[PATCH v4 4/4] efi: Do not use command line if secure boot is enabled.

[Trammell Hudson <hudson@xxxxxxxx>]

If secure boot is enabled, the Xen command line arguments are ignored.
If a unified Xen image is used, then the bundled configuration, dom0
kernel, and initrd are prefered over the ones listed in the config file.

Unlike the shim based verification, the PE signature on a unified image
covers the all of the Xen+config+kernel+initrd modules linked into the
unified image. This also ensures that properly configured platforms
will measure the entire runtime into the TPM for unsealing secrets or
remote attestation.

Signed-off-by: Trammell Hudson <hudson@xxxxxxxx>
---
 xen/common/efi/boot.c | 44 ++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 41 insertions(+), 3 deletions(-)

diff --git a/xen/common/efi/boot.c b/xen/common/efi/boot.c
index 4b1fbc9643..e65c1f1a09 100644
--- a/xen/common/efi/boot.c
+++ b/xen/common/efi/boot.c
@@ -949,6 +949,39 @@ static void __init setup_efi_pci(void)
     efi_bs->FreePool(handles);
 }
 
+/*
+ * Logic should remain sync'ed with linux/arch/x86/xen/efi.c
+ * Secure Boot is enabled iff 'SecureBoot' is set and the system is
+ * not in Setup Mode.
+ */
+static bool __init efi_secure_boot(void)
+{
+    static const __initconst EFI_GUID global_guid = EFI_GLOBAL_VARIABLE;
+    uint8_t secboot, setupmode;
+    UINTN secboot_size = sizeof(secboot);
+    UINTN setupmode_size = sizeof(setupmode);
+    EFI_STATUS rc;
+
+    rc = efi_rs->GetVariable(L"SecureBoot", (EFI_GUID *)&global_guid,
+                             NULL, &secboot_size, &secboot);
+    if ( rc != EFI_SUCCESS )
+        return false;
+
+    rc = efi_rs->GetVariable(L"SetupMode", (EFI_GUID *)&global_guid,
+                             NULL, &setupmode_size, &setupmode);
+    if ( rc != EFI_SUCCESS )
+        return false;
+
+    if ( secboot > 1)
+    {
+        PrintStr(L"Invalid SecureBoot variable=0x");
+        DisplayUint(secboot, 2);
+        PrintStr(newline);
+    }
+
+    return secboot == 1 && setupmode == 0;
+}
+
 static void __init efi_variables(void)
 {
     EFI_STATUS status;
@@ -1125,8 +1158,8 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE 
*SystemTable)
     static EFI_GUID __initdata shim_lock_guid = SHIM_LOCK_PROTOCOL_GUID;
     EFI_LOADED_IMAGE *loaded_image;
     EFI_STATUS status;
-    unsigned int i, argc;
-    CHAR16 **argv, *file_name, *cfg_file_name = NULL, *options = NULL;
+    unsigned int i, argc = 0;
+    CHAR16 **argv = NULL, *file_name, *cfg_file_name = NULL, *options = NULL;
     UINTN gop_mode = ~0;
     EFI_SHIM_LOCK_PROTOCOL *shim_lock;
     EFI_GRAPHICS_OUTPUT_PROTOCOL *gop = NULL;
@@ -1134,6 +1167,7 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE 
*SystemTable)
     bool base_video = false;
     char *option_str;
     bool use_cfg_file;
+    bool secure = false;
 
     __set_bit(EFI_BOOT, &efi_flags);
     __set_bit(EFI_LOADER, &efi_flags);
@@ -1152,8 +1186,10 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE 
*SystemTable)
         PrintErrMesg(L"No Loaded Image Protocol", status);
 
     efi_arch_load_addr_check(loaded_image);
+    secure = efi_secure_boot();
 
-    if ( use_cfg_file )
+    /* If UEFI Secure Boot is enabled, do not parse the command line */
+    if ( use_cfg_file && !secure )
     {
         UINTN offset = 0;
 
@@ -1211,6 +1247,8 @@ efi_start(EFI_HANDLE ImageHandle, EFI_SYSTEM_TABLE 
*SystemTable)
 
     PrintStr(L"Xen " __stringify(XEN_VERSION) "." __stringify(XEN_SUBVERSION)
              XEN_EXTRAVERSION " (c/s " XEN_CHANGESET ") EFI loader\r\n");
+    if ( secure )
+        PrintStr(L"UEFI Secure Boot enabled\r\n");
 
     efi_arch_relocate_image(0);
 
-- 
2.25.1