From 42d273d28b65b72e580c37f674c620cc50c1677d Mon Sep 17 00:00:00 2001
From: Gerd Hoffmann <kraxel@redhat.com>
Date: Wed, 10 Apr 2024 17:25:03 +0200
Subject: [PATCH] OvmfPkg/X86QemuLoadImageLib: support booting via shim

Try load shim first.  In case that succeeded update the command line to
list 'kernel' first so shim will fetch the kernel from the kernel loader
file system.

This allows to use direct kernel boot with distro kernels and secure
boot enabled.  Usually distro kernels can only be verified by distro
shim using the distro keys compiled into the shim binary.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 .../X86QemuLoadImageLib/X86QemuLoadImageLib.c | 51 ++++++++++++++++++-
 1 file changed, 49 insertions(+), 2 deletions(-)

diff --git a/OvmfPkg/Library/X86QemuLoadImageLib/X86QemuLoadImageLib.c b/OvmfPkg/Library/X86QemuLoadImageLib/X86QemuLoadImageLib.c
index a7ab43ca7415..bf6b461fbb26 100644
--- a/OvmfPkg/Library/X86QemuLoadImageLib/X86QemuLoadImageLib.c
+++ b/OvmfPkg/Library/X86QemuLoadImageLib/X86QemuLoadImageLib.c
@@ -57,6 +57,25 @@ STATIC CONST KERNEL_VENMEDIA_FILE_DEVPATH  mKernelDevicePath = {
   }
 };
 
+STATIC CONST KERNEL_VENMEDIA_FILE_DEVPATH  mShimDevicePath = {
+  {
+    {
+      MEDIA_DEVICE_PATH, MEDIA_VENDOR_DP,
+      { sizeof (VENDOR_DEVICE_PATH)       }
+    },
+    QEMU_KERNEL_LOADER_FS_MEDIA_GUID
+  },  {
+    {
+      MEDIA_DEVICE_PATH, MEDIA_FILEPATH_DP,
+      { sizeof (KERNEL_FILE_DEVPATH)      }
+    },
+    L"shim",
+  },  {
+    END_DEVICE_PATH_TYPE, END_ENTIRE_DEVICE_PATH_SUBTYPE,
+    { sizeof (EFI_DEVICE_PATH_PROTOCOL) }
+  }
+};
+
 STATIC
 VOID
 FreeLegacyImage (
@@ -339,6 +358,7 @@ QemuLoadKernelImage (
   UINTN                      CommandLineSize;
   CHAR8                      *CommandLine;
   UINTN                      InitrdSize;
+  BOOLEAN                    Shim;
 
   //
   // Redundant assignment to work around GCC48/GCC49 limitations.
@@ -351,11 +371,30 @@ QemuLoadKernelImage (
   Status = gBS->LoadImage (
                   FALSE,                    // BootPolicy: exact match required
                   gImageHandle,             // ParentImageHandle
-                  (EFI_DEVICE_PATH_PROTOCOL *)&mKernelDevicePath,
+                  (EFI_DEVICE_PATH_PROTOCOL *)&mShimDevicePath,
                   NULL,                     // SourceBuffer
                   0,                        // SourceSize
                   &KernelImageHandle
                   );
+  if (Status == EFI_SUCCESS) {
+    Shim = TRUE;
+    DEBUG ((DEBUG_INFO, "%a: booting via shim\n", __func__));
+  } else {
+    Shim = FALSE;
+    if (Status == EFI_SECURITY_VIOLATION) {
+      gBS->UnloadImage (KernelImageHandle);
+    }
+
+    Status = gBS->LoadImage (
+                    FALSE,                  // BootPolicy: exact match required
+                    gImageHandle,           // ParentImageHandle
+                    (EFI_DEVICE_PATH_PROTOCOL *)&mKernelDevicePath,
+                    NULL,                   // SourceBuffer
+                    0,                      // SourceSize
+                    &KernelImageHandle
+                    );
+  }
+
   switch (Status) {
     case EFI_SUCCESS:
       break;
@@ -465,6 +504,13 @@ QemuLoadKernelImage (
     KernelLoadedImage->LoadOptionsSize += sizeof (L" initrd=initrd") - 2;
   }
 
+  if (Shim) {
+    //
+    // Prefix 'kernel ' in UTF-16.
+    //
+    KernelLoadedImage->LoadOptionsSize += sizeof (L"kernel ") - 2;
+  }
+
   if (KernelLoadedImage->LoadOptionsSize == 0) {
     KernelLoadedImage->LoadOptions = NULL;
   } else {
@@ -485,7 +531,8 @@ QemuLoadKernelImage (
     UnicodeSPrintAsciiFormat (
       KernelLoadedImage->LoadOptions,
       KernelLoadedImage->LoadOptionsSize,
-      "%a%a",
+      "%a%a%a",
+      (Shim == FALSE)        ?  "" : "kernel ",
       (CommandLineSize == 0) ?  "" : CommandLine,
       (InitrdSize == 0)      ?  "" : " initrd=initrd"
       );