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Subject[PATCH v2] x86/tools/relocs: fix big section header tables
Date
In case when the number of entries in the section header table is larger
then or equal to SHN_LORESERVE the size of the table is held in the sh_size
member of the initial entry in section header table instead of e_shnum.
Same with the string table index which is located in sh_link instead of
e_shstrndx.

This case is easily reproducible with KCFLAGS="-ffunction-sections",
bzImage build fails with "String table index out of bounds" error.

Signed-off-by: Artem Savkov <asavkov@redhat.com>
---
arch/x86/tools/relocs.c | 58 +++++++++++++++++++++++++++++------------
1 file changed, 41 insertions(+), 17 deletions(-)

diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index b629f6992d9f..1f5dcec15d4e 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -11,7 +11,9 @@
#define Elf_Shdr ElfW(Shdr)
#define Elf_Sym ElfW(Sym)

-static Elf_Ehdr ehdr;
+static Elf_Ehdr ehdr;
+static unsigned long shnum;
+static unsigned int shstrndx;

struct relocs {
uint32_t *offset;
@@ -241,9 +243,9 @@ static const char *sec_name(unsigned shndx)
{
const char *sec_strtab;
const char *name;
- sec_strtab = secs[ehdr.e_shstrndx].strtab;
+ sec_strtab = secs[shstrndx].strtab;
name = "<noname>";
- if (shndx < ehdr.e_shnum) {
+ if (shndx < shnum) {
name = sec_strtab + secs[shndx].shdr.sh_name;
}
else if (shndx == SHN_ABS) {
@@ -271,7 +273,7 @@ static const char *sym_name(const char *sym_strtab, Elf_Sym *sym)
static Elf_Sym *sym_lookup(const char *symname)
{
int i;
- for (i = 0; i < ehdr.e_shnum; i++) {
+ for (i = 0; i < shnum; i++) {
struct section *sec = &secs[i];
long nsyms;
char *strtab;
@@ -366,6 +368,9 @@ static void read_ehdr(FILE *fp)
ehdr.e_shnum = elf_half_to_cpu(ehdr.e_shnum);
ehdr.e_shstrndx = elf_half_to_cpu(ehdr.e_shstrndx);

+ shnum = ehdr.e_shnum;
+ shstrndx = ehdr.e_shstrndx;
+
if ((ehdr.e_type != ET_EXEC) && (ehdr.e_type != ET_DYN)) {
die("Unsupported ELF header type\n");
}
@@ -384,7 +389,26 @@ static void read_ehdr(FILE *fp)
if (ehdr.e_shentsize != sizeof(Elf_Shdr)) {
die("Bad section header entry\n");
}
- if (ehdr.e_shstrndx >= ehdr.e_shnum) {
+
+ if (shnum == SHN_UNDEF || shstrndx == SHN_XINDEX) {
+ Elf_Shdr shdr;
+
+ if (fseek(fp, ehdr.e_shoff, SEEK_SET) < 0)
+ die("Seek to %d failed: %s\n",
+ ehdr.e_shoff, strerror(errno));
+
+ if (fread(&shdr, sizeof(shdr), 1, fp) != 1)
+ die("Cannot read initial ELF section header: %s\n",
+ strerror(errno));
+
+ if (shnum == SHN_UNDEF)
+ shnum = elf_xword_to_cpu(shdr.sh_size);
+
+ if (shstrndx == SHN_XINDEX)
+ shstrndx = elf_word_to_cpu(shdr.sh_link);
+ }
+
+ if (shstrndx >= shnum) {
die("String table index out of bounds\n");
}
}
@@ -394,20 +418,20 @@ static void read_shdrs(FILE *fp)
int i;
Elf_Shdr shdr;

- secs = calloc(ehdr.e_shnum, sizeof(struct section));
+ secs = calloc(shnum, sizeof(struct section));
if (!secs) {
die("Unable to allocate %d section headers\n",
- ehdr.e_shnum);
+ shnum);
}
if (fseek(fp, ehdr.e_shoff, SEEK_SET) < 0) {
die("Seek to %d failed: %s\n",
ehdr.e_shoff, strerror(errno));
}
- for (i = 0; i < ehdr.e_shnum; i++) {
+ for (i = 0; i < shnum; i++) {
struct section *sec = &secs[i];
if (fread(&shdr, sizeof(shdr), 1, fp) != 1)
die("Cannot read ELF section headers %d/%d: %s\n",
- i, ehdr.e_shnum, strerror(errno));
+ i, shnum, strerror(errno));
sec->shdr.sh_name = elf_word_to_cpu(shdr.sh_name);
sec->shdr.sh_type = elf_word_to_cpu(shdr.sh_type);
sec->shdr.sh_flags = elf_xword_to_cpu(shdr.sh_flags);
@@ -418,7 +442,7 @@ static void read_shdrs(FILE *fp)
sec->shdr.sh_info = elf_word_to_cpu(shdr.sh_info);
sec->shdr.sh_addralign = elf_xword_to_cpu(shdr.sh_addralign);
sec->shdr.sh_entsize = elf_xword_to_cpu(shdr.sh_entsize);
- if (sec->shdr.sh_link < ehdr.e_shnum)
+ if (sec->shdr.sh_link < shnum)
sec->link = &secs[sec->shdr.sh_link];
}

@@ -427,7 +451,7 @@ static void read_shdrs(FILE *fp)
static void read_strtabs(FILE *fp)
{
int i;
- for (i = 0; i < ehdr.e_shnum; i++) {
+ for (i = 0; i < shnum; i++) {
struct section *sec = &secs[i];
if (sec->shdr.sh_type != SHT_STRTAB) {
continue;
@@ -452,7 +476,7 @@ static void read_strtabs(FILE *fp)
static void read_symtabs(FILE *fp)
{
int i,j;
- for (i = 0; i < ehdr.e_shnum; i++) {
+ for (i = 0; i < shnum; i++) {
struct section *sec = &secs[i];
if (sec->shdr.sh_type != SHT_SYMTAB) {
continue;
@@ -485,7 +509,7 @@ static void read_symtabs(FILE *fp)
static void read_relocs(FILE *fp)
{
int i,j;
- for (i = 0; i < ehdr.e_shnum; i++) {
+ for (i = 0; i < shnum; i++) {
struct section *sec = &secs[i];
if (sec->shdr.sh_type != SHT_REL_TYPE) {
continue;
@@ -528,7 +552,7 @@ static void print_absolute_symbols(void)

printf("Absolute symbols\n");
printf(" Num: Value Size Type Bind Visibility Name\n");
- for (i = 0; i < ehdr.e_shnum; i++) {
+ for (i = 0; i < shnum; i++) {
struct section *sec = &secs[i];
char *sym_strtab;
int j;
@@ -566,7 +590,7 @@ static void print_absolute_relocs(void)
else
format = "%08"PRIx32" %08"PRIx32" %10s %08"PRIx32" %s\n";

- for (i = 0; i < ehdr.e_shnum; i++) {
+ for (i = 0; i < shnum; i++) {
struct section *sec = &secs[i];
struct section *sec_applies, *sec_symtab;
char *sym_strtab;
@@ -650,7 +674,7 @@ static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel,
{
int i;
/* Walk through the relocations */
- for (i = 0; i < ehdr.e_shnum; i++) {
+ for (i = 0; i < shnum; i++) {
char *sym_strtab;
Elf_Sym *sh_symtab;
struct section *sec_applies, *sec_symtab;
@@ -706,7 +730,7 @@ static Elf_Addr per_cpu_load_addr;
static void percpu_init(void)
{
int i;
- for (i = 0; i < ehdr.e_shnum; i++) {
+ for (i = 0; i < shnum; i++) {
ElfW(Sym) *sym;
if (strcmp(sec_name(i), ".data..percpu"))
continue;
--
2.19.1
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