cbfstool: Fix segmentation fault for data segment relocation

`cbfstool add-stage' crashes with a segmentation fault when generating
the program binary out of a romstage ELF containing relocation within
the data segment.

This commit makes `parse_elf_to_xip_stage()' look for the segment to
which the current relocation applies and compute the appropriate
location within the program binary.

This issue can be reproduced by defining a global variable with a
pointer to constant data. This variable is defined within the .data
section and contains a pointer to a constant which resides in the
.text section. As a result, a relocation entry is generated in the ELF
file.

    struct my_struct {
            const char *name;
    };

    struct my_struct my_global = { .name = "EXAMPLE" };

    void fun(void)
    {
           printk(BIOS_DEBUG, "my_global.name=%s\n", my_global.name);
    }

TEST=global data structure with a pointer to a constant does not make
     cbfstool crash

Change-Id: I480b4b047546c8aa4e12dfb688e0299f80283235
Signed-off-by: Jeremy Compostella <jeremy.compostella@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/84864
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Shuo Liu <shuo.liu@intel.com>
Reviewed-by: Wonkyu Kim <wonkyu.kim@intel.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/util/cbfstool/cbfs-mkstage.c b/util/cbfstool/cbfs-mkstage.c
index 2338adc7ae..a72b387c2b 100644
--- a/util/cbfstool/cbfs-mkstage.c
+++ b/util/cbfstool/cbfs-mkstage.c
@@ -403,11 +403,23 @@ int parse_elf_to_xip_stage(const struct buffer *input, struct buffer *output,
 		size_t reloc_offset;
 		uint32_t val;
 		struct buffer in, out;
+		Elf64_Addr reloc = rmodctx->emitted_relocs[i];
 
 		/* The relocations represent in-program addresses of the
 		 * linked program. Obtain the offset into the program to do
 		 * the adjustment. */
-		reloc_offset = rmodctx->emitted_relocs[i] - pelf->phdr->p_vaddr;
+		reloc_offset = 0;
+		for (phdr = toload; *phdr; phdr++) {
+			if (reloc >= (*phdr)->p_vaddr &&
+			    reloc < (*phdr)->p_vaddr + (*phdr)->p_memsz)
+				break;
+			reloc_offset += (*phdr)->p_filesz;
+		}
+		if (!*phdr) {
+			ERROR("Relocation outside of loadable segments\n");
+			goto out;
+		}
+		reloc_offset += reloc - (*phdr)->p_vaddr;
 
 		buffer_clone(&out, &boutput);
 		buffer_seek(&out, reloc_offset);