x86, efi: Add dedicated EFI stub entry point

The method used to work out whether we were booted by EFI firmware or
via a boot loader is broken. Because efi_main() is always executed
when booting from a boot loader we will dereference invalid pointers
either on the stack (CONFIG_X86_32) or contained in %rdx
(CONFIG_X86_64) when searching for an EFI System Table signature.

Instead of dereferencing these invalid system table pointers, add a
new entry point that is only used when booting from EFI firmware, when
we know the pointer arguments will be valid. With this change legacy
boot loaders will no longer execute efi_main(), but will instead skip
EFI stub initialisation completely.

[ hpa: Marking this for urgent/stable since it is a regression when
  the option is enabled; without the option the patch has no effect ]

Signed-off-by: Matt Fleming <matt.hfleming@intel.com>
Link: http://lkml.kernel.org/r/1334584744.26997.14.camel@mfleming-mobl1.ger.corp.intel.com
Reported-by: Jordan Justen <jordan.l.justen@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: <stable@vger.kernel.org> v3.3

diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index a0559930a180ecb810df4b186d173d6fb11e3755..c85e3ac99bbabc597d772cb85b4efd4d4b3bc291 100644 (file)
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -33,6 +33,9 @@
        __HEAD
 ENTRY(startup_32)
 #ifdef CONFIG_EFI_STUB
+       jmp     preferred_addr
+
+       .balign 0x10
        /*
         * We don't need the return address, so set up the stack so
         * efi_main() can find its arugments.
@@ -41,12 +44,17 @@ ENTRY(startup_32)
 
        call    efi_main
        cmpl    $0, %eax
-       je      preferred_addr
        movl    %eax, %esi
-       call    1f
+       jne     2f
 1:
+       /* EFI init failed, so hang. */
+       hlt
+       jmp     1b
+2:
+       call    3f
+3:
        popl    %eax
-       subl    $1b, %eax
+       subl    $3b, %eax
        subl    BP_pref_address(%esi), %eax
        add     BP_code32_start(%esi), %eax
        leal    preferred_addr(%eax), %eax

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 558d76ce23bcf3518a4c9b32bced0ef717be000e..87e03a13d8e3f5d9eaad2d515679d97887833ea2 100644 (file)
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -200,18 +200,28 @@ ENTRY(startup_64)
         * entire text+data+bss and hopefully all of memory.
         */
 #ifdef CONFIG_EFI_STUB
-       pushq   %rsi
+       /*
+        * The entry point for the PE/COFF executable is 0x210, so only
+        * legacy boot loaders will execute this jmp.
+        */
+       jmp     preferred_addr
+
+       .org 0x210
        mov     %rcx, %rdi
        mov     %rdx, %rsi
        call    efi_main
-       popq    %rsi
-       cmpq    $0,%rax
-       je      preferred_addr
        movq    %rax,%rsi
-       call    1f
+       cmpq    $0,%rax
+       jne     2f
 1:
+       /* EFI init failed, so hang. */
+       hlt
+       jmp     1b
+2:
+       call    3f
+3:
        popq    %rax
-       subq    $1b, %rax
+       subq    $3b, %rax
        subq    BP_pref_address(%rsi), %rax
        add     BP_code32_start(%esi), %eax
        leaq    preferred_addr(%rax), %rax

diff --git a/arch/x86/boot/tools/build.c b/arch/x86/boot/tools/build.c
index ed549767a231eece626dd19cd64746cb2569b6f5..24443a3320838ede8cdf995525851794e8d1052a 100644 (file)
--- a/arch/x86/boot/tools/build.c
+++ b/arch/x86/boot/tools/build.c
@@ -205,8 +205,13 @@ int main(int argc, char ** argv)
        put_unaligned_le32(file_sz, &buf[pe_header + 0x50]);
 
 #ifdef CONFIG_X86_32
-       /* Address of entry point */
-       put_unaligned_le32(i, &buf[pe_header + 0x28]);
+       /*
+        * Address of entry point.
+        *
+        * The EFI stub entry point is +16 bytes from the start of
+        * the .text section.
+        */
+       put_unaligned_le32(i + 16, &buf[pe_header + 0x28]);
 
        /* .text size */
        put_unaligned_le32(file_sz, &buf[pe_header + 0xb0]);
@@ -217,9 +222,11 @@ int main(int argc, char ** argv)
        /*
         * Address of entry point. startup_32 is at the beginning and
         * the 64-bit entry point (startup_64) is always 512 bytes
-        * after.
+        * after. The EFI stub entry point is 16 bytes after that, as
+        * the first instruction allows legacy loaders to jump over
+        * the EFI stub initialisation
         */
-       put_unaligned_le32(i + 512, &buf[pe_header + 0x28]);
+       put_unaligned_le32(i + 528, &buf[pe_header + 0x28]);
 
        /* .text size */
        put_unaligned_le32(file_sz, &buf[pe_header + 0xc0]);