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Prepare the kernel linker to handle PC-relative ifunc relocations.

Browse Source 
The boot-time ifunc resolver assumes that it only needs to apply
IRELATIVE relocations to PLT entries.  With an upcoming optimization,
this assumption no longer holds, so add the support required to handle
PC-relative relocations targeting GNU_IFUNC symbols.
- Provide a custom symbol lookup routine that can be used in early boot.
  The default lookup routine uses kobj, which is not functional at that
  point.
- Apply all existing relocations during boot rather than filtering
  IRELATIVE relocations.
- Ensure that we continue to apply ifunc relocations in a second pass
  when loading a kernel module.

Reviewed by:	kib
MFC after:	1 month
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D16749
This commit is contained in:
Mark Johnston 2018-08-22 20:44:30 +00:00
parent 657d21589e
commit 36716fe2e6
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=338211
12 changed files with 140 additions and 128 deletions
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27
sys/amd64/amd64/elf_machdep.c
View File

@ -175,13 +175,17 @@ elf64_dump_thread(struct thread *td, void *dst, size_t *off)
*off = len;
}
#define ERI_LOCAL 0x0001
#define ERI_ONLYIFUNC 0x0002
bool
elf_is_ifunc_reloc(Elf_Size r_info)
{
return (ELF_R_TYPE(r_info) == R_X86_64_IRELATIVE);
}
/* Process one elf relocation with addend. */
static int
elf_reloc_internal(linker_file_t lf, Elf_Addr relocbase, const void *data,
int type, elf_lookup_fn lookup, int flags)
int type, elf_lookup_fn lookup)
{
Elf64_Addr *where, val;
Elf32_Addr *where32, val32;
@ -221,9 +225,6 @@ elf_reloc_internal(linker_file_t lf, Elf_Addr relocbase, const void *data,
panic("unknown reloc type %d\n", type);
}
if (((flags & ERI_ONLYIFUNC) == 0) ^ (rtype != R_X86_64_IRELATIVE))
return (0);
switch (rtype) {
case R_X86_64_NONE: /* none */
break;
@ -299,21 +300,12 @@ elf_reloc_internal(linker_file_t lf, Elf_Addr relocbase, const void *data,
return (0);
}
int
elf_reloc_ifunc(linker_file_t lf, Elf_Addr relocbase, const void *data,
int type, elf_lookup_fn lookup)
{
return (elf_reloc_internal(lf, relocbase, data, type, lookup,
ERI_ONLYIFUNC));
}
int
elf_reloc(linker_file_t lf, Elf_Addr relocbase, const void *data, int type,
elf_lookup_fn lookup)
{
return (elf_reloc_internal(lf, relocbase, data, type, lookup, 0));
return (elf_reloc_internal(lf, relocbase, data, type, lookup));
}
int
@ -321,8 +313,7 @@ elf_reloc_local(linker_file_t lf, Elf_Addr relocbase, const void *data,
int type, elf_lookup_fn lookup)
{
return (elf_reloc_internal(lf, relocbase, data, type, lookup,
ERI_LOCAL));
return (elf_reloc_internal(lf, relocbase, data, type, lookup));
}
int

7
sys/arm/arm/elf_machdep.c
View File

@ -149,6 +149,13 @@ elf32_dump_thread(struct thread *td, void *dst, size_t *off)
#endif
}
bool
elf_is_ifunc_reloc(Elf_Size r_info __unused)
{
return (false);
}
/*
* It is possible for the compiler to emit relocations for unaligned data.
* We handle this situation with these inlines.

7
sys/arm64/arm64/elf_machdep.c
View File

@ -129,6 +129,13 @@ elf64_dump_thread(struct thread *td __unused, void *dst __unused,
}
bool
elf_is_ifunc_reloc(Elf_Size r_info __unused)
{
return (false);
}
static int
elf_reloc_internal(linker_file_t lf, Elf_Addr relocbase, const void *data,
int type, int local, elf_lookup_fn lookup)

20
sys/i386/i386/elf_machdep.c
View File

@ -159,8 +159,14 @@ elf32_dump_thread(struct thread *td, void *dst, size_t *off)
*off = len;
}
bool
elf_is_ifunc_reloc(Elf_Size r_info)
{
return (ELF_R_TYPE(r_info) == R_386_IRELATIVE);
}
#define ERI_LOCAL 0x0001
#define ERI_ONLYIFUNC 0x0002
/* Process one elf relocation with addend. */
static int
@ -194,9 +200,6 @@ elf_reloc_internal(linker_file_t lf, Elf_Addr relocbase, const void *data,
panic("unknown reloc type %d\n", type);
}
if (((flags & ERI_ONLYIFUNC) == 0) ^ (rtype != R_386_IRELATIVE))
return (0);
if ((flags & ERI_LOCAL) != 0) {
if (rtype == R_386_RELATIVE) { /* A + B */
addr = elf_relocaddr(lf, relocbase + addend);
@ -263,15 +266,6 @@ elf_reloc_internal(linker_file_t lf, Elf_Addr relocbase, const void *data,
return(0);
}
int
elf_reloc_ifunc(linker_file_t lf, Elf_Addr relocbase, const void *data,
int type, elf_lookup_fn lookup)
{
return (elf_reloc_internal(lf, relocbase, data, type, lookup,
ERI_ONLYIFUNC));
}
int
elf_reloc(linker_file_t lf, Elf_Addr relocbase, const void *data, int type,
elf_lookup_fn lookup)

152
sys/kern/link_elf.c
View File

@ -188,11 +188,13 @@ static struct linker_class link_elf_class = {
link_elf_methods, sizeof(struct elf_file)
};
typedef int (*elf_reloc_fn)(linker_file_t lf, Elf_Addr relocbase,
const void *data, int type, elf_lookup_fn lookup);
static int parse_dynamic(elf_file_t);
static int relocate_file(elf_file_t);
static int relocate_file1(elf_file_t ef, int (*elf_reloc_func)(
linker_file_t lf, Elf_Addr relocbase, const void *data,
int type, elf_lookup_fn lookup));
static int relocate_file1(elf_file_t ef, elf_lookup_fn lookup,
elf_reloc_fn reloc, bool ifuncs);
static int link_elf_preload_parse_symbols(elf_file_t);
static struct elf_set_head set_pcpu_list;
@ -1185,81 +1187,48 @@ symbol_name(elf_file_t ef, Elf_Size r_info)
}
static int
relocate_file1(elf_file_t ef, int (*elf_reloc_func)(linker_file_t lf,
Elf_Addr relocbase, const void *data, int type, elf_lookup_fn lookup))
symbol_type(elf_file_t ef, Elf_Size r_info)
{
const Elf_Sym *ref;
if (ELF_R_SYM(r_info)) {
ref = ef->symtab + ELF_R_SYM(r_info);
return (ELF_ST_TYPE(ref->st_info));
}
return (STT_NOTYPE);
}
static int
relocate_file1(elf_file_t ef, elf_lookup_fn lookup, elf_reloc_fn reloc,
bool ifuncs)
{
const Elf_Rel *rellim;
const Elf_Rel *rel;
const Elf_Rela *relalim;
const Elf_Rela *rela;
const char *symname;
/* Perform relocations without addend if there are any: */
rel = ef->rel;
if (rel != NULL) {
rellim = (const Elf_Rel *)
((const char *)ef->rel + ef->relsize);
while (rel < rellim) {
if (elf_reloc_func(&ef->lf, (Elf_Addr)ef->address, rel,
ELF_RELOC_REL, elf_lookup)) {
symname = symbol_name(ef, rel->r_info);
printf("link_elf: symbol %s undefined\n", symname);
return (ENOENT);
}
rel++;
}
}
#define APPLY_RELOCS(iter, tbl, tblsize, type) do { \
for ((iter) = (tbl); (iter) != NULL && \
(iter) < (tbl) + (tblsize) / sizeof(*(iter)); (iter)++) { \
if ((symbol_type(ef, (iter)->r_info) == \
STT_GNU_IFUNC || \
elf_is_ifunc_reloc((iter)->r_info)) != ifuncs) \
continue; \
if (reloc(&ef->lf, (Elf_Addr)ef->address, \
(iter), (type), lookup)) { \
symname = symbol_name(ef, (iter)->r_info); \
printf("link_elf: symbol %s undefined\n", \
symname); \
return (ENOENT); \
} \
} \
} while (0)
/* Perform relocations with addend if there are any: */
rela = ef->rela;
if (rela != NULL) {
relalim = (const Elf_Rela *)
((const char *)ef->rela + ef->relasize);
while (rela < relalim) {
if (elf_reloc_func(&ef->lf, (Elf_Addr)ef->address, rela,
ELF_RELOC_RELA, elf_lookup)) {
symname = symbol_name(ef, rela->r_info);
printf("link_elf: symbol %s undefined\n",
symname);
return (ENOENT);
}
rela++;
}
}
APPLY_RELOCS(rel, ef->rel, ef->relsize, ELF_RELOC_REL);
APPLY_RELOCS(rela, ef->rela, ef->relasize, ELF_RELOC_RELA);
APPLY_RELOCS(rel, ef->pltrel, ef->pltrelsize, ELF_RELOC_REL);
APPLY_RELOCS(rela, ef->pltrela, ef->pltrelasize, ELF_RELOC_RELA);
/* Perform PLT relocations without addend if there are any: */
rel = ef->pltrel;
if (rel != NULL) {
rellim = (const Elf_Rel *)
((const char *)ef->pltrel + ef->pltrelsize);
while (rel < rellim) {
if (elf_reloc_func(&ef->lf, (Elf_Addr)ef->address, rel,
ELF_RELOC_REL, elf_lookup)) {
symname = symbol_name(ef, rel->r_info);
printf("link_elf: symbol %s undefined\n",
symname);
return (ENOENT);
}
rel++;
}
}
/* Perform relocations with addend if there are any: */
rela = ef->pltrela;
if (rela != NULL) {
relalim = (const Elf_Rela *)
((const char *)ef->pltrela + ef->pltrelasize);
while (rela < relalim) {
if (elf_reloc_func(&ef->lf, (Elf_Addr)ef->address, rela,
ELF_RELOC_RELA, elf_lookup)) {
symname = symbol_name(ef, rela->r_info);
printf("link_elf: symbol %s undefined\n",
symname);
return (ENOENT);
}
rela++;
}
}
#undef APPLY_RELOCS
return (0);
}
@ -1267,14 +1236,12 @@ relocate_file1(elf_file_t ef, int (*elf_reloc_func)(linker_file_t lf,
static int
relocate_file(elf_file_t ef)
{
int e;
int error;
e = relocate_file1(ef, elf_reloc);
#if defined(__i386__) || defined(__amd64__)
if (e == 0)
e = relocate_file1(ef, elf_reloc_ifunc);
#endif
return (e);
error = relocate_file1(ef, elf_lookup, elf_reloc, false);
if (error == 0)
error = relocate_file1(ef, elf_lookup, elf_reloc, true);
return (error);
}
/*
@ -1298,7 +1265,7 @@ elf_hash(const char *name)
}
static int
link_elf_lookup_symbol(linker_file_t lf, const char* name, c_linker_sym_t* sym)
link_elf_lookup_symbol(linker_file_t lf, const char *name, c_linker_sym_t *sym)
{
elf_file_t ef = (elf_file_t) lf;
unsigned long symnum;
@ -1687,6 +1654,29 @@ link_elf_strtab_get(linker_file_t lf, caddr_t *strtab)
}
#if defined(__i386__) || defined(__amd64__)
/*
* Use this lookup routine when performing relocations early during boot.
* The generic lookup routine depends on kobj, which is not initialized
* at that point.
*/
static int
elf_lookup_ifunc(linker_file_t lf, Elf_Size symidx, int deps __unused,
Elf_Addr *res)
{
elf_file_t ef;
const Elf_Sym *symp;
caddr_t val;
ef = (elf_file_t)lf;
symp = ef->symtab + symidx;
if (ELF_ST_TYPE(symp->st_info) == STT_GNU_IFUNC) {
val = (caddr_t)ef->address + symp->st_value;
*res = ((Elf_Addr (*)(void))val)();
return (0);
}
return (ENOENT);
}
void
link_elf_ireloc(caddr_t kmdp)
{
@ -1695,7 +1685,7 @@ link_elf_ireloc(caddr_t kmdp)
volatile char *c;
size_t i;
ef = &eff;
ef = &eff;
/* Do not use bzero/memset before ireloc is done. */
for (c = (char *)ef, i = 0; i < sizeof(*ef); i++)
@ -1706,6 +1696,6 @@ link_elf_ireloc(caddr_t kmdp)
parse_dynamic(ef);
ef->address = 0;
link_elf_preload_parse_symbols(ef);
relocate_file1(ef, elf_reloc_ifunc);
relocate_file1(ef, elf_lookup_ifunc, elf_reloc, true);
}
#endif

18
sys/kern/link_elf_obj.c
View File

@ -1521,15 +1521,10 @@ link_elf_reloc_local(linker_file_t lf, bool ifuncs)
/* Only do local relocs */
if (ELF_ST_BIND(sym->st_info) != STB_LOCAL)
continue;
if ((ELF_ST_TYPE(sym->st_info) == STT_GNU_IFUNC) ==
ifuncs)
if ((ELF_ST_TYPE(sym->st_info) == STT_GNU_IFUNC ||
elf_is_ifunc_reloc(rel->r_info)) == ifuncs)
elf_reloc_local(lf, base, rel, ELF_RELOC_REL,
elf_obj_lookup);
#if defined(__i386__) || defined(__amd64__)
else if (ifuncs)
elf_reloc_ifunc(lf, base, rel, ELF_RELOC_REL,
elf_obj_lookup);
#endif
}
}
@ -1554,15 +1549,10 @@ link_elf_reloc_local(linker_file_t lf, bool ifuncs)
/* Only do local relocs */
if (ELF_ST_BIND(sym->st_info) != STB_LOCAL)
continue;
if ((ELF_ST_TYPE(sym->st_info) == STT_GNU_IFUNC) ==
ifuncs)
if ((ELF_ST_TYPE(sym->st_info) == STT_GNU_IFUNC ||
elf_is_ifunc_reloc(rela->r_info)) == ifuncs)
elf_reloc_local(lf, base, rela, ELF_RELOC_RELA,
elf_obj_lookup);
#if defined(__i386__) || defined(__amd64__)
else if (ifuncs)
elf_reloc_ifunc(lf, base, rela, ELF_RELOC_RELA,
elf_obj_lookup);
#endif
}
}
return (0);

7
sys/mips/mips/elf_machdep.c
View File

@ -295,6 +295,13 @@ mips_tmp_reloc_free(struct mips_tmp_reloc *r)
free(r, M_TEMP);
}
bool
elf_is_ifunc_reloc(Elf_Size r_info __unused)
{
return (false);
}
/* Process one elf relocation with addend. */
static int
elf_reloc_internal(linker_file_t lf, Elf_Addr relocbase, const void *data,

7
sys/powerpc/powerpc/elf32_machdep.c
View File

@ -214,6 +214,13 @@ elf32_dump_thread(struct thread *td, void *dst, size_t *off)
}
#ifndef __powerpc64__
bool
elf_is_ifunc_reloc(Elf_Size r_info __unused)
{
return (false);
}
/* Process one elf relocation with addend. */
static int
elf_reloc_internal(linker_file_t lf, Elf_Addr relocbase, const void *data,

6
sys/powerpc/powerpc/elf64_machdep.c
View File

@ -276,6 +276,12 @@ elf64_dump_thread(struct thread *td, void *dst, size_t *off)
*off = len;
}
bool
elf_is_ifunc_reloc(Elf_Size r_info __unused)
{
return (false);
}
/* Process one elf relocation with addend. */
static int

7
sys/riscv/riscv/elf_machdep.c
View File

@ -259,6 +259,13 @@ reloctype_to_str(int type)
return "*unknown*";
}
bool
elf_is_ifunc_reloc(Elf_Size r_info __unused)
{
return (false);
}
/*
* Currently kernel loadable module for RISCV is compiled with -fPIC option.
* (see also additional CFLAGS definition for RISCV in sys/conf/kmod.mk)

7
sys/sparc64/sparc64/elf_machdep.c
View File

@ -312,6 +312,13 @@ static const long reloc_target_bitmask[] = {
};
#define RELOC_VALUE_BITMASK(t) (reloc_target_bitmask[t])
bool
elf_is_ifunc_reloc(Elf_Size r_info __unused)
{
return (false);
}
int
elf_reloc_local(linker_file_t lf, Elf_Addr relocbase, const void *data,
int type, elf_lookup_fn lookup __unused)

3
sys/sys/linker.h
View File

@ -272,10 +272,9 @@ extern int kld_debug;
typedef int elf_lookup_fn(linker_file_t, Elf_Size, int, Elf_Addr *);
/* Support functions */
bool elf_is_ifunc_reloc(Elf_Size r_info);
int elf_reloc(linker_file_t _lf, Elf_Addr base, const void *_rel,
int _type, elf_lookup_fn _lu);
int elf_reloc_ifunc(linker_file_t _lf, Elf_Addr base, const void *_rel,
int _type, elf_lookup_fn _lu);
int elf_reloc_local(linker_file_t _lf, Elf_Addr base, const void *_rel,
int _type, elf_lookup_fn _lu);
Elf_Addr elf_relocaddr(linker_file_t _lf, Elf_Addr addr);