[LTP] [PATCH] selftests: vdso: hash entry size on alpha, s390x is 8 bytes

Jan Stancek
2020-07-15T11:07:11Z

parse_vdso.c is crashing on 5.8-rc5 s390x, because it wrongly reads
nbucket as 0:
Program received signal SIGFPE, Arithmetic exception.
0x0000000001000f3e in vdso_sym (version=0x1001280 "LINUX_2.6", name=0x100128a "__vdso_getcpu") at parse_vdso.c:207
207 ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
(gdb) p vdso_info.nbucket
$1 = 0

Per readelf source:
https://sourceware.org/git/?p=binutils-gdb.git;a=blob;f=binutils/readelf.c;h=2406304fe35a832ac53aa7b1a367f3f7afed4264;hb=HEAD#l10027
and objdump output hash entries are double size on 64bit s390 and alpha:
0000000000000120 <.hash>:
120: 00 00 00 00 .long 0x00000000
124: 00 00 00 03 .long 0x00000003
128: 00 00 00 00 .long 0x00000000
12c: 00 00 00 07 .long 0x00000007
130: 00 00 00 00 .long 0x00000000
134: 00 00 00 01 .long 0x00000001
138: 00 00 00 00 .long 0x00000000
13c: 00 00 00 05 .long 0x00000005
140: 00 00 00 00 .long 0x00000000
144: 00 00 00 06 .long 0x00000006
...
16c: 00 00 00 02 .long 0x00000002
170: 00 00 00 00 .long 0x00000000
174: 00 00 00 03 .long 0x00000003
178: 00 00 00 00 .long 0x00000000
17c: 00 00 00 04 .long 0x00000004

Do similar check in parse_vdso.c and treat hash entries as double word.

Signed-off-by: Jan Stancek <jstancek@redhat.com>
---
tools/testing/selftests/vDSO/parse_vdso.c | 48 +++++++++++++++++++----
1 file changed, 40 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/vDSO/parse_vdso.c b/tools/testing/selftests/vDSO/parse_vdso.c
index 413f75620a35..e23efcbd1c88 100644
--- a/tools/testing/selftests/vDSO/parse_vdso.c
+++ b/tools/testing/selftests/vDSO/parse_vdso.c
@@ -47,8 +47,9 @@ static struct vdso_info
/* Symbol table */
ELF(Sym) *symtab;
const char *symstrings;
- ELF(Word) *bucket, *chain;
+ void *bucket, *chain;
ELF(Word) nbucket, nchain;
+ bool hash_ent_is_dword;

/* Version table */
ELF(Versym) *versym;
@@ -69,6 +70,28 @@ static unsigned long elf_hash(const unsigned char *name)
return h;
}

+/* return value of hash table entry */
+ELF(Word) get_hash_val(void *ptr, ELF(Word) idx)
+{
+ if (vdso_info.hash_ent_is_dword) {
+ ELF(Xword) *table = ptr;
+ /* for vdso assume all values fit in Elf Word */
+ return (ELF(Word)) table[idx];
+ }
+
+ ELF(Word) *table = ptr;
+ return table[idx];
+}
+
+/* return pointer to hash table entry */
+void *get_hash_ptr(void *ptr, ELF(Word) idx)
+{
+ if (vdso_info.hash_ent_is_dword)
+ return &((ELF(Xword) *) ptr)[idx];
+
+ return &((ELF(Word) *) ptr)[idx];
+}
+
void vdso_init_from_sysinfo_ehdr(uintptr_t base)
{
size_t i;
@@ -84,6 +107,14 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)
return; /* Wrong ELF class -- check ELF_BITS */
}

+ /* 64bit s390 and alpha have hash entry size of 8 bytes */
+ if ((hdr->e_machine == EM_ALPHA
+ || hdr->e_machine == EM_S390)
+ && hdr->e_ident[EI_CLASS] == ELFCLASS64)
+ vdso_info.hash_ent_is_dword = true;
+ else
+ vdso_info.hash_ent_is_dword = false;
+
ELF(Phdr) *pt = (ELF(Phdr)*)(vdso_info.load_addr + hdr->e_phoff);
ELF(Dyn) *dyn = 0;

@@ -149,11 +180,11 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base)
if (!vdso_info.verdef)
vdso_info.versym = 0;

- /* Parse the hash table header. */
- vdso_info.nbucket = hash[0];
- vdso_info.nchain = hash[1];
- vdso_info.bucket = &hash[2];
- vdso_info.chain = &hash[vdso_info.nbucket + 2];
+
+ vdso_info.nbucket = get_hash_val(hash, 0);
+ vdso_info.nchain = get_hash_val(hash, 1);
+ vdso_info.bucket = get_hash_ptr(hash, 2);
+ vdso_info.chain = get_hash_ptr(hash, vdso_info.nbucket + 2);

/* That's all we need. */
vdso_info.valid = true;
@@ -204,9 +235,10 @@ void *vdso_sym(const char *version, const char *name)
return 0;

ver_hash = elf_hash(version);
- ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
+ ELF(Word) chain = get_hash_val(vdso_info.bucket,
+ elf_hash(name) % vdso_info.nbucket);

- for (; chain != STN_UNDEF; chain = vdso_info.chain[chain]) {
+ for (; chain != STN_UNDEF; chain = get_hash_val(vdso_info.chain, chain)) {
ELF(Sym) *sym = &vdso_info.symtab[chain];

/* Check for a defined global or weak function w/ right name. */
--
2.18.1