linux-hwg/0007-x86-efi-Correct-EFI-boot-stub-use-of-code32_start.patch

From 720a9dbf61c88bd57d6f8198ed8ccb2bd4a6abd8 Mon Sep 17 00:00:00 2001
From: Matt Fleming <matt@console-pimps.org>
Date: Wed, 9 Apr 2014 10:33:49 +0200
Subject: [PATCH 07/10] x86/efi: Correct EFI boot stub use of code32_start
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code32_start should point at the start of the protected mode code, and
*not* at the beginning of the bzImage. This is much easier to do in
assembly so document that callers of make_boot_params() need to fill out
code32_start.

The fallout from this bug is that we would end up relocating the image
but copying the image at some offset, resulting in what appeared to be
memory corruption.

Reported-by: Thomas Bächler <thomas@archlinux.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
---
 arch/x86/boot/compressed/eboot.c   |  5 +++--
 arch/x86/boot/compressed/head_32.S | 14 ++++++++------
 arch/x86/boot/compressed/head_64.S |  9 +++------
 3 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index a7677ba..78cbb2d 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -425,6 +425,9 @@ void setup_graphics(struct boot_params *boot_params)
  * Because the x86 boot code expects to be passed a boot_params we
  * need to create one ourselves (usually the bootloader would create
  * one for us).
+ *
+ * The caller is responsible for filling out ->code32_start in the
+ * returned boot_params.
  */
 struct boot_params *make_boot_params(void *handle, efi_system_table_t *_table)
 {
@@ -483,8 +486,6 @@ struct boot_params *make_boot_params(void *handle, efi_system_table_t *_table)
 	hdr->vid_mode = 0xffff;
 	hdr->boot_flag = 0xAA55;
 
-	hdr->code32_start = (__u64)(unsigned long)image->image_base;
-
 	hdr->type_of_loader = 0x21;
 
 	/* Convert unicode cmdline to ascii */
diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 9116aac..f45ab7a 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -50,6 +50,13 @@ ENTRY(efi_pe_entry)
 	pushl	%eax
 	pushl	%esi
 	pushl	%ecx
+
+	call	reloc
+reloc:
+	popl	%ecx
+	subl	reloc, %ecx
+	movl	%ecx, BP_code32_start(%eax)
+
 	sub	$0x4, %esp
 
 ENTRY(efi_stub_entry)
@@ -63,12 +70,7 @@ ENTRY(efi_stub_entry)
 	hlt
 	jmp	1b
 2:
-	call	3f
-3:
-	popl	%eax
-	subl	$3b, %eax
-	subl	BP_pref_address(%esi), %eax
-	add	BP_code32_start(%esi), %eax
+	movl	BP_code32_start(%esi), %eax
 	leal	preferred_addr(%eax), %eax
 	jmp	*%eax
 
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index c5c1ae0..b10fa66 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -217,6 +217,8 @@ ENTRY(efi_pe_entry)
 	cmpq	$0,%rax
 	je	1f
 	mov	%rax, %rdx
+	leaq	startup_32(%rip), %rax
+	movl	%eax, BP_code32_start(%rdx)
 	popq	%rsi
 	popq	%rdi
 
@@ -230,12 +232,7 @@ ENTRY(efi_stub_entry)
 	hlt
 	jmp	1b
 2:
-	call	3f
-3:
-	popq	%rax
-	subq	$3b, %rax
-	subq	BP_pref_address(%rsi), %rax
-	add	BP_code32_start(%esi), %eax
+	movl	BP_code32_start(%esi), %eax
 	leaq	preferred_addr(%rax), %rax
 	jmp	*%rax
 
-- 
1.9.2