[PATCH edk2-platforms v2 1/1] Platform/ARM/ArmShellCmdRunAxf: switch to by-VA cache maintenance

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

Currently, the 'runaxf' shell command that exists only on ARM's own
development platforms deals with the caches in an unsafe manner, as
it relies on set/way maintenance to ensure that the ELF image it has
put into memory, as well as the running image itself is visible in
memory after the MMU and caches are disabled.

So let's switch to by-VA maintenance for the currently running image,
as well as the ELF image, and use a helper in assembly to ensure that
we are not relying on the stack between the disabling of the MMU and
the invocation of the ELF image.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
v2:
- call ArmDisableMmu() directly from the pivot code, instead of via an
  indirect branch
- move ArmDisableDataCache() call into the pivot code as well
- perform I-cache invalidation on the loaded ELF image, but leave the
  I-cache enabled

 Platform/ARM/Library/ArmShellCmdRunAxf/AArch64/Pivot.S       | 41 +++++++++
 Platform/ARM/Library/ArmShellCmdRunAxf/Arm/Pivot.S           | 41 +++++++++
 Platform/ARM/Library/ArmShellCmdRunAxf/ArmShellCmdRunAxf.inf |  8 ++
 Platform/ARM/Library/ArmShellCmdRunAxf/RunAxf.c              | 89 +++++++++-----------
 4 files changed, 131 insertions(+), 48 deletions(-)

diff --git a/Platform/ARM/Library/ArmShellCmdRunAxf/AArch64/Pivot.S b/Platform/ARM/Library/ArmShellCmdRunAxf/AArch64/Pivot.S
new file mode 100644
index 000000000000..1ab4b15f127b
--- /dev/null
+++ b/Platform/ARM/Library/ArmShellCmdRunAxf/AArch64/Pivot.S
@@ -0,0 +1,41 @@
+//
+//  Copyright (c) 2020, ARM Limited. All rights reserved.
+//
+//  SPDX-License-Identifier: BSD-2-Clause-Patent
+//
+
+#include <AsmMacroIoLibV8.h>
+
+// VOID
+// RunAxfPivot (
+//   IN  ELF_ENTRYPOINT  ElfEntry
+//   IN  UINTN           Arg0,
+//   IN  UINTN           Arg1,
+//   IN  UINTN           Arg2,
+//   IN  UINTN           Arg3
+//   );
+ASM_FUNC(RunAxfPivot)
+  // Preserve ElfEntry() and its arguments
+  // Since we will not be returning from this function, we can clobber
+  // callee preserved register instead.
+  mov   x19, x0
+  mov   x20, x1
+  mov   x21, x2
+  mov   x22, x3
+  mov   x23, x4
+
+  bl    ArmDisableDataCache
+  bl    ArmDisableMmu
+
+  // Load ElfEntry()'s arguments into x0...x3
+  mov   x0, x20
+  mov   x1, x21
+  mov   x2, x22
+  mov   x3, x23
+
+  // Call ElfEntry()
+  blr   x19
+
+0:wfi
+  wfe
+  b     0b
diff --git a/Platform/ARM/Library/ArmShellCmdRunAxf/Arm/Pivot.S b/Platform/ARM/Library/ArmShellCmdRunAxf/Arm/Pivot.S
new file mode 100644
index 000000000000..50efcfacdfe6
--- /dev/null
+++ b/Platform/ARM/Library/ArmShellCmdRunAxf/Arm/Pivot.S
@@ -0,0 +1,41 @@
+//
+//  Copyright (c) 2020, ARM Limited. All rights reserved.
+//
+//  SPDX-License-Identifier: BSD-2-Clause-Patent
+//
+
+#include <AsmMacroIoLibV8.h>
+
+// VOID
+// RunAxfPivot (
+//   IN  ELF_ENTRYPOINT  ElfEntry
+//   IN  UINTN           Arg0,
+//   IN  UINTN           Arg1,
+//   IN  UINTN           Arg2,
+//   IN  UINTN           Arg3
+//   );
+ASM_FUNC(RunAxfPivot)
+  // Preserve ElfEntry() and its arguments without using the stack.
+  // Since we will not be returning from this function, we can clobber
+  // callee preserved register instead.
+  mov   r4, r0
+  mov   r5, r1
+  mov   r6, r2
+  mov   r7, r3
+  pop   {r8}
+
+  bl    ArmDisableDataCache
+  bl    ArmDisableMmu
+
+  // Load ElfEntry()'s arguments into x0...x3
+  mov   r0, r5
+  mov   r1, r6
+  mov   r2, r7
+  mov   r3, r8
+
+  // Call ElfEntry()
+  blx   r4
+
+0:wfi
+  wfe
+  b     0b
diff --git a/Platform/ARM/Library/ArmShellCmdRunAxf/ArmShellCmdRunAxf.inf b/Platform/ARM/Library/ArmShellCmdRunAxf/ArmShellCmdRunAxf.inf
index 74c6a0e84fdf..7c27a765bd5c 100644
--- a/Platform/ARM/Library/ArmShellCmdRunAxf/ArmShellCmdRunAxf.inf
+++ b/Platform/ARM/Library/ArmShellCmdRunAxf/ArmShellCmdRunAxf.inf
@@ -27,6 +27,12 @@ [Sources.common]
   elf64.h
   elf_common.h
 
+[Sources.AARCH64]
+  AArch64/Pivot.S
+
+[Sources.ARM]
+  Arm/Pivot.S
+
 [Packages]
   ArmPkg/ArmPkg.dec
   MdeModulePkg/MdeModulePkg.dec
@@ -37,11 +43,13 @@ [Packages]
 [LibraryClasses]
   ArmLib
   BaseLib
+  CacheMaintenanceLib
   DebugLib
   HiiLib
   ShellLib
 
 [Protocols]
+  gEfiLoadedImageProtocolGuid
   gEfiShellDynamicCommandProtocolGuid
 
 [Guids]
diff --git a/Platform/ARM/Library/ArmShellCmdRunAxf/RunAxf.c b/Platform/ARM/Library/ArmShellCmdRunAxf/RunAxf.c
index 153aed2ab6bd..dbad50ae866a 100644
--- a/Platform/ARM/Library/ArmShellCmdRunAxf/RunAxf.c
+++ b/Platform/ARM/Library/ArmShellCmdRunAxf/RunAxf.c
@@ -10,6 +10,7 @@
 
 #include <Guid/GlobalVariable.h>
 
+#include <Library/CacheMaintenanceLib.h>
 #include <Library/PrintLib.h>
 #include <Library/HandleParsingLib.h>
 #include <Library/DevicePathLib.h>
@@ -20,6 +21,8 @@
 
 #include <Library/ArmLib.h>
 
+#include <Protocol/LoadedImage.h>
+
 #include "ArmShellCmdRunAxf.h"
 #include "ElfLoader.h"
 #include "BootMonFsLoader.h"
@@ -85,37 +88,21 @@ ShutdownUefiBootServices (
   return Status;
 }
 
-
-STATIC
-EFI_STATUS
-PreparePlatformHardware (
-  VOID
-  )
-{
-  //Note: Interrupts will be disabled by the GIC driver when ExitBootServices() will be called.
-
-  // Clean before Disable else the Stack gets corrupted with old data.
-  ArmCleanDataCache ();
-  ArmDisableDataCache ();
-  // Invalidate all the entries that might have snuck in.
-  ArmInvalidateDataCache ();
-
-  // Disable and invalidate the instruction cache
-  ArmDisableInstructionCache ();
-  ArmInvalidateInstructionCache ();
-
-  // Turn off MMU
-  ArmDisableMmu();
-
-  return EFI_SUCCESS;
-}
-
 // Process arguments to pass to AXF?
 STATIC CONST SHELL_PARAM_ITEM ParamList[] = {
   {NULL, TypeMax}
 };
 
 
+VOID
+RunAxfPivot (
+  IN  ELF_ENTRYPOINT  ElfEntry,
+  IN  UINTN           Arg0,
+  IN  UINTN           Arg1,
+  IN  UINTN           Arg2,
+  IN  UINTN           Arg3
+  );
+
 /**
   This is the shell command handler function pointer callback type. This
   function handles the command when it is invoked in the shell.
@@ -139,23 +126,23 @@ ShellDynCmdRunAxfHandler (
   IN EFI_SHELL_PROTOCOL                    *Shell
   )
 {
-  LIST_ENTRY        *ParamPackage;
-  EFI_STATUS         Status;
-  SHELL_STATUS       ShellStatus;
-  SHELL_FILE_HANDLE  FileHandle;
-  ELF_ENTRYPOINT     StartElf;
-  CONST CHAR16      *FileName;
-  EFI_FILE_INFO     *Info;
-  UINTN              FileSize;
-  VOID              *FileData;
-  VOID              *Entrypoint;
-  LIST_ENTRY         LoadList;
-  LIST_ENTRY        *Node;
-  LIST_ENTRY        *NextNode;
-  RUNAXF_LOAD_LIST  *LoadNode;
-  CHAR16            *TmpFileName;
-  CHAR16            *TmpChar16;
-
+  LIST_ENTRY                  *ParamPackage;
+  EFI_STATUS                  Status;
+  SHELL_STATUS                ShellStatus;
+  SHELL_FILE_HANDLE           FileHandle;
+  ELF_ENTRYPOINT              StartElf;
+  CONST CHAR16                *FileName;
+  EFI_FILE_INFO               *Info;
+  UINTN                       FileSize;
+  VOID                        *FileData;
+  VOID                        *Entrypoint;
+  LIST_ENTRY                  LoadList;
+  LIST_ENTRY                  *Node;
+  LIST_ENTRY                  *NextNode;
+  RUNAXF_LOAD_LIST            *LoadNode;
+  CHAR16                      *TmpFileName;
+  CHAR16                      *TmpChar16;
+  EFI_LOADED_IMAGE_PROTOCOL   *LoadedImage;
 
   ShellStatus = SHELL_SUCCESS;
   FileHandle = NULL;
@@ -291,6 +278,9 @@ ShellDynCmdRunAxfHandler (
     }
   }
 
+  WriteBackDataCacheRange (FileData, FileSize);
+  InvalidateInstructionCacheRange (FileData, FileSize);
+
   // Program load list created.
   // Shutdown UEFI, copy and jump to code.
   if (!IsListEmpty (&LoadList) && !EFI_ERROR (Status)) {
@@ -315,14 +305,17 @@ ShellDynCmdRunAxfHandler (
         Node = GetNextNode (&LoadList, Node);
       }
 
-      //
-      // Switch off interrupts, caches, mmu, etc
-      //
-      Status = PreparePlatformHardware ();
+      Status = gBS->HandleProtocol (gImageHandle, &gEfiLoadedImageProtocolGuid,
+                      (VOID **)&LoadedImage);
       ASSERT_EFI_ERROR (Status);
 
-      StartElf = (ELF_ENTRYPOINT)Entrypoint;
-      StartElf (0,0,0,0);
+      //
+      // Ensure that the currently running image is clean to the PoC so we can
+      // safely keep executing it with the MMU and caches off
+      //
+      WriteBackDataCacheRange (LoadedImage->ImageBase, LoadedImage->ImageSize);
+
+      RunAxfPivot (StartElf, 0, 0, 0, 0);
 
       // We should never get here.. But if we do, spin..
       ASSERT (FALSE);
-- 
2.17.1