1 files changed, 300 insertions, 0 deletions
diff --git a/tools/testing/selftests/vDSO/parse_vdso.c b/tools/testing/selftests/vDSO/parse_vdso.c
new file mode 100644
index 000000000000..3ff00fb624a4
--- /dev/null
+++ b/tools/testing/selftests/vDSO/parse_vdso.c
@@ -0,0 +1,300 @@
+/*
+ * parse_vdso.c: Linux reference vDSO parser
+ * Written by Andrew Lutomirski, 2011-2014.
+ *
+ * This code is meant to be linked in to various programs that run on Linux.
+ * As such, it is available with as few restrictions as possible.  This file
+ * is licensed under the Creative Commons Zero License, version 1.0,
+ * available at http://creativecommons.org/publicdomain/zero/1.0/legalcode
+ *
+ * The vDSO is a regular ELF DSO that the kernel maps into user space when
+ * it starts a program.  It works equally well in statically and dynamically
+ * linked binaries.
+ *
+ * This code is tested on x86.  In principle it should work on any
+ * architecture that has a vDSO.
+ */
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+#include <limits.h>
+#include <linux/auxvec.h>
+#include <linux/elf.h>
+
+#include "parse_vdso.h"
+
+/* And here's the code. */
+#ifndef ELF_BITS
+# if __SIZEOF_LONG__ >= 8
+#  define ELF_BITS 64
+# else
+#  define ELF_BITS 32
+# endif
+#endif
+
+#define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
+#define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
+#define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)
+
+#ifdef __s390x__
+#define ELF_HASH_ENTRY ELF(Xword)
+#else
+#define ELF_HASH_ENTRY ELF(Word)
+#endif
+
+static struct vdso_info
+{
+	bool valid;
+
+	/* Load information */
+	uintptr_t load_addr;
+	uintptr_t load_offset;  /* load_addr - recorded vaddr */
+
+	/* Symbol table */
+	ELF(Sym) *symtab;
+	const char *symstrings;
+	ELF(Word) *gnu_hash, *gnu_bucket;
+	ELF_HASH_ENTRY *bucket, *chain;
+	ELF_HASH_ENTRY nbucket, nchain;
+
+	/* Version table */
+	ELF(Versym) *versym;
+	ELF(Verdef) *verdef;
+} vdso_info;
+
+/*
+ * Straight from the ELF specification...and then tweaked slightly, in order to
+ * avoid a few clang warnings.
+ */
+static unsigned long elf_hash(const char *name)
+{
+	unsigned long h = 0, g;
+	const unsigned char *uch_name = (const unsigned char *)name;
+
+	while (*uch_name)
+	{
+		h = (h << 4) + *uch_name++;
+		g = h & 0xf0000000;
+		if (g)
+			h ^= g >> 24;
+		h &= ~g;
+	}
+	return h;
+}
+
+static uint32_t gnu_hash(const char *name)
+{
+	const unsigned char *s = (void *)name;
+	uint32_t h = 5381;
+
+	for (; *s; s++)
+		h += h * 32 + *s;
+	return h;
+}
+
+void vdso_init_from_sysinfo_ehdr(uintptr_t base)
+{
+	size_t i;
+	bool found_vaddr = false;
+
+	vdso_info.valid = false;
+
+	vdso_info.load_addr = base;
+
+	ELF(Ehdr) *hdr = (ELF(Ehdr)*)base;
+	if (hdr->e_ident[EI_CLASS] !=
+	    (ELF_BITS == 32 ? ELFCLASS32 : ELFCLASS64)) {
+		return;  /* Wrong ELF class -- check ELF_BITS */
+	}
+
+	ELF(Phdr) *pt = (ELF(Phdr)*)(vdso_info.load_addr + hdr->e_phoff);
+	ELF(Dyn) *dyn = 0;
+
+	/*
+	 * We need two things from the segment table: the load offset
+	 * and the dynamic table.
+	 */
+	for (i = 0; i < hdr->e_phnum; i++)
+	{
+		if (pt[i].p_type == PT_LOAD && !found_vaddr) {
+			found_vaddr = true;
+			vdso_info.load_offset =	base
+				+ (uintptr_t)pt[i].p_offset
+				- (uintptr_t)pt[i].p_vaddr;
+		} else if (pt[i].p_type == PT_DYNAMIC) {
+			dyn = (ELF(Dyn)*)(base + pt[i].p_offset);
+		}
+	}
+
+	if (!found_vaddr || !dyn)
+		return;  /* Failed */
+
+	/*
+	 * Fish out the useful bits of the dynamic table.
+	 */
+	ELF_HASH_ENTRY *hash = 0;
+	vdso_info.symstrings = 0;
+	vdso_info.gnu_hash = 0;
+	vdso_info.symtab = 0;
+	vdso_info.versym = 0;
+	vdso_info.verdef = 0;
+	for (i = 0; dyn[i].d_tag != DT_NULL; i++) {
+		switch (dyn[i].d_tag) {
+		case DT_STRTAB:
+			vdso_info.symstrings = (const char *)
+				((uintptr_t)dyn[i].d_un.d_ptr
+				 + vdso_info.load_offset);
+			break;
+		case DT_SYMTAB:
+			vdso_info.symtab = (ELF(Sym) *)
+				((uintptr_t)dyn[i].d_un.d_ptr
+				 + vdso_info.load_offset);
+			break;
+		case DT_HASH:
+			hash = (ELF_HASH_ENTRY *)
+				((uintptr_t)dyn[i].d_un.d_ptr
+				 + vdso_info.load_offset);
+			break;
+		case DT_GNU_HASH:
+			vdso_info.gnu_hash =
+				(ELF(Word) *)((uintptr_t)dyn[i].d_un.d_ptr +
+					      vdso_info.load_offset);
+			break;
+		case DT_VERSYM:
+			vdso_info.versym = (ELF(Versym) *)
+				((uintptr_t)dyn[i].d_un.d_ptr
+				 + vdso_info.load_offset);
+			break;
+		case DT_VERDEF:
+			vdso_info.verdef = (ELF(Verdef) *)
+				((uintptr_t)dyn[i].d_un.d_ptr
+				 + vdso_info.load_offset);
+			break;
+		}
+	}
+	if (!vdso_info.symstrings || !vdso_info.symtab ||
+	    (!hash && !vdso_info.gnu_hash))
+		return;  /* Failed */
+
+	if (!vdso_info.verdef)
+		vdso_info.versym = 0;
+
+	/* Parse the hash table header. */
+	if (vdso_info.gnu_hash) {
+		vdso_info.nbucket = vdso_info.gnu_hash[0];
+		/* The bucket array is located after the header (4 uint32) and the bloom
+		 * filter (size_t array of gnu_hash[2] elements).
+		 */
+		vdso_info.gnu_bucket = vdso_info.gnu_hash + 4 +
+				       sizeof(size_t) / 4 * vdso_info.gnu_hash[2];
+	} else {
+		vdso_info.nbucket = hash[0];
+		vdso_info.nchain = hash[1];
+		vdso_info.bucket = &hash[2];
+		vdso_info.chain = &hash[vdso_info.nbucket + 2];
+	}
+
+	/* That's all we need. */
+	vdso_info.valid = true;
+}
+
+static bool vdso_match_version(ELF(Versym) ver,
+			       const char *name, ELF(Word) hash)
+{
+	/*
+	 * This is a helper function to check if the version indexed by
+	 * ver matches name (which hashes to hash).
+	 *
+	 * The version definition table is a mess, and I don't know how
+	 * to do this in better than linear time without allocating memory
+	 * to build an index.  I also don't know why the table has
+	 * variable size entries in the first place.
+	 *
+	 * For added fun, I can't find a comprehensible specification of how
+	 * to parse all the weird flags in the table.
+	 *
+	 * So I just parse the whole table every time.
+	 */
+
+	/* First step: find the version definition */
+	ver &= 0x7fff;  /* Apparently bit 15 means "hidden" */
+	ELF(Verdef) *def = vdso_info.verdef;
+	while(true) {
+		if ((def->vd_flags & VER_FLG_BASE) == 0
+		    && (def->vd_ndx & 0x7fff) == ver)
+			break;
+
+		if (def->vd_next == 0)
+			return false;  /* No definition. */
+
+		def = (ELF(Verdef) *)((char *)def + def->vd_next);
+	}
+
+	/* Now figure out whether it matches. */
+	ELF(Verdaux) *aux = (ELF(Verdaux)*)((char *)def + def->vd_aux);
+	return def->vd_hash == hash
+		&& !strcmp(name, vdso_info.symstrings + aux->vda_name);
+}
+
+static bool check_sym(ELF(Sym) *sym, ELF(Word) i, const char *name,
+		      const char *version, unsigned long ver_hash)
+{
+	/* Check for a defined global or weak function w/ right name. */
+	if (ELF64_ST_TYPE(sym->st_info) != STT_FUNC)
+		return false;
+	if (ELF64_ST_BIND(sym->st_info) != STB_GLOBAL &&
+	    ELF64_ST_BIND(sym->st_info) != STB_WEAK)
+		return false;
+	if (strcmp(name, vdso_info.symstrings + sym->st_name))
+		return false;
+
+	/* Check symbol version. */
+	if (vdso_info.versym &&
+	    !vdso_match_version(vdso_info.versym[i], version, ver_hash))
+		return false;
+
+	return true;
+}
+
+void *vdso_sym(const char *version, const char *name)
+{
+	unsigned long ver_hash;
+	if (!vdso_info.valid)
+		return 0;
+
+	ver_hash = elf_hash(version);
+	ELF(Word) i;
+
+	if (vdso_info.gnu_hash) {
+		uint32_t h1 = gnu_hash(name), h2, *hashval;
+
+		i = vdso_info.gnu_bucket[h1 % vdso_info.nbucket];
+		if (i == 0)
+			return 0;
+		h1 |= 1;
+		hashval = vdso_info.gnu_bucket + vdso_info.nbucket +
+			  (i - vdso_info.gnu_hash[1]);
+		for (;; i++) {
+			ELF(Sym) *sym = &vdso_info.symtab[i];
+			h2 = *hashval++;
+			if (h1 == (h2 | 1) &&
+			    check_sym(sym, i, name, version, ver_hash))
+				return (void *)(vdso_info.load_offset +
+						sym->st_value);
+			if (h2 & 1)
+				break;
+		}
+	} else {
+		i = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];
+		for (; i; i = vdso_info.chain[i]) {
+			ELF(Sym) *sym = &vdso_info.symtab[i];
+			if (sym->st_shndx != SHN_UNDEF &&
+			    check_sym(sym, i, name, version, ver_hash))
+				return (void *)(vdso_info.load_offset +
+						sym->st_value);
+		}
+	}
+
+	return 0;
+}