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From:   Jan Stancek <jstancek@redhat.com>
To:     luto@mit.edu
Cc:     hpa@linux.intel.com, linux-kernel@vger.kernel.org,
        jstancek@redhat.com
Subject: [PATCH RESEND] selftests: vdso: hash entry size on alpha,s390x is 8 bytes
Date:   Mon,  3 Aug 2020 14:52:15 +0200
Message-Id: <93a07b1808e61babef3a20542cbeb4565d3c8410.1596458924.git.jstancek@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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(-)

Resend with original author CC-ed.

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