x86/efi: Firmware agnostic handover entry points

The EFI handover code only works if the "bitness" of the firmware and
the kernel match, i.e. 64-bit firmware and 64-bit kernel - it is not
possible to mix the two. This goes against the tradition that a 32-bit
kernel can be loaded on a 64-bit BIOS platform without having to do
anything special in the boot loader. Linux distributions, for one thing,
regularly run only 32-bit kernels on their live media.

Despite having only one 'handover_offset' field in the kernel header,
EFI boot loaders use two separate entry points to enter the kernel based
on the architecture the boot loader was compiled for,

    (1) 32-bit loader: handover_offset
    (2) 64-bit loader: handover_offset + 512

Since we already have two entry points, we can leverage them to infer
the bitness of the firmware we're running on, without requiring any boot
loader modifications, by making (1) and (2) valid entry points for both
CONFIG_X86_32 and CONFIG_X86_64 kernels.

To be clear, a 32-bit boot loader will always use (1) and a 64-bit boot
loader will always use (2). It's just that, if a single kernel image
supports (1) and (2) that image can be used with both 32-bit and 64-bit
boot loaders, and hence both 32-bit and 64-bit EFI.

(1) and (2) must be 512 bytes apart at all times, but that is already
part of the boot ABI and we could never change that delta without
breaking existing boot loaders anyhow.

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

diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
index 878df7e88cd4d9c4293d9540432fdd3d7c78fc6e..abb9eba61b500192cd816dd9283fe8c8fb70b858 100644 (file)
--- a/arch/x86/boot/Makefile
+++ b/arch/x86/boot/Makefile
@@ -80,7 +80,7 @@ targets += voffset.h
 $(obj)/voffset.h: vmlinux FORCE
        $(call if_changed,voffset)
 
-sed-zoffset := -e 's/^\([0-9a-fA-F]*\) . \(startup_32\|startup_64\|efi_pe_entry\|efi_stub_entry\|input_data\|_end\|z_.*\)$$/\#define ZO_\2 0x\1/p'
+sed-zoffset := -e 's/^\([0-9a-fA-F]*\) . \(startup_32\|startup_64\|efi32_stub_entry\|efi64_stub_entry\|efi_pe_entry\|input_data\|_end\|z_.*\)$$/\#define ZO_\2 0x\1/p'
 
 quiet_cmd_zoffset = ZOFFSET $@
       cmd_zoffset = $(NM) $< | sed -n $(sed-zoffset) > $@

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index ab1f3a2f1e1eea02d12f9e7142e4f1f7769e7f4b..5e1ba4fa3f79a0b61b3c11bbe0e0c4ff85585b4c 100644 (file)
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -1256,12 +1256,13 @@ static efi_status_t alloc_e820ext(u32 nr_desc, struct setup_data **e820ext,
 }
 
 static efi_status_t exit_boot(struct boot_params *boot_params,
-                             void *handle)
+                             void *handle, bool is64)
 {
        struct efi_info *efi = &boot_params->efi_info;
        unsigned long map_sz, key, desc_size;
        efi_memory_desc_t *mem_map;
        struct setup_data *e820ext;
+       const char *signature;
        __u32 e820ext_size;
        __u32 nr_desc, prev_nr_desc;
        efi_status_t status;
@@ -1295,7 +1296,9 @@ get_map:
                goto get_map; /* Allocated memory, get map again */
        }
 
-       memcpy(&efi->efi_loader_signature, EFI_LOADER_SIGNATURE, sizeof(__u32));
+       signature = is64 ? EFI64_LOADER_SIGNATURE : EFI32_LOADER_SIGNATURE;
+       memcpy(&efi->efi_loader_signature, signature, sizeof(__u32));
+
        efi->efi_systab = (unsigned long)sys_table;
        efi->efi_memdesc_size = desc_size;
        efi->efi_memdesc_version = desc_version;
@@ -1408,7 +1411,7 @@ struct boot_params *efi_main(struct efi_config *c,
                hdr->code32_start = bzimage_addr;
        }
 
-       status = exit_boot(boot_params, handle);
+       status = exit_boot(boot_params, handle, is64);
        if (status != EFI_SUCCESS)
                goto fail;
 

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index eed23c087d6ccfa4d8ed2bf916b9dfeec2ce716d..cccc05f0681c868a27487270d6085bf2ed96f419 100644 (file)
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -64,7 +64,7 @@ ENTRY(efi_pe_entry)
        pushl   %ecx
        jmp     2f              /* Skip efi_config initialization */
 
-ENTRY(efi_stub_entry)
+ENTRY(efi32_stub_entry)
        add     $0x4, %esp
        popl    %ecx
        popl    %edx

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 1bc206fa4bd0df91310b59cf247aba56e1c78243..37c741b0d2acbc5d0f3f84aa3386c20d4bde9ddf 100644 (file)
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -178,6 +178,13 @@ ENTRY(startup_32)
         */
        pushl   $__KERNEL_CS
        leal    startup_64(%ebp), %eax
+#ifdef CONFIG_EFI_MIXED
+       movl    efi32_config(%ebp), %ebx
+       cmp     $0, %ebx
+       jz      1f
+       leal    handover_entry(%ebp), %eax
+1:
+#endif
        pushl   %eax
 
        /* Enter paged protected Mode, activating Long Mode */
@@ -188,6 +195,30 @@ ENTRY(startup_32)
        lret
 ENDPROC(startup_32)
 
+#ifdef CONFIG_EFI_MIXED
+       .org 0x190
+ENTRY(efi32_stub_entry)
+       add     $0x4, %esp              /* Discard return address */
+       popl    %ecx
+       popl    %edx
+       popl    %esi
+
+       leal    (BP_scratch+4)(%esi), %esp
+       call    1f
+1:     pop     %ebp
+       subl    $1b, %ebp
+
+       movl    %ecx, efi32_config(%ebp)
+       movl    %edx, efi32_config+8(%ebp)
+       sgdtl   efi32_boot_gdt(%ebp)
+
+       leal    efi32_config(%ebp), %eax
+       movl    %eax, efi_config(%ebp)
+
+       jmp     startup_32
+ENDPROC(efi32_stub_entry)
+#endif
+
        .code64
        .org 0x200
 ENTRY(startup_64)
@@ -231,13 +262,7 @@ ENTRY(efi_pe_entry)
        mov     %rax, %rsi
        jmp     2f              /* Skip the relocation */
 
-ENTRY(efi_stub_entry)
-       movq    %rdi, efi64_config(%rip)        /* Handle */
-       movq    %rsi, efi64_config+8(%rip) /* EFI System table pointer */
-
-       leaq    efi64_config(%rip), %rax
-       movq    %rax, efi_config(%rip)
-
+handover_entry:
        call    1f
 1:     popq    %rbp
        subq    $1b, %rbp
@@ -247,7 +272,6 @@ ENTRY(efi_stub_entry)
         */
        movq    efi_config(%rip), %rax
        addq    %rbp, 88(%rax)
-       movq    %rdx, %rsi
 2:
        movq    efi_config(%rip), %rdi
        call    efi_main
@@ -336,6 +360,20 @@ preferred_addr:
        leaq    relocated(%rbx), %rax
        jmp     *%rax
 
+#ifdef CONFIG_EFI_STUB
+       .org 0x390
+ENTRY(efi64_stub_entry)
+       movq    %rdi, efi64_config(%rip)        /* Handle */
+       movq    %rsi, efi64_config+8(%rip) /* EFI System table pointer */
+
+       leaq    efi64_config(%rip), %rax
+       movq    %rax, efi_config(%rip)
+
+       movq    %rdx, %rsi
+       jmp     handover_entry
+ENDPROC(efi64_stub_entry)
+#endif
+
        .text
 relocated:
 
@@ -404,6 +442,14 @@ gdt_end:
 efi_config:
        .quad   0
 
+#ifdef CONFIG_EFI_MIXED
+       .global efi32_config
+efi32_config:
+       .fill   11,8,0
+       .quad   efi64_thunk
+       .byte   0
+#endif
+
        .global efi64_config
 efi64_config:
        .fill   11,8,0

diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
index bf262077ec92b062145d68ea4f99d9de6b03d5ba..4f07df5ac5d9f7f78014a0977a4a64014d9341b8 100644 (file)
--- a/arch/x86/boot/tools/build.c
+++ b/arch/x86/boot/tools/build.c
@@ -53,7 +53,8 @@ int is_big_kernel;
 
 #define PECOFF_RELOC_RESERVE 0x20
 
-unsigned long efi_stub_entry;
+unsigned long efi32_stub_entry;
+unsigned long efi64_stub_entry;
 unsigned long efi_pe_entry;
 unsigned long startup_64;
 
@@ -231,20 +232,26 @@ static void efi_stub_defaults(void)
        /* Defaults for old kernel */
 #ifdef CONFIG_X86_32
        efi_pe_entry = 0x10;
-       efi_stub_entry = 0x30;
 #else
        efi_pe_entry = 0x210;
-       efi_stub_entry = 0x230;
        startup_64 = 0x200;
 #endif
 }
 
 static void efi_stub_entry_update(void)
 {
-#ifdef CONFIG_X86_64 /* Yes, this is really how we defined it :( */
-       efi_stub_entry -= 0x200;
+       unsigned long addr = efi32_stub_entry;
+
+#ifdef CONFIG_X86_64
+       /* Yes, this is really how we defined it :( */
+       addr = efi64_stub_entry - 0x200;
+#endif
+
+#ifdef CONFIG_EFI_MIXED
+       if (efi32_stub_entry != addr)
+               die("32-bit and 64-bit EFI entry points do not match\n");
 #endif
-       put_unaligned_le32(efi_stub_entry, &buf[0x264]);
+       put_unaligned_le32(addr, &buf[0x264]);
 }
 
 #else
@@ -289,7 +296,8 @@ static void parse_zoffset(char *fname)
        p = (char *)buf;
 
        while (p && *p) {
-               PARSE_ZOFS(p, efi_stub_entry);
+               PARSE_ZOFS(p, efi32_stub_entry);
+               PARSE_ZOFS(p, efi64_stub_entry);
                PARSE_ZOFS(p, efi_pe_entry);
                PARSE_ZOFS(p, startup_64);
 

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 3d6b9f81cc683e63fbdac6c3243ab7069087e0cd..85856868507b057ef62056f895a0fe11a0a540a0 100644 (file)
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -19,9 +19,11 @@
  */
 #define EFI_OLD_MEMMAP         EFI_ARCH_1
 
+#define EFI32_LOADER_SIGNATURE "EL32"
+#define EFI64_LOADER_SIGNATURE "EL64"
+
 #ifdef CONFIG_X86_32
 
-#define EFI_LOADER_SIGNATURE   "EL32"
 
 extern unsigned long asmlinkage efi_call_phys(void *, ...);
 
@@ -57,8 +59,6 @@ extern unsigned long asmlinkage efi_call_phys(void *, ...);
 
 #else /* !CONFIG_X86_32 */
 
-#define EFI_LOADER_SIGNATURE   "EL64"
-
 extern u64 efi_call0(void *fp);
 extern u64 efi_call1(void *fp, u64 arg1);
 extern u64 efi_call2(void *fp, u64 arg1, u64 arg2);