x86/efi: Wire up CONFIG_EFI_MIXED

Add the Kconfig option and bump the kernel header version so that boot
loaders can check whether the handover code is available if they want.

The xloadflags field in the bzImage header is also updated to reflect
that the kernel supports both entry points by setting both of
XLF_EFI_HANDOVER_32 and XLF_EFI_HANDOVER_64 when CONFIG_EFI_MIXED=y.
XLF_CAN_BE_LOADED_ABOVE_4G is disabled so that the kernel text is
guaranteed to be addressable with 32-bits.

Note that no boot loaders should be using the bits set in xloadflags to
decide which entry point to jump to. The entire scheme is based on the
concept that 32-bit bootloaders always jump to ->handover_offset and
64-bit loaders always jump to ->handover_offset + 512. We set both bits
merely to inform the boot loader that it's safe to use the native
handover offset even if the machine type in the PE/COFF header claims
otherwise.

Signed-off-by: Matt Fleming <matt.fleming@intel.com>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0af5250d914fd7b52d01873571dd6facb7bba8d4..8453fe1342eaf137bcf2c707bc93ac4717ee27db 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1585,6 +1585,20 @@ config EFI_STUB
 
          See Documentation/efi-stub.txt for more information.
 
+config EFI_MIXED
+       bool "EFI mixed-mode support"
+       depends on EFI_STUB && X86_64
+       ---help---
+          Enabling this feature allows a 64-bit kernel to be booted
+          on a 32-bit firmware, provided that your CPU supports 64-bit
+          mode.
+
+          Note that it is not possible to boot a mixed-mode enabled
+          kernel via the EFI boot stub - a bootloader that supports
+          the EFI handover protocol must be used.
+
+          If unsure, say N.
+
 config SECCOMP
        def_bool y
        prompt "Enable seccomp to safely compute untrusted bytecode"

diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index d69d96653325818ff8f37ca18360b96c7b3b6703..256388260c8869c0a018dc39a7e2a78520838481 100644 (file)
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -283,7 +283,7 @@ _start:
        # Part 2 of the header, from the old setup.S
 
                .ascii  "HdrS"          # header signature
-               .word   0x020c          # header version number (>= 0x0105)
+               .word   0x020d          # header version number (>= 0x0105)
                                        # or else old loadlin-1.5 will fail)
                .globl realmode_swtch
 realmode_swtch:        .word   0, 0            # default_switch, SETUPSEG
@@ -375,7 +375,8 @@ xloadflags:
 # define XLF0 0
 #endif
 
-#if defined(CONFIG_RELOCATABLE) && defined(CONFIG_X86_64)
+#if defined(CONFIG_RELOCATABLE) && defined(CONFIG_X86_64) && \
+       !defined(CONFIG_EFI_MIXED)
    /* kernel/boot_param/ramdisk could be loaded above 4g */
 # define XLF1 XLF_CAN_BE_LOADED_ABOVE_4G
 #else
@@ -383,10 +384,14 @@ xloadflags:
 #endif
 
 #ifdef CONFIG_EFI_STUB
-# ifdef CONFIG_X86_64
-#  define XLF23 XLF_EFI_HANDOVER_64            /* 64-bit EFI handover ok */
+# ifdef CONFIG_EFI_MIXED
+#  define XLF23 (XLF_EFI_HANDOVER_32|XLF_EFI_HANDOVER_64)
 # else
-#  define XLF23 XLF_EFI_HANDOVER_32            /* 32-bit EFI handover ok */
+#  ifdef CONFIG_X86_64
+#   define XLF23 XLF_EFI_HANDOVER_64           /* 64-bit EFI handover ok */
+#  else
+#   define XLF23 XLF_EFI_HANDOVER_32           /* 32-bit EFI handover ok */
+#  endif
 # endif
 #else
 # define XLF23 0

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 85935e6f69f3c530ad1fc2cacd17f19d9b5db104..a3837254e3202137ed97d5ecc8d9fa0b0591dc24 100644 (file)
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -152,6 +152,17 @@ static inline bool efi_is_native(void)
        return IS_ENABLED(CONFIG_X86_64) == efi_enabled(EFI_64BIT);
 }
 
+static inline bool efi_runtime_supported(void)
+{
+       if (efi_is_native())
+               return true;
+
+       if (IS_ENABLED(CONFIG_EFI_MIXED) && !efi_enabled(EFI_OLD_MEMMAP))
+               return true;
+
+       return false;
+}
+
 extern struct console early_efi_console;
 extern void parse_efi_setup(u64 phys_addr, u32 data_len);
 

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 06853e6703541f8349106e17330f86621fa984db..ff9b3a62a05cfd75b9891ba73e0d7d52a84828d5 100644 (file)
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -1243,7 +1243,7 @@ void __init setup_arch(char **cmdline_p)
         * mismatched firmware/kernel archtectures since there is no
         * support for runtime services.
         */
-       if (efi_enabled(EFI_BOOT) && !efi_is_native()) {
+       if (efi_enabled(EFI_BOOT) && !efi_runtime_supported()) {
                pr_info("efi: Setup done, disabling due to 32/64-bit mismatch\n");
                efi_unmap_memmap();
        }

diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index 39f5b7bba695b67fc17ce099dc4dc5b8f25aa037..395decedfa2bf4f9167c6012a8a1157e8e4d8253 100644 (file)
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -802,7 +802,7 @@ void __init efi_init(void)
         * that doesn't match the kernel 32/64-bit mode.
         */
 
-       if (!efi_is_native())
+       if (!efi_runtime_supported())
                pr_info("No EFI runtime due to 32/64-bit mismatch with kernel\n");
        else {
                if (disable_runtime || efi_runtime_init())