahul1.kumar@...>
---
UefiCpuPkg/CpuDxe/CpuGdt.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/UefiCpuPkg/CpuDxe/CpuGdt.c b/UefiCpuPkg/CpuDxe/CpuGdt.c
index 322ce87142..98d5551702 100644
--- a/UefiCpuPkg/CpuDxe/CpuGdt.c
+++ b/UefiCpuPkg/CpuDxe/CpuGdt.c
@@ -124,15 +124,26 @@ InitGlobalDescriptorTable (
VOID=0D
)=0D
{=0D
+ EFI_STATUS Status;=0D
GDT_ENTRIES *Gdt;=0D
IA32_DESCRIPTOR Gdtr;=0D
+ EFI_PHYSICAL_ADDRESS Memory;=0D
=0D
//=0D
- // Allocate Runtime Data for the GDT=0D
- //=0D
- Gdt =3D AllocateRuntimePool (sizeof (gGdtTemplate) + 8);=0D
- ASSERT (Gdt !=3D NULL);=0D
- Gdt =3D ALIGN_POINTER (Gdt, 8);=0D
+ // Allocate Runtime Data below 4GB for the GDT=0D
+ // AP uses the same GDT when it's waken up from real mode so=0D
+ // the GDT needs to be below 4GB.=0D
+ //=0D
+ Memory =3D SIZE_4GB - 1;=0D
+ Status =3D gBS->AllocatePages (=0D
+ AllocateMaxAddress,=0D
+ EfiRuntimeServicesData,=0D
+ EFI_SIZE_TO_PAGES (sizeof (gGdtTemplate)),=0D
+ &Memory=0D
+ );=0D
+ ASSERT_EFI_ERROR (Status);=0D
+ ASSERT ((Memory !=3D 0) && (Memory < SIZE_4GB));=0D
+ Gdt =3D (GDT_ENTRIES *) (UINTN) Memory;=0D
=0D
//=0D
// Initialize all GDT entries=0D
--=20
2.27.0.windows.1


Dong, Eric
 

Reviewed-by: Eric Dong <eric.dong@...>

-----Original Message-----
From: Ni, Ray <ray.ni@...>
Sent: Tuesday, March 16, 2021 11:34 AM
To: devel@edk2.groups.io
Cc: Dong, Eric <eric.dong@...>; Laszlo Ersek <lersek@...>; Kumar, Rahul1 <rahul1.kumar@...>
Subject: [PATCH 2/2] UefiCpuPkg/CpuDxe: Guarantee GDT is below 4GB

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3233

GDT needs to be allocated below 4GB in 64bit environment
because AP needs it for entering to protected mode.
CPU running in big real mode cannot access above 4GB GDT.

But CpuDxe driver contains below code:
gdt = AllocateRuntimePool (sizeof (GdtTemplate) + 8);
.....
gdtPtr.Base = (UINT32)(UINTN)(VOID*) gdt;

The AllocateRuntimePool() may allocate memory above 4GB.
Thus, we cannot use AllocateRuntimePool (), instead,
we should use AllocatePages() to make sure GDT is below 4GB space.

Signed-off-by: Ray Ni <ray.ni@...>
Cc: Eric Dong <eric.dong@...>
Cc: Laszlo Ersek <lersek@...>
Cc: Rahul Kumar <rahul1.kumar@...>
---
UefiCpuPkg/CpuDxe/CpuGdt.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/UefiCpuPkg/CpuDxe/CpuGdt.c b/UefiCpuPkg/CpuDxe/CpuGdt.c
index 322ce87142..98d5551702 100644
--- a/UefiCpuPkg/CpuDxe/CpuGdt.c
+++ b/UefiCpuPkg/CpuDxe/CpuGdt.c
@@ -124,15 +124,26 @@ InitGlobalDescriptorTable (
VOID

)

{

+ EFI_STATUS Status;

GDT_ENTRIES *Gdt;

IA32_DESCRIPTOR Gdtr;

+ EFI_PHYSICAL_ADDRESS Memory;



//

- // Allocate Runtime Data for the GDT

- //

- Gdt = AllocateRuntimePool (sizeof (gGdtTemplate) + 8);

- ASSERT (Gdt != NULL);

- Gdt = ALIGN_POINTER (Gdt, 8);

+ // Allocate Runtime Data below 4GB for the GDT

+ // AP uses the same GDT when it's waken up from real mode so

+ // the GDT needs to be below 4GB.

+ //

+ Memory = SIZE_4GB - 1;

+ Status = gBS->AllocatePages (

+ AllocateMaxAddress,

+ EfiRuntimeServicesData,

+ EFI_SIZE_TO_PAGES (sizeof (gGdtTemplate)),

+ &Memory

+ );

+ ASSERT_EFI_ERROR (Status);

+ ASSERT ((Memory != 0) && (Memory < SIZE_4GB));

+ Gdt = (GDT_ENTRIES *) (UINTN) Memory;



//

// Initialize all GDT entries

--
2.27.0.windows.1


Laszlo Ersek
 

On 03/16/21 04:33, Ray Ni wrote:
REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3233

GDT needs to be allocated below 4GB in 64bit environment
because AP needs it for entering to protected mode.
CPU running in big real mode cannot access above 4GB GDT.

But CpuDxe driver contains below code:
gdt = AllocateRuntimePool (sizeof (GdtTemplate) + 8);
.....
gdtPtr.Base = (UINT32)(UINTN)(VOID*) gdt;

The AllocateRuntimePool() may allocate memory above 4GB.
Thus, we cannot use AllocateRuntimePool (), instead,
we should use AllocatePages() to make sure GDT is below 4GB space.

Signed-off-by: Ray Ni <ray.ni@...>
Cc: Eric Dong <eric.dong@...>
Cc: Laszlo Ersek <lersek@...>
Cc: Rahul Kumar <rahul1.kumar@...>
---
UefiCpuPkg/CpuDxe/CpuGdt.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/UefiCpuPkg/CpuDxe/CpuGdt.c b/UefiCpuPkg/CpuDxe/CpuGdt.c
index 322ce87142..98d5551702 100644
--- a/UefiCpuPkg/CpuDxe/CpuGdt.c
+++ b/UefiCpuPkg/CpuDxe/CpuGdt.c
@@ -124,15 +124,26 @@ InitGlobalDescriptorTable (
VOID
)
{
+ EFI_STATUS Status;
GDT_ENTRIES *Gdt;
IA32_DESCRIPTOR Gdtr;
+ EFI_PHYSICAL_ADDRESS Memory;

//
- // Allocate Runtime Data for the GDT
- //
- Gdt = AllocateRuntimePool (sizeof (gGdtTemplate) + 8);
- ASSERT (Gdt != NULL);
- Gdt = ALIGN_POINTER (Gdt, 8);
+ // Allocate Runtime Data below 4GB for the GDT
+ // AP uses the same GDT when it's waken up from real mode so
(1) s/waken/woken/

+ // the GDT needs to be below 4GB.
+ //
+ Memory = SIZE_4GB - 1;
+ Status = gBS->AllocatePages (
+ AllocateMaxAddress,
+ EfiRuntimeServicesData,
+ EFI_SIZE_TO_PAGES (sizeof (gGdtTemplate)),
+ &Memory
+ );
+ ASSERT_EFI_ERROR (Status);
+ ASSERT ((Memory != 0) && (Memory < SIZE_4GB));
(2) Can we drop the (Memory < SIZE_4GB) sub-condition? That should be
guaranteed by the UEFI spec.

+ Gdt = (GDT_ENTRIES *) (UINTN) Memory;

//
// Initialize all GDT entries
Anyway...

Reviewed-by: Laszlo Ersek <lersek@...>

Thanks
Laszlo