Commit b1994304 authored by Matt Fleming's avatar Matt Fleming Committed by H. Peter Anvin
Browse files

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: default avatarMatt Fleming <matt.hfleming@intel.com>
Link: http://lkml.kernel.org/r/1334584744.26997.14.camel@mfleming-mobl1.ger.corp.intel.com


Reported-by: default avatarJordan Justen <jordan.l.justen@intel.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
Cc: <stable@vger.kernel.org> v3.3
parent d7de8649

arch/x86/boot/compressed/head_32.S

+11 −3
Original line number Diff line number Diff line
@@ -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

arch/x86/boot/compressed/head_64.S

+16 −6
Original line number Diff line number Diff line
@@ -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

arch/x86/boot/tools/build.c

+11 −4
Original line number Diff line number Diff line
@@ -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]);

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