x86/efi: Correct EFI boot stub use of code32_start

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>

3 files changed, 8 insertions, 14 deletions

diff --git a/arch/x86/boot/compressed/eboot.c b/arch/x86/boot/compressed/eboot.c
index 280165524ee4..91d17007323b 100644
--- a/arch/x86/boot/compressed/eboot.c
+++ b/arch/x86/boot/compressed/eboot.c
@@ -1016,6 +1016,9 @@ 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(struct efi_config *c)
 {
@@ -1081,8 +1084,6 @@ struct boot_params *make_boot_params(struct efi_config *c)
         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 de9d4200d305..cbed1407a5cd 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -59,6 +59,7 @@ ENTRY(efi_pe_entry)
         call    make_boot_params
         cmpl    $0, %eax
         je      fail
+        movl    %esi, BP_code32_start(%eax)
         popl    %ecx
         pushl   %eax
         pushl   %ecx
@@ -90,12 +91,7 @@ fail:
         hlt
         jmp     fail
 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 57e58a5fa210..0d558ee899ae 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -261,6 +261,8 @@ ENTRY(efi_pe_entry)
         cmpq    $0,%rax
         je      fail
         mov     %rax, %rsi
+        leaq    startup_32(%rip), %rax
+        movl    %eax, BP_code32_start(%rsi)
         jmp     2f              /* Skip the relocation */
 
 handover_entry:
@@ -284,12 +286,7 @@ fail:
         hlt
         jmp     fail
 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