Re: Stack issue after warm UEFI reset and MMU enabling on an Armv8 platform

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 19 September 2018 at 15:55, Vladimir Olovyannikov <
vladimir.olovyannikov@broadcom.com> wrote:

> Hi All,
>
>
>
> I need UEFI experts help on the problem with Armv8 board on warm UEFI
> reset.
>
> Cold reset works fine.
>
>
>
> Here is how I set up a warm reset:
>
>
>
> STATIC
>
> EFI_STATUS
>
> ShutdownUefiBootServices (
>
>   VOID
>
>   )
>
> {
>
>   EFI_STATUS              Status;
>
>   UINTN                   MemoryMapSize;
>
>   EFI_MEMORY_DESCRIPTOR   *MemoryMap;
>
>   UINTN                   MapKey;
>
>   UINTN                   DescriptorSize;
>
>   UINT32                  DescriptorVersion;
>
>   UINTN                   Pages;
>
>
>
>   MemoryMap = NULL;
>
>   MemoryMapSize = 0;
>
>   Pages = 0;
>
>
>
>   do {
>
>     Status = gBS->GetMemoryMap (
>
>                     &MemoryMapSize,
>
>                     MemoryMap,
>
>                     &MapKey,
>
>                     &DescriptorSize,
>
>                     &DescriptorVersion
>
>                     );
>
>     if (Status == EFI_BUFFER_TOO_SMALL) {
>
>
>
>       Pages = EFI_SIZE_TO_PAGES (MemoryMapSize) + 1;
>
>       MemoryMap = AllocatePages (Pages);
>
>
>
>       //
>
>       // Get System MemoryMap
>
>       //
>
>       Status = gBS->GetMemoryMap (
>
>                       &MemoryMapSize,
>
>                       MemoryMap,
>
>                       &MapKey,
>
>                       &DescriptorSize,
>
>                       &DescriptorVersion
>
>                       );
>
>     }
>
>
>
>     // Don't do anything between the GetMemoryMap() and ExitBootServices()
>
>     if (!EFI_ERROR(Status)) {
>
>       Status = gBS->ExitBootServices (gImageHandle, MapKey);
>
>       if (EFI_ERROR(Status)) {
>
>         FreePages (MemoryMap, Pages);
>
>         MemoryMap = NULL;
>
>         MemoryMapSize = 0;
>
>       }
>
>     }
>
>   } while (EFI_ERROR(Status));
>
>
>
>   return Status;
>
> }
>
>
>
> Then perform
>
> ArmCleanDataCache ();
>
> ArmInvalidateDataCache ();
>
> ArmDisableInstructionCache ();
>
> ArmInvalidateInstructionCache ();
>

These don't do anything useful on ARM. You can only reliably perform cache
maintenance by virtual address.

ArmDisableMmu ();
>
>
>

... so after this call returns, all bets are off with regards to whether
what is popped from the stack is actually what we pushed when we entered
the function.

> Then jump to start of FV:
>
>
>
> typedef
>
> VOID
>
> (EFIAPI *START_FV)(
>
>   VOID
>
> );
>
> StartOfFv = (START_FV)(UINTN)PcdGet64(PcdFvBaseAddress);
>
> StartOfFv ();
>
>
>
> Now this is what happens on warm reset:
>
> reset -c warm
>
> 1. Until ArmEnableMmu() gets called, everything works as expected.
>
>     Here is the stack right before ArmEnableMmu() is called:
>
>      ArmConfigureMmu+0x4f8
>
>      InitMmu+0x24
>
>      MemoryPeim+0x440
>
>      PrePiMain+0x114
>
>      PrimaryMain+0x68
>
>      CEntryPoint+0xC4
>
>      EL2:0x00000000800008BC
>
>      -----  End of stack info -----
>
>
>
> 2. Here is the stack as soon as Mmu is enabled with ArmEnableMmu() :
>
>     ArmConfigureMmu+0x4fc <-- This one is correct, at line 745 in
> ArmConfigureMmu() in ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> (return EFI_SUCCESS)
>
>    _ModuleEntryPoint+0x24 <-- Wrong. This points directly to
> ASSERT(FALSE); and to CpuDeadLoop() in DxeCoreEntryPoint.c, lines 59-60.
>
>    El2:0x000000008E5E8300 <-- Absolutely bogus
>
>     --- End of stack info ---
>
>
>
> So, as soon as ArmEnableMmu() exits, execution jumps directly to
> CpuDeadLoop() in DxeCoreEntryPoint of _ModuleEntryPoint().
>
>
>
> Would be grateful for any advice.
>
>
>
> Thank you,
>
> Vladimir
>
>
>