x86/efi: Fixup GOT in all boot code paths

Maarten reported that his Macbook pro 8.2 stopped booting after commit
f23cf8bd5c1f49 ("efi/x86: efistub: Move shared dependencies to
<asm/efi.h>"), the main feature of which is changing the visibility of
symbol 'efi_early' from local to global.

By making 'efi_early' global we end up requiring an entry in the Global
Offset Table. Unfortunately, while we do include code to fixup GOT
entries in the early boot code, it's only called after we've executed
the EFI boot stub.

What this amounts to is that references to 'efi_early' in the EFI boot
stub don't point to the correct place.

Since we've got multiple boot entry points we need to be prepared to
fixup the GOT in multiple places, while ensuring that we never do it
more than once, otherwise the GOT entries will still point to the wrong
place.

Reported-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Tested-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

2 files changed, 81 insertions, 29 deletions

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index cbed1407a5cd..d6b8aa4c986c 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -30,6 +30,33 @@
 #include <asm/boot.h>
 #include <asm/asm-offsets.h>
 
+/*
+ * Adjust our own GOT
+ *
+ * The relocation base must be in %ebx
+ *
+ * It is safe to call this macro more than once, because in some of the
+ * code paths multiple invocations are inevitable, e.g. via the efi*
+ * entry points.
+ *
+ * Relocation is only performed the first time.
+ */
+.macro FIXUP_GOT
+        cmpb    $1, got_fixed(%ebx)
+        je      2f
+
+        leal    _got(%ebx), %edx
+        leal    _egot(%ebx), %ecx
+1:
+        cmpl    %ecx, %edx
+        jae     2f
+        addl    %ebx, (%edx)
+        addl    $4, %edx
+        jmp     1b
+2:
+        movb    $1, got_fixed(%ebx)
+.endm
+
         __HEAD
 ENTRY(startup_32)
 #ifdef CONFIG_EFI_STUB
@@ -56,6 +83,9 @@ ENTRY(efi_pe_entry)
         add     %esi, 88(%eax)
         pushl   %eax
 
+        movl    %esi, %ebx
+        FIXUP_GOT
+
         call    make_boot_params
         cmpl    $0, %eax
         je      fail
@@ -81,6 +111,10 @@ ENTRY(efi32_stub_entry)
         leal    efi32_config(%esi), %eax
         add     %esi, 88(%eax)
         pushl   %eax
+
+        movl    %esi, %ebx
+        FIXUP_GOT
+
 2:
         call    efi_main
         cmpl    $0, %eax
@@ -190,19 +224,7 @@ relocated:
         shrl    $2, %ecx
         rep     stosl
 
-/*
- * Adjust our own GOT
- */
-        leal    _got(%ebx), %edx
-        leal    _egot(%ebx), %ecx
-1:
-        cmpl    %ecx, %edx
-        jae     2f
-        addl    %ebx, (%edx)
-        addl    $4, %edx
-        jmp     1b
-2:
-
+        FIXUP_GOT
 /*
  * Do the decompression, and jump to the new kernel..
  */
@@ -225,8 +247,12 @@ relocated:
         xorl    %ebx, %ebx
         jmp     *%eax
 
-#ifdef CONFIG_EFI_STUB
         .data
+/* Have we relocated the GOT? */
+got_fixed:
+        .byte 0
+
+#ifdef CONFIG_EFI_STUB
 efi32_config:
         .fill 11,8,0
         .long efi_call_phys
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 2884e0c3e8a5..50f69c7eaaf4 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -32,6 +32,33 @@
 #include <asm/processor-flags.h>
 #include <asm/asm-offsets.h>
 
+/*
+ * Adjust our own GOT
+ *
+ * The relocation base must be in %rbx
+ *
+ * It is safe to call this macro more than once, because in some of the
+ * code paths multiple invocations are inevitable, e.g. via the efi*
+ * entry points.
+ *
+ * Relocation is only performed the first time.
+ */
+.macro FIXUP_GOT
+        cmpb    $1, got_fixed(%rip)
+        je      2f
+
+        leaq    _got(%rip), %rdx
+        leaq    _egot(%rip), %rcx
+1:
+        cmpq    %rcx, %rdx
+        jae     2f
+        addq    %rbx, (%rdx)
+        addq    $8, %rdx
+        jmp     1b
+2:
+        movb    $1, got_fixed(%rip)
+.endm
+
         __HEAD
         .code32
 ENTRY(startup_32)
@@ -252,10 +279,13 @@ ENTRY(efi_pe_entry)
         subq    $1b, %rbp
 
         /*
-         * Relocate efi_config->call().
+         * Relocate efi_config->call() and the GOT entries.
          */
         addq    %rbp, efi64_config+88(%rip)
 
+        movq    %rbp, %rbx
+        FIXUP_GOT
+
         movq    %rax, %rdi
         call    make_boot_params
         cmpq    $0,%rax
@@ -271,10 +301,13 @@ handover_entry:
         subq    $1b, %rbp
 
         /*
-         * Relocate efi_config->call().
+         * Relocate efi_config->call() and the GOT entries.
          */
         movq    efi_config(%rip), %rax
         addq    %rbp, 88(%rax)
+
+        movq    %rbp, %rbx
+        FIXUP_GOT
 2:
         movq    efi_config(%rip), %rdi
         call    efi_main
@@ -385,19 +418,8 @@ relocated:
         shrq    $3, %rcx
         rep     stosq
 
-/*
- * Adjust our own GOT
- */
-        leaq    _got(%rip), %rdx
-        leaq    _egot(%rip), %rcx
-1:
-        cmpq    %rcx, %rdx
-        jae     2f
-        addq    %rbx, (%rdx)
-        addq    $8, %rdx
-        jmp     1b
-2:
-        
+        FIXUP_GOT
+
 /*
  * Do the decompression, and jump to the new kernel..
  */
@@ -437,6 +459,10 @@ gdt:
         .quad   0x0000000000000000      /* TS continued */
 gdt_end:
 
+/* Have we relocated the GOT? */
+got_fixed:
+        .byte   0
+
 #ifdef CONFIG_EFI_STUB
 efi_config:
         .quad   0