Patchwork [U-Boot,v2,7/9] x86: Add error checking to x86 relocation code

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Submitter Simon Glass
Date March 1, 2013, 5:26 a.m.
Message ID <1362115578-12165-7-git-send-email-sjg@chromium.org>
Download mbox | patch
Permalink /patch/224234/
State Accepted, archived
Delegated to: Simon Glass
Headers show

Comments

Simon Glass - March 1, 2013, 5:26 a.m.
This does not actually change normal behaviour, but adds a check that
should detect corruption of relocation data (e.g. by using BSS data
prior to relocation).

Also add additional debugging output when enabled.

During this investigation, two situations have been seen:
1. calculate_relocation_address():
	uintptr_t size = (uintptr_t)&__bss_end - (uintptr_t)&__text_start;

turns into
     111166f:	b8 83 c4 17 01       	mov    $0x117c483,%eax

whih is beyond the end of bss:

0117b484 g       .bss	00000000 __bss_end

Somehow the __bss_end here is 255 bytes ahead.

2. do_elf_reloc_fixups():

	uintptr_t size = (uintptr_t)&__bss_end - (uintptr_t)&__text_start;

Here the __text_start is 0 in the file:

 1111d9f:	bb a0 e0 13 01       	mov    $0x113e0a0,%ebx
1111da4:	81 ef 00 00 00 00    	sub    $0x0,%edi

As it happens, both of these are in pre-relocation code.

For these reasons we silent check and ignore bad relocations.

Signed-off-by: Simon Glass <sjg@chromium.org>
---
Changes in v2: None

 arch/x86/lib/relocate.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

Patch

diff --git a/arch/x86/lib/relocate.c b/arch/x86/lib/relocate.c
index 3a38e52..3e370f2 100644
--- a/arch/x86/lib/relocate.c
+++ b/arch/x86/lib/relocate.c
@@ -73,12 +73,16 @@  int clear_bss(void)
 	return 0;
 }
 
+/*
+ * This function has more error checking than you might expect. Please see
+ * the commit message for more informaiton.
+ */
 int do_elf_reloc_fixups(void)
 {
 	Elf32_Rel *re_src = (Elf32_Rel *)(&__rel_dyn_start);
 	Elf32_Rel *re_end = (Elf32_Rel *)(&__rel_dyn_end);
 
-	Elf32_Addr *offset_ptr_rom;
+	Elf32_Addr *offset_ptr_rom, *last_offset = NULL;
 	Elf32_Addr *offset_ptr_ram;
 
 	/* The size of the region of u-boot that runs out of RAM. */
@@ -89,7 +93,8 @@  int do_elf_reloc_fixups(void)
 		offset_ptr_rom = (Elf32_Addr *)re_src->r_offset;
 
 		/* Check that the location of the relocation is in .text */
-		if (offset_ptr_rom >= (Elf32_Addr *)CONFIG_SYS_TEXT_BASE) {
+		if (offset_ptr_rom >= (Elf32_Addr *)CONFIG_SYS_TEXT_BASE &&
+				offset_ptr_rom > last_offset) {
 
 			/* Switch to the in-RAM version */
 			offset_ptr_ram = (Elf32_Addr *)((ulong)offset_ptr_rom +
@@ -100,8 +105,19 @@  int do_elf_reloc_fixups(void)
 					*offset_ptr_ram <=
 					(CONFIG_SYS_TEXT_BASE + size)) {
 				*offset_ptr_ram += gd->reloc_off;
+			} else {
+				debug("   %p: rom reloc %x, ram %p, value %x,"
+					" limit %lx\n", re_src,
+					re_src->r_offset, offset_ptr_ram,
+					*offset_ptr_ram,
+					CONFIG_SYS_TEXT_BASE + size);
 			}
+		} else {
+			debug("   %p: rom reloc %x, last %p\n", re_src,
+			       re_src->r_offset, last_offset);
 		}
+		last_offset = offset_ptr_rom;
+
 	} while (++re_src < re_end);
 
 	return 0;