Commit e0746bde authored by Fangrui Song's avatar Fangrui Song Committed by Shuah Khan
Browse files

selftests/vDSO: support DT_GNU_HASH 

glibc added support for DT_GNU_HASH in 2006 and DT_HASH has been
obsoleted for more than one decade in many Linux distributions.

Many vDSOs support DT_GNU_HASH. This patch adds selftests support.

Link: https://lore.kernel.org/r/20241206130724.7944-2-xry111@xry111.site


Signed-off-by: default avatarFangrui Song <i@maskray.me>
Tested-by: default avatarXi Ruoyao <xry111@xry111.site>
Signed-off-by: Xi Ruoyao <xry111@xry111.site> # rebase
Signed-off-by: default avatarShuah Khan <skhan@linuxfoundation.org>
parent eed8ecdf

tools/testing/selftests/vDSO/parse_vdso.c

+82 −28
Original line number Diff line number Diff line
@@ -53,6 +53,7 @@ static struct vdso_info 
	/* Symbol table */

	ELF(Sym) *symtab;

	const char *symstrings;

	ELF(Word) *gnu_hash;

	ELF_HASH_ENTRY *bucket, *chain;

	ELF_HASH_ENTRY nbucket, nchain;
@@ -81,6 +82,16 @@ static unsigned long elf_hash(const char *name) 
	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;
@@ -123,6 +134,7 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base) 
	 */

	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;
@@ -143,6 +155,11 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base) 
				((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
@@ -155,17 +172,27 @@ void vdso_init_from_sysinfo_ehdr(uintptr_t base) 
			break;

		}

	}

	if (!vdso_info.symstrings || !vdso_info.symtab || !hash)

	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.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;
@@ -209,36 +236,63 @@ static bool vdso_match_version(ELF(Versym) ver, 
		&& !strcmp(name, vdso_info.symstrings + aux->vda_name);

}



void *vdso_sym(const char *version, const char *name)

static bool check_sym(ELF(Sym) *sym, ELF(Word) i, const char *name,

		      const char *version, unsigned long ver_hash)

{

	unsigned long ver_hash;

	if (!vdso_info.valid)

		return 0;



	ver_hash = elf_hash(version);

	ELF(Word) chain = vdso_info.bucket[elf_hash(name) % vdso_info.nbucket];



	for (; chain != STN_UNDEF; chain = vdso_info.chain[chain]) {

		ELF(Sym) *sym = &vdso_info.symtab[chain];



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

	if (ELF64_ST_TYPE(sym->st_info) != STT_FUNC)

			continue;

		return false;

	if (ELF64_ST_BIND(sym->st_info) != STB_GLOBAL &&

	    ELF64_ST_BIND(sym->st_info) != STB_WEAK)

			continue;

		if (sym->st_shndx == SHN_UNDEF)

			continue;

		return false;

	if (strcmp(name, vdso_info.symstrings + sym->st_name))

			continue;

		return false;



	/* Check symbol version. */

		if (vdso_info.versym

		    && !vdso_match_version(vdso_info.versym[chain],

					   version, ver_hash))

			continue;

	if (vdso_info.versym &&

	    !vdso_match_version(vdso_info.versym[i], version, ver_hash))

		return false;



		return (void *)(vdso_info.load_offset + sym->st_value);

	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.bucket[h1 % vdso_info.nbucket];

		if (i == 0)

			return 0;

		h1 |= 1;

		hashval = vdso_info.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;