[PATCH 1/2] modpost: fix potential segmentation fault for addend_i386_rel()

From: Masahiro Yamada
Date: Mon May 25 2020 - 01:47:40 EST

This may not be a practical problem, but the second pass of ARCH=i386
modpost causes segmentation fault if the -s option is not passed.

MODPOST 12 modules
Segmentation fault (core dumped)
make[2]: *** [scripts/Makefile.modpost:94: __modpost] Error 139
make[1]: *** [Makefile:1339: modules] Error 2
make[1]: *** Waiting for unfinished jobs....

The segmentation fault occurs when section_rel() is called for vmlinux,
which is untested in regular builds. The cause of the problem is
reloc_location() returns a wrong pointer for ET_EXEC object type.
In this case, you need to subtract sechdr->sh_addr, otherwise it would
get access beyond the mmap'ed memory.

Add sym_get_data_offset() helper to avoid code duplication.

Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>

scripts/mod/modpost.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 34f2aa3a021f..a8306adb3554 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -345,19 +345,23 @@ static const char *sec_name(struct elf_info *elf, int secindex)
return sech_name(elf, &elf->sechdrs[secindex]);

-static void *sym_get_data(const struct elf_info *info, const Elf_Sym *sym)
+static void *sym_get_data_offset(const struct elf_info *info,
+ unsigned int secindex, unsigned long offset)
- unsigned int secindex = get_secindex(info, sym);
Elf_Shdr *sechdr = &info->sechdrs[secindex];
- unsigned long offset;

- offset = sym->st_value;
if (info->hdr->e_type != ET_REL)
offset -= sechdr->sh_addr;

return (void *)info->hdr + sechdr->sh_offset + offset;

+static void *sym_get_data(const struct elf_info *info, const Elf_Sym *sym)
+ return sym_get_data_offset(info, get_secindex(info, sym),
+ sym->st_value);
#define strstarts(str, prefix) (strncmp(str, prefix, strlen(prefix)) == 0)

static enum export export_from_secname(struct elf_info *elf, unsigned int sec)
@@ -1761,11 +1765,7 @@ static void check_section_mismatch(const char *modname, struct elf_info *elf,
static unsigned int *reloc_location(struct elf_info *elf,
Elf_Shdr *sechdr, Elf_Rela *r)
- Elf_Shdr *sechdrs = elf->sechdrs;
- int section = sechdr->sh_info;
- return (void *)elf->hdr + sechdrs[section].sh_offset +
- r->r_offset;
+ return sym_get_data_offset(elf, sechdr->sh_info, r->r_offset);

static int addend_386_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)