[PATCH 4/4] x86: Call Shim Verify in the multiboot2 path

[Ross Lagerwall <ross.lagerwall@citrix.com>]

Now that the multiboot2 binary can be verified by Shim, ensure that the
dom0 kernel is verified when using the multiboot2 path. If the Shim
protocol is not available and the SecureBoot variable is not set to 0
(or the state cannot be determined), abort the boot.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
---
 xen/arch/x86/boot/head.S    |  4 ++-
 xen/arch/x86/efi/efi-boot.h | 65 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S
index 84dc8b76b61d..7b6e5d3882ad 100644
--- a/xen/arch/x86/boot/head.S
+++ b/xen/arch/x86/boot/head.S
@@ -385,10 +385,12 @@ __efi64_mb2_start:
         /* Keep the stack aligned. Do not pop a single item off it. */
         mov     (%rsp),%rdi
 
+        mov     %rbx, %rcx
+
         /*
          * efi_multiboot2() is called according to System V AMD64 ABI:
          *   - IN:  %rdi - EFI ImageHandle, %rsi - EFI SystemTable,
-         *          %rdx - MB2 cmdline
+         *          %rdx - MB2 cmdline, %rcx - Multiboot information.
          */
         call    efi_multiboot2
 
diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
index 8ea64e31cdc2..a9569e150e08 100644
--- a/xen/arch/x86/efi/efi-boot.h
+++ b/xen/arch/x86/efi/efi-boot.h
@@ -3,6 +3,7 @@
  * is intended to be included by common/efi/boot.c _only_, and
  * therefore can define arch specific global variables.
  */
+#include <xen/multiboot2.h>
 #include <xen/vga.h>
 #include <asm/e820.h>
 #include <asm/edd.h>
@@ -808,9 +809,69 @@ static const char *__init get_option(const char *cmd, const char *opt)
     return o;
 }
 
+#define ALIGN_UP(arg, align) \
+                (((arg) + (align) - 1) & ~((typeof(arg))(align) - 1))
+
+static void __init efi_verify_dom0(uint64_t mbi_in)
+{
+    uint64_t ptr;
+    const multiboot2_tag_t *tag;
+    EFI_SHIM_LOCK_PROTOCOL *shim_lock;
+    EFI_STATUS status;
+    const multiboot2_tag_module_t *kernel = NULL;
+    const multiboot2_fixed_t *mbi_fix = _p(mbi_in);
+    static EFI_GUID __initdata shim_lock_guid = SHIM_LOCK_PROTOCOL_GUID;
+    static EFI_GUID __initdata global_variable_guid = EFI_GLOBAL_VARIABLE;
+
+    ptr = ALIGN_UP(mbi_in + sizeof(*mbi_fix), MULTIBOOT2_TAG_ALIGN);
+
+    for ( tag = _p(ptr); (uint64_t)tag - mbi_in < mbi_fix->total_size;
+          tag = _p(ALIGN_UP((uint64_t)tag + tag->size, MULTIBOOT2_TAG_ALIGN)) )
+    {
+        if ( tag->type == MULTIBOOT2_TAG_TYPE_MODULE )
+        {
+            kernel = (const multiboot2_tag_module_t *)tag;
+            break;
+        }
+        else if ( tag->type == MULTIBOOT2_TAG_TYPE_END )
+            break;
+    }
+
+    if ( !kernel )
+        return;
+
+    if ( (status = efi_bs->LocateProtocol(&shim_lock_guid, NULL,
+                                          (void **)&shim_lock)) != EFI_SUCCESS )
+    {
+        UINT32 attr;
+        UINT8 data;
+        UINTN size = sizeof(data);
+
+        status = efi_rs->GetVariable((CHAR16 *)L"SecureBoot", &global_variable_guid,
+                                     &attr, &size, &data);
+        if ( status == EFI_NOT_FOUND )
+            return;
+
+        if ( EFI_ERROR(status) )
+            PrintErrMesg(L"Could not get SecureBoot variable", status);
+
+        if ( attr != (EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS) )
+            PrintErrMesg(L"Unexpected SecureBoot attributes", attr);
+
+        if ( size == 1 && data == 0 )
+            return;
+
+        blexit(L"Could not locate shim but Secure Boot is enabled");
+    }
+
+    if ( (status = shim_lock->Verify(_p(kernel->mod_start),
+                                     kernel->mod_end - kernel->mod_start)) != EFI_SUCCESS )
+        PrintErrMesg(L"Dom0 kernel image could not be verified", status);
+}
+
 void asmlinkage __init efi_multiboot2(EFI_HANDLE ImageHandle,
                                       EFI_SYSTEM_TABLE *SystemTable,
-                                      const char *cmdline)
+                                      const char *cmdline, uint64_t mbi_in)
 {
     EFI_GRAPHICS_OUTPUT_PROTOCOL *gop;
     EFI_HANDLE gop_handle;
@@ -902,6 +963,8 @@ void asmlinkage __init efi_multiboot2(EFI_HANDLE ImageHandle,
 
     efi_relocate_esrt(SystemTable);
 
+    efi_verify_dom0(mbi_in);
+
     efi_exit_boot(ImageHandle, SystemTable);
 }
 
-- 
2.43.0