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c18n: Save metadata in trampoline headers
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Trampoline metadata is no longer stored in a separate array. This
permits runtime introspection of trampoline metadata.
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@dpgao
dpgao committed Mar 7, 2024
1 parent 2f83ff4 commit cfef181
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Showing 3 changed files with 95 additions and 97 deletions.
49 changes: 21 additions & 28 deletions libexec/rtld-elf/aarch64/rtld_c18n_machdep.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -42,22 +42,12 @@
* Trampolines
*/
size_t
tramp_compile(void **entry, const struct tramp_data *data)
tramp_compile(struct tramp_header **entry, const struct tramp_data *data)
{
#define IMPORT(template) \
extern const uint32_t tramp_##template[]; \
extern const size_t size_tramp_##template

struct {
void *target;
} header;

struct {
const Obj_Entry *defobj;
const Elf_Sym *def;
void *function;
} header_hook;

IMPORT(save_caller);
IMPORT(call_hook);
IMPORT(switch_stack);
Expand All @@ -72,7 +62,15 @@ tramp_compile(void **entry, const struct tramp_data *data)

#undef IMPORT

uint32_t *buf = *entry;
void *header_hook = tramp_hook;

struct tramp_header header = {
.target = data->target,
.defobj = data->defobj,
.def = data->def
};

void *buf = *entry;
uint32_t *cookie_patch;
size_t size = 0;
int to_clear;
Expand All @@ -95,7 +93,8 @@ tramp_compile(void **entry, const struct tramp_data *data)

#define PATCH_POINT(tramp, name) ({ \
extern const int32_t patch_tramp_##tramp##_##name; \
&buf[patch_tramp_##tramp##_##name / sizeof(*buf)]; \
&((uint32_t *)buf) \
[patch_tramp_##tramp##_##name / sizeof(uint32_t)]; \
})

#define PATCH_MOV(tramp, name, value) \
Expand Down Expand Up @@ -131,30 +130,24 @@ tramp_compile(void **entry, const struct tramp_data *data)
*(point) |= _offset; \
} while (0)

header.target = data->target;
COPY_DATA(header);

if (hook) {
header_hook.defobj = data->defobj;
header_hook.def = data->def;
header_hook.function = tramp_hook;
if (hook)
COPY_DATA(header_hook);
}

*entry = buf;
COPY_DATA(header);

COPY(save_caller);
cookie_patch = PATCH_POINT(save_caller, cookie);
PATCH_LDR_IMM(save_caller, target, 0);
PATCH_LDR_IMM(save_caller, target, hook ? 1 : 0);
if (data->sig.valid)
PATCH_ADD(save_caller, ret_args, data->sig.ret_args);

if (hook) {
COPY(call_hook);
PATCH_MOV(call_hook, event, UTRACE_COMPARTMENT_ENTER);
PATCH_LDR_IMM(call_hook, obj, 1);
PATCH_LDR_IMM(call_hook, def, 2);
PATCH_LDR_IMM(call_hook, function, 3);
PATCH_LDR_IMM(call_hook, function, 0);
PATCH_LDR_IMM(call_hook, obj, 2);
PATCH_LDR_IMM(call_hook, def, 3);
}

#ifdef __ARM_MORELLO_PURECAP_BENCHMARK_ABI
Expand Down Expand Up @@ -192,9 +185,9 @@ tramp_compile(void **entry, const struct tramp_data *data)
if (hook) {
COPY(return_hook);
PATCH_MOV(return_hook, event, UTRACE_COMPARTMENT_LEAVE);
PATCH_LDR_IMM(return_hook, obj, 1);
PATCH_LDR_IMM(return_hook, def, 2);
PATCH_LDR_IMM(return_hook, function, 3);
PATCH_LDR_IMM(return_hook, function, 0);
PATCH_LDR_IMM(return_hook, obj, 2);
PATCH_LDR_IMM(return_hook, def, 3);
} else
COPY(return);

Expand Down
129 changes: 64 additions & 65 deletions libexec/rtld-elf/rtld_c18n.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -613,19 +613,14 @@ tramp_pg_push(struct tramp_pg *pg, size_t len)
size_t size = atomic_load_explicit(&pg->size, memory_order_relaxed);

do {
/*
* Align the trampoline to two capabilities so that the first
* instruction and the capability preceding it reside on the
* same cache line.
*/
tramp = roundup2(pg->trampolines + size, 2 * _Alignof(void *));
tramp = roundup2(pg->trampolines + size,
_Alignof(struct tramp_header));
n_size = tramp + len - pg->trampolines;
if (n_size > pg->capacity)
return (NULL);
} while (!atomic_compare_exchange_weak_explicit(&pg->size,
/*
* Relaxed ordering is sufficient because there are no
* side-effects.
* Relaxed ordering is sufficient because there are no side-effects.
*/
&size, n_size, memory_order_relaxed, memory_order_relaxed));

Expand All @@ -641,7 +636,7 @@ static struct {
_Alignas(CACHE_LINE_SIZE) _Atomic(slot_idx_t) size;
size_t back;
int exp;
struct tramp_data *data;
struct tramp_header **data;
struct tramp_map_kv {
_Atomic(ptraddr_t) key;
_Atomic(slot_idx_t) index;
Expand Down Expand Up @@ -738,7 +733,7 @@ resize_table(int exp)
size = atomic_load_explicit(&tramp_table.size, memory_order_relaxed);

for (slot_idx_t idx = 0; idx < size; ++idx) {
key = (ptraddr_t)tramp_table.data[idx].target;
key = (ptraddr_t)tramp_table.data[idx]->target;
hash = pointer_hash(key);
slot = hash;

Expand Down Expand Up @@ -807,19 +802,22 @@ tramp_hook_impl(void *rcsp, int event, void *target, const Obj_Entry *obj,
getpid();
}

#define C18N_MAX_TRAMPOLINE_SIZE 768
#define C18N_MAX_TRAMP_SIZE 768

static void *
static struct tramp_header *
tramp_pgs_append(const struct tramp_data *data)
{
size_t len;
/* A capability-aligned buffer large enough to hold a trampoline */
_Alignas(_Alignof(void *)) char tmp[C18N_MAX_TRAMPOLINE_SIZE];
char *tramp, *entry = tmp;
_Alignas(_Alignof(struct tramp_header)) char buf[C18N_MAX_TRAMP_SIZE];
char *bufp = buf;
struct tramp_header **headerp = (struct tramp_header **)&bufp;

char *tramp;
struct tramp_pg *pg;

/* Fill a temporary buffer with the trampoline and obtain its length */
len = tramp_compile((void **)&entry, data);
len = tramp_compile(headerp, data);

pg = atomic_load_explicit(&tramp_pgs.head, memory_order_acquire);
tramp = tramp_pg_push(pg, len);
Expand All @@ -840,23 +838,18 @@ tramp_pgs_append(const struct tramp_data *data)
}
assert(cheri_gettag(tramp));

entry = tramp + (entry - tmp);
memcpy(tramp, tmp, len);
bufp = tramp + (bufp - buf);
memcpy(tramp, buf, len);

/*
* Ensure i- and d-cache coherency after writing executable code. The
* __clear_cache procedure rounds the addresses to cache-line-aligned
* addresses. Derive the start/end addresses from pg so that they have
* addresses. Derive the start address from pg so that it has
* sufficiently large bounds to contain these rounded addresses.
*/
__clear_cache(cheri_copyaddress(pg, entry),
cheri_copyaddress(pg, tramp + len));
__clear_cache(cheri_copyaddress(pg, (*headerp)->entry), tramp + len);

entry = cheri_clearperm(entry, FUNC_PTR_REMOVE_PERMS);
#ifndef __ARM_MORELLO_PURECAP_BENCHMARK_ABI
entry = cheri_capmode(entry);
#endif
return (cheri_sealentry(entry));
return (*headerp);
}

static bool
Expand All @@ -867,55 +860,55 @@ func_sig_equal(struct func_sig lhs, struct func_sig rhs)
lhs.ret_args == rhs.ret_args);
}

static bool
func_sig_compatible(struct func_sig lhs, struct func_sig rhs)
static void
tramp_check_sig(struct tramp_header *found, const Obj_Entry *reqobj,
const struct tramp_data *data)
{
return (!lhs.valid || !rhs.valid || func_sig_equal(lhs, rhs));
struct func_sig sig;

if (data->sig.valid && found->def != NULL) {
sig = sigtab_get(found->defobj,
found->def - found->defobj->symtab);

rtld_require(!sig.valid || func_sig_equal(data->sig, sig),
"Incompatible signatures for function %s: "
"%s requests " C18N_SIG_FORMAT_STRING " but "
"%s provides " C18N_SIG_FORMAT_STRING,
strtab_value(found->defobj, found->def->st_name),
reqobj->path, C18N_SIG_FORMAT(data->sig),
found->defobj->path, C18N_SIG_FORMAT(sig));
}
}

static void *
tramp_get_entry(const struct tramp_data *found, const struct tramp_data *data)
static struct tramp_header *
tramp_create(const struct tramp_data *data)
{
if (!func_sig_compatible(found->sig, data->sig))
rtld_fatal(
"Incompatible signatures for function %s: "
"%s requests " C18N_SIG_FORMAT_STRING " but %s provides "
C18N_SIG_FORMAT_STRING,
strtab_value(data->defobj, data->def->st_name),
data->defobj->path, C18N_SIG_FORMAT(data->sig),
found->defobj->path, C18N_SIG_FORMAT(found->sig));
struct tramp_data newdata = *data;

return (found->entry);
if (!newdata.sig.valid && newdata.def != NULL)
newdata.sig = sigtab_get(newdata.defobj,
newdata.def - newdata.defobj->symtab);

return (tramp_pgs_append(&newdata));
}

static void *
tramp_create_entry(struct tramp_data *found, const struct tramp_data *data)
tramp_make_entry(struct tramp_header *header)
{
struct func_sig sig;
void *entry = header->entry;

*found = *data;
if (found->def != NULL) {
sig = sigtab_get(found->defobj,
found->def - found->defobj->symtab);
if (!found->sig.valid)
found->sig = sig;
else if (!func_sig_compatible(found->sig, sig))
rtld_fatal(
"Incompatible signatures for function %s: "
"requests " C18N_SIG_FORMAT_STRING
" but %s provides " C18N_SIG_FORMAT_STRING,
strtab_value(found->defobj, found->def->st_name),
C18N_SIG_FORMAT(found->sig), found->defobj->path,
C18N_SIG_FORMAT(sig));
}
entry = cheri_clearperm(entry, FUNC_PTR_REMOVE_PERMS);
#ifndef __ARM_MORELLO_PURECAP_BENCHMARK_ABI
entry = cheri_capmode(entry);
#endif

return (found->entry = tramp_pgs_append(found));
return (cheri_sealentry(entry));
}

void *
tramp_intern(const Obj_Entry *reqobj, const struct tramp_data *data)
{
void *entry;
struct tramp_header *header;
RtldLockState lockstate;
ptraddr_t target = (ptraddr_t)data->target;
const uint32_t hash = pointer_hash(target);
Expand All @@ -924,9 +917,8 @@ tramp_intern(const Obj_Entry *reqobj, const struct tramp_data *data)
int exp;

/* reqobj == NULL iff the request is by RTLD */
assert((reqobj == NULL || data->def != NULL) &&
data->defobj != NULL && data->entry == NULL &&
func_sig_legal(data->sig));
assert((reqobj == NULL || data->def != NULL) && data->defobj != NULL
&& func_sig_legal(data->sig));

if (!tramp_should_include(reqobj, data))
return (data->target);
Expand Down Expand Up @@ -986,7 +978,10 @@ tramp_intern(const Obj_Entry *reqobj, const struct tramp_data *data)
memory_order_acquire);
while (idx == -1);

entry = tramp_get_entry(&tramp_table.data[idx], data);
/*
* Load the data array entry and exit the critical region.
*/
header = tramp_table.data[idx];
goto end;

insert:
Expand All @@ -998,7 +993,7 @@ tramp_intern(const Obj_Entry *reqobj, const struct tramp_data *data)
*
* Create the data array entry.
*/
entry = tramp_create_entry(&tramp_table.data[idx], data);
header = tramp_table.data[idx] = tramp_create(data);

/*
* Store-release the index.
Expand All @@ -1023,7 +1018,10 @@ tramp_intern(const Obj_Entry *reqobj, const struct tramp_data *data)
}
end:
lock_release(rtld_tramp_lock, &lockstate);
return (entry);

tramp_check_sig(header, reqobj, data);

return (tramp_make_entry(header));
}

struct func_sig
Expand All @@ -1034,7 +1032,8 @@ sigtab_get(const Obj_Entry *obj, unsigned long symnum)
symnum, obj->path);

if (obj->sigtab == NULL)
return ((struct func_sig) {});
return ((struct func_sig) { .valid = false });

return (obj->sigtab[symnum]);
}

Expand Down
14 changes: 10 additions & 4 deletions libexec/rtld-elf/rtld_c18n.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -172,20 +172,26 @@ struct func_sig {
unsigned char reg_args : 4;
unsigned char valid : 1;
};
_Static_assert(sizeof(struct func_sig) == sizeof(func_sig_int),
"Unexpected func_sig size");

struct tramp_data {
void *target;
const Obj_Entry *defobj;
const Elf_Sym *def;
void *entry;
struct func_sig sig;
};
_Static_assert(sizeof(struct func_sig) == sizeof(func_sig_int),
"Unexpected func_sig size");

struct tramp_header {
void *target;
const Obj_Entry *defobj;
const Elf_Sym *def;
uint32_t entry[];
};

void *tramp_hook(void *, int, void *, const Obj_Entry *, const Elf_Sym *,
void *);
size_t tramp_compile(void **, const struct tramp_data *);
size_t tramp_compile(struct tramp_header **, const struct tramp_data *);
void *tramp_intern(const Obj_Entry *reqobj, const struct tramp_data *);

struct func_sig sigtab_get(const Obj_Entry *, unsigned long);
Expand Down

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