ArmVirtQemu: Allow EFI memory attributes protocol to be disabled

Shim's PE loader uses the EFI memory attributes protocol in a way that
results in an immediate crash when invoking the loaded image, unless the
base and size of its executable segment are both aligned to 4k.

If this is not the case, it will strip the memory allocation of its
executable permissions, but fail to add them back for the executable
region, resulting in non-executable code. Unfortunately, the PE loader
does not even bother invoking the protocol in this case (as it notices
the misalignment), making it very hard for system firmware to work
around this by attempting to infer the intent of the caller.

So let's introduce a QEMU command line option to indicate that the
protocol should not be exposed at all, and a PCD to set the default for
this option when it is omitted.

Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Link: https://gitlab.com/qemu-project/qemu/-/issues/1990
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

ArmVirtPkg/ArmVirtPkg.dec

@@ -68,3 +68,9 @@
   # Cloud Hypervisor has no other way to pass Rsdp address to the guest except use a PCD.
   #
   gArmVirtTokenSpaceGuid.PcdCloudHvAcpiRsdpBaseAddress|0x0|UINT64|0x00000005
+
+  ##
+  # Whether the EFI memory attributes protocol should be uninstalled before
+  # invoking the OS loader. This may be needed to work around problematic
+  # builds of shim that use the protocol incorrectly.
+  gArmVirtTokenSpaceGuid.PcdUninstallMemAttrProtocol|FALSE|BOOLEAN|0x00000006

ArmVirtPkg/Library/PlatformBootManagerLib/PlatformBm.c

@@ -16,6 +16,7 @@
 #include <Library/PcdLib.h>
 #include <Library/PlatformBmPrintScLib.h>
 #include <Library/QemuBootOrderLib.h>
+#include <Library/QemuFwCfgSimpleParserLib.h>
 #include <Library/TpmPlatformHierarchyLib.h>
 #include <Library/UefiBootManagerLib.h>
 #include <Protocol/DevicePath.h>
@@ -1111,6 +1112,49 @@ PlatformBootManagerBeforeConsole (
   FilterAndProcess (&gEfiPciIoProtocolGuid, IsVirtioPciSerial, SetupVirtioSerial);
 }
 
+/**
+  Uninstall the EFI memory attribute protocol if it exists.
+**/
+STATIC
+VOID
+UninstallEfiMemoryAttributesProtocol (
+  VOID
+  )
+{
+  EFI_STATUS  Status;
+  EFI_HANDLE  Handle;
+  UINTN       Size;
+  VOID        *MemoryAttributeProtocol;
+
+  Size   = sizeof (Handle);
+  Status = gBS->LocateHandle (
+                  ByProtocol,
+                  &gEfiMemoryAttributeProtocolGuid,
+                  NULL,
+                  &Size,
+                  &Handle
+                  );
+
+  if (EFI_ERROR (Status)) {
+    ASSERT (Status == EFI_NOT_FOUND);
+    return;
+  }
+
+  Status = gBS->HandleProtocol (
+                  Handle,
+                  &gEfiMemoryAttributeProtocolGuid,
+                  &MemoryAttributeProtocol
+                  );
+  ASSERT_EFI_ERROR (Status);
+
+  Status = gBS->UninstallProtocolInterface (
+                  Handle,
+                  &gEfiMemoryAttributeProtocolGuid,
+                  MemoryAttributeProtocol
+                  );
+  ASSERT_EFI_ERROR (Status);
+}
+
 /**
   Do the platform specific action after the console is ready
   Possible things that can be done in PlatformBootManagerAfterConsole:
@@ -1129,12 +1173,32 @@ PlatformBootManagerAfterConsole (
   )
 {
   RETURN_STATUS  Status;
+  BOOLEAN        Uninstall;
 
   //
   // Show the splash screen.
   //
   BootLogoEnableLogo ();
 
+  //
+  // Work around shim's terminally broken use of the EFI memory attributes
+  // protocol, by uninstalling it if requested on the QEMU command line.
+  //
+  // E.g.,
+  //       -fw_cfg opt/org.tianocore/UninstallMemAttrProtocol,string=y
+  //
+  Uninstall = FixedPcdGetBool (PcdUninstallMemAttrProtocol);
+  QemuFwCfgParseBool ("opt/org.tianocore/UninstallMemAttrProtocol", &Uninstall);
+  DEBUG ((
+    DEBUG_WARN,
+    "%a: %auninstalling EFI memory protocol\n",
+    __func__,
+    Uninstall ? "" : "not "
+    ));
+  if (Uninstall) {
+    UninstallEfiMemoryAttributesProtocol ();
+  }
+
   //
   // Process QEMU's -kernel command line option. The kernel booted this way
   // will receive ACPI tables: in PlatformBootManagerBeforeConsole(), we

ArmVirtPkg/Library/PlatformBootManagerLib/PlatformBootManagerLib.inf

@@ -46,6 +46,7 @@
   PcdLib
   PlatformBmPrintScLib
   QemuBootOrderLib
+  QemuFwCfgSimpleParserLib
   QemuLoadImageLib
   ReportStatusCodeLib
   TpmPlatformHierarchyLib
@@ -55,6 +56,7 @@
   UefiRuntimeServicesTableLib
 
 [FixedPcd]
+  gArmVirtTokenSpaceGuid.PcdUninstallMemAttrProtocol
   gEfiMdePkgTokenSpaceGuid.PcdUartDefaultBaudRate
   gEfiMdePkgTokenSpaceGuid.PcdUartDefaultDataBits
   gEfiMdePkgTokenSpaceGuid.PcdUartDefaultParity
@@ -73,5 +75,6 @@
 [Protocols]
   gEfiFirmwareVolume2ProtocolGuid
   gEfiGraphicsOutputProtocolGuid
+  gEfiMemoryAttributeProtocolGuid
   gEfiPciRootBridgeIoProtocolGuid
   gVirtioDeviceProtocolGuid