[edk2-devel] [PATCH 2/2] UefiCpuPkg/CpuDxe: Guarantee GDT is below 4GB
Laszlo Ersek
lersek at redhat.com
Tue Mar 16 16:35:17 UTC 2021
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 at intel.com>
> Cc: Eric Dong <eric.dong at intel.com>
> Cc: Laszlo Ersek <lersek at redhat.com>
> Cc: Rahul Kumar <rahul1.kumar at intel.com>
> ---
> 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 at redhat.com>
Thanks
Laszlo
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