libbpf: Update gen_loader to emit BTF_KIND_FUNC relocations

This change updates the BPF syscall loader to relocate BTF_KIND_FUNC
relocations, with support for weak kfunc relocations. The general idea
is to move map_fds to loader map, and also use the data for storing
kfunc BTF fds. Since both reuse the fd_array parameter, they need to be
kept together.

For map_fds, we reserve MAX_USED_MAPS slots in a region, and for kfunc,
we reserve MAX_KFUNC_DESCS. This is done so that insn->off has more
chances of being <= INT16_MAX than treating data map as a sparse array
and adding fd as needed.

When the MAX_KFUNC_DESCS limit is reached, we fall back to the sparse
array model, so that as long as it does remain <= INT16_MAX, we pass an
index relative to the start of fd_array.

We store all ksyms in an array where we try to avoid calling the
bpf_btf_find_by_name_kind helper, and also reuse the BTF fd that was
already stored. This also speeds up the loading process compared to
emitting calls in all cases, in later tests.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-9-memxor@gmail.com
This commit is contained in:
Kumar Kartikeya Dwivedi 2021-10-02 06:47:56 +05:30 committed by Alexei Starovoitov
parent 466b2e1397
commit 18f4fccbf3
3 changed files with 280 additions and 58 deletions

View File

@ -7,6 +7,15 @@ struct ksym_relo_desc {
const char *name;
int kind;
int insn_idx;
bool is_weak;
};
struct ksym_desc {
const char *name;
int ref;
int kind;
int off;
int insn;
};
struct bpf_gen {
@ -24,6 +33,10 @@ struct bpf_gen {
int relo_cnt;
char attach_target[128];
int attach_kind;
struct ksym_desc *ksyms;
__u32 nr_ksyms;
int fd_array;
int nr_fd_array;
};
void bpf_gen__init(struct bpf_gen *gen, int log_level);
@ -36,6 +49,7 @@ void bpf_gen__prog_load(struct bpf_gen *gen, struct bpf_prog_load_params *load_a
void bpf_gen__map_update_elem(struct bpf_gen *gen, int map_idx, void *value, __u32 value_size);
void bpf_gen__map_freeze(struct bpf_gen *gen, int map_idx);
void bpf_gen__record_attach_target(struct bpf_gen *gen, const char *name, enum bpf_attach_type type);
void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, int kind, int insn_idx);
void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, bool is_weak, int kind,
int insn_idx);
#endif

View File

@ -16,6 +16,8 @@
#define MAX_USED_MAPS 64
#define MAX_USED_PROGS 32
#define MAX_KFUNC_DESCS 256
#define MAX_FD_ARRAY_SZ (MAX_USED_PROGS + MAX_KFUNC_DESCS)
/* The following structure describes the stack layout of the loader program.
* In addition R6 contains the pointer to context.
@ -30,7 +32,6 @@
*/
struct loader_stack {
__u32 btf_fd;
__u32 map_fd[MAX_USED_MAPS];
__u32 prog_fd[MAX_USED_PROGS];
__u32 inner_map_fd;
};
@ -143,13 +144,49 @@ static int add_data(struct bpf_gen *gen, const void *data, __u32 size)
if (realloc_data_buf(gen, size8))
return 0;
prev = gen->data_cur;
if (data) {
memcpy(gen->data_cur, data, size);
gen->data_cur += size;
memcpy(gen->data_cur, &zero, size8 - size);
gen->data_cur += size8 - size;
memcpy(gen->data_cur + size, &zero, size8 - size);
} else {
memset(gen->data_cur, 0, size8);
}
gen->data_cur += size8;
return prev - gen->data_start;
}
/* Get index for map_fd/btf_fd slot in reserved fd_array, or in data relative
* to start of fd_array. Caller can decide if it is usable or not.
*/
static int add_map_fd(struct bpf_gen *gen)
{
if (!gen->fd_array)
gen->fd_array = add_data(gen, NULL, MAX_FD_ARRAY_SZ * sizeof(int));
if (gen->nr_maps == MAX_USED_MAPS) {
pr_warn("Total maps exceeds %d\n", MAX_USED_MAPS);
gen->error = -E2BIG;
return 0;
}
return gen->nr_maps++;
}
static int add_kfunc_btf_fd(struct bpf_gen *gen)
{
int cur;
if (!gen->fd_array)
gen->fd_array = add_data(gen, NULL, MAX_FD_ARRAY_SZ * sizeof(int));
if (gen->nr_fd_array == MAX_KFUNC_DESCS) {
cur = add_data(gen, NULL, sizeof(int));
return (cur - gen->fd_array) / sizeof(int);
}
return MAX_USED_MAPS + gen->nr_fd_array++;
}
static int blob_fd_array_off(struct bpf_gen *gen, int index)
{
return gen->fd_array + index * sizeof(int);
}
static int insn_bytes_to_bpf_size(__u32 sz)
{
switch (sz) {
@ -171,14 +208,22 @@ static void emit_rel_store(struct bpf_gen *gen, int off, int data)
emit(gen, BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0, 0));
}
/* *(u64 *)(blob + off) = (u64)(void *)(%sp + stack_off) */
static void emit_rel_store_sp(struct bpf_gen *gen, int off, int stack_off)
static void move_blob2blob(struct bpf_gen *gen, int off, int size, int blob_off)
{
emit(gen, BPF_MOV64_REG(BPF_REG_0, BPF_REG_10));
emit(gen, BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, stack_off));
emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_2, BPF_PSEUDO_MAP_IDX_VALUE,
0, 0, 0, blob_off));
emit(gen, BPF_LDX_MEM(insn_bytes_to_bpf_size(size), BPF_REG_0, BPF_REG_2, 0));
emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_1, BPF_PSEUDO_MAP_IDX_VALUE,
0, 0, 0, off));
emit(gen, BPF_STX_MEM(BPF_DW, BPF_REG_1, BPF_REG_0, 0));
emit(gen, BPF_STX_MEM(insn_bytes_to_bpf_size(size), BPF_REG_1, BPF_REG_0, 0));
}
static void move_blob2ctx(struct bpf_gen *gen, int ctx_off, int size, int blob_off)
{
emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_1, BPF_PSEUDO_MAP_IDX_VALUE,
0, 0, 0, blob_off));
emit(gen, BPF_LDX_MEM(insn_bytes_to_bpf_size(size), BPF_REG_0, BPF_REG_1, 0));
emit(gen, BPF_STX_MEM(insn_bytes_to_bpf_size(size), BPF_REG_6, BPF_REG_0, ctx_off));
}
static void move_ctx2blob(struct bpf_gen *gen, int off, int size, int ctx_off,
@ -326,11 +371,11 @@ int bpf_gen__finish(struct bpf_gen *gen)
offsetof(struct bpf_prog_desc, prog_fd), 4,
stack_off(prog_fd[i]));
for (i = 0; i < gen->nr_maps; i++)
move_stack2ctx(gen,
move_blob2ctx(gen,
sizeof(struct bpf_loader_ctx) +
sizeof(struct bpf_map_desc) * i +
offsetof(struct bpf_map_desc, map_fd), 4,
stack_off(map_fd[i]));
blob_fd_array_off(gen, i));
emit(gen, BPF_MOV64_IMM(BPF_REG_0, 0));
emit(gen, BPF_EXIT_INSN());
pr_debug("gen: finish %d\n", gen->error);
@ -390,7 +435,7 @@ void bpf_gen__map_create(struct bpf_gen *gen,
{
int attr_size = offsetofend(union bpf_attr, btf_vmlinux_value_type_id);
bool close_inner_map_fd = false;
int map_create_attr;
int map_create_attr, idx;
union bpf_attr attr;
memset(&attr, 0, attr_size);
@ -467,9 +512,11 @@ void bpf_gen__map_create(struct bpf_gen *gen,
gen->error = -EDOM; /* internal bug */
return;
} else {
emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_7,
stack_off(map_fd[map_idx])));
gen->nr_maps++;
/* add_map_fd does gen->nr_maps++ */
idx = add_map_fd(gen);
emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_1, BPF_PSEUDO_MAP_IDX_VALUE,
0, 0, 0, blob_fd_array_off(gen, idx)));
emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_7, 0));
}
if (close_inner_map_fd)
emit_sys_close_stack(gen, stack_off(inner_map_fd));
@ -511,8 +558,8 @@ static void emit_find_attach_target(struct bpf_gen *gen)
*/
}
void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, int kind,
int insn_idx)
void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, bool is_weak,
int kind, int insn_idx)
{
struct ksym_relo_desc *relo;
@ -524,38 +571,192 @@ void bpf_gen__record_extern(struct bpf_gen *gen, const char *name, int kind,
gen->relos = relo;
relo += gen->relo_cnt;
relo->name = name;
relo->is_weak = is_weak;
relo->kind = kind;
relo->insn_idx = insn_idx;
gen->relo_cnt++;
}
static void emit_relo(struct bpf_gen *gen, struct ksym_relo_desc *relo, int insns)
/* returns existing ksym_desc with ref incremented, or inserts a new one */
static struct ksym_desc *get_ksym_desc(struct bpf_gen *gen, struct ksym_relo_desc *relo)
{
int name, insn, len = strlen(relo->name) + 1;
struct ksym_desc *kdesc;
pr_debug("gen: emit_relo: %s at %d\n", relo->name, relo->insn_idx);
name = add_data(gen, relo->name, len);
for (int i = 0; i < gen->nr_ksyms; i++) {
if (!strcmp(gen->ksyms[i].name, relo->name)) {
gen->ksyms[i].ref++;
return &gen->ksyms[i];
}
}
kdesc = libbpf_reallocarray(gen->ksyms, gen->nr_ksyms + 1, sizeof(*kdesc));
if (!kdesc) {
gen->error = -ENOMEM;
return NULL;
}
gen->ksyms = kdesc;
kdesc = &gen->ksyms[gen->nr_ksyms++];
kdesc->name = relo->name;
kdesc->kind = relo->kind;
kdesc->ref = 1;
kdesc->off = 0;
kdesc->insn = 0;
return kdesc;
}
/* Overwrites BPF_REG_{0, 1, 2, 3, 4, 7}
* Returns result in BPF_REG_7
*/
static void emit_bpf_find_by_name_kind(struct bpf_gen *gen, struct ksym_relo_desc *relo)
{
int name_off, len = strlen(relo->name) + 1;
name_off = add_data(gen, relo->name, len);
emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_1, BPF_PSEUDO_MAP_IDX_VALUE,
0, 0, 0, name));
0, 0, 0, name_off));
emit(gen, BPF_MOV64_IMM(BPF_REG_2, len));
emit(gen, BPF_MOV64_IMM(BPF_REG_3, relo->kind));
emit(gen, BPF_MOV64_IMM(BPF_REG_4, 0));
emit(gen, BPF_EMIT_CALL(BPF_FUNC_btf_find_by_name_kind));
emit(gen, BPF_MOV64_REG(BPF_REG_7, BPF_REG_0));
debug_ret(gen, "find_by_name_kind(%s,%d)", relo->name, relo->kind);
}
/* Expects:
* BPF_REG_8 - pointer to instruction
*
* We need to reuse BTF fd for same symbol otherwise each relocation takes a new
* index, while kernel limits total kfunc BTFs to 256. For duplicate symbols,
* this would mean a new BTF fd index for each entry. By pairing symbol name
* with index, we get the insn->imm, insn->off pairing that kernel uses for
* kfunc_tab, which becomes the effective limit even though all of them may
* share same index in fd_array (such that kfunc_btf_tab has 1 element).
*/
static void emit_relo_kfunc_btf(struct bpf_gen *gen, struct ksym_relo_desc *relo, int insn)
{
struct ksym_desc *kdesc;
int btf_fd_idx;
kdesc = get_ksym_desc(gen, relo);
if (!kdesc)
return;
/* try to copy from existing bpf_insn */
if (kdesc->ref > 1) {
move_blob2blob(gen, insn + offsetof(struct bpf_insn, imm), 4,
kdesc->insn + offsetof(struct bpf_insn, imm));
move_blob2blob(gen, insn + offsetof(struct bpf_insn, off), 2,
kdesc->insn + offsetof(struct bpf_insn, off));
goto log;
}
/* remember insn offset, so we can copy BTF ID and FD later */
kdesc->insn = insn;
emit_bpf_find_by_name_kind(gen, relo);
if (!relo->is_weak)
emit_check_err(gen);
/* get index in fd_array to store BTF FD at */
btf_fd_idx = add_kfunc_btf_fd(gen);
if (btf_fd_idx > INT16_MAX) {
pr_warn("BTF fd off %d for kfunc %s exceeds INT16_MAX, cannot process relocation\n",
btf_fd_idx, relo->name);
gen->error = -E2BIG;
return;
}
kdesc->off = btf_fd_idx;
/* set a default value for imm */
emit(gen, BPF_ST_MEM(BPF_W, BPF_REG_8, offsetof(struct bpf_insn, imm), 0));
/* skip success case store if ret < 0 */
emit(gen, BPF_JMP_IMM(BPF_JSLT, BPF_REG_7, 0, 1));
/* store btf_id into insn[insn_idx].imm */
emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_8, BPF_REG_7, offsetof(struct bpf_insn, imm)));
/* load fd_array slot pointer */
emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_0, BPF_PSEUDO_MAP_IDX_VALUE,
0, 0, 0, blob_fd_array_off(gen, btf_fd_idx)));
/* skip store of BTF fd if ret < 0 */
emit(gen, BPF_JMP_IMM(BPF_JSLT, BPF_REG_7, 0, 3));
/* store BTF fd in slot */
emit(gen, BPF_MOV64_REG(BPF_REG_9, BPF_REG_7));
emit(gen, BPF_ALU64_IMM(BPF_RSH, BPF_REG_9, 32));
emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_0, BPF_REG_9, 0));
/* set a default value for off */
emit(gen, BPF_ST_MEM(BPF_H, BPF_REG_8, offsetof(struct bpf_insn, off), 0));
/* skip insn->off store if ret < 0 */
emit(gen, BPF_JMP_IMM(BPF_JSLT, BPF_REG_7, 0, 2));
/* skip if vmlinux BTF */
emit(gen, BPF_JMP_IMM(BPF_JEQ, BPF_REG_9, 0, 1));
/* store index into insn[insn_idx].off */
emit(gen, BPF_ST_MEM(BPF_H, BPF_REG_8, offsetof(struct bpf_insn, off), btf_fd_idx));
log:
if (!gen->log_level)
return;
emit(gen, BPF_LDX_MEM(BPF_W, BPF_REG_7, BPF_REG_8,
offsetof(struct bpf_insn, imm)));
emit(gen, BPF_LDX_MEM(BPF_H, BPF_REG_9, BPF_REG_8,
offsetof(struct bpf_insn, off)));
debug_regs(gen, BPF_REG_7, BPF_REG_9, " func (%s:count=%d): imm: %%d, off: %%d",
relo->name, kdesc->ref);
emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_0, BPF_PSEUDO_MAP_IDX_VALUE,
0, 0, 0, blob_fd_array_off(gen, kdesc->off)));
emit(gen, BPF_LDX_MEM(BPF_W, BPF_REG_9, BPF_REG_0, 0));
debug_regs(gen, BPF_REG_9, -1, " func (%s:count=%d): btf_fd",
relo->name, kdesc->ref);
}
/* Expects:
* BPF_REG_8 - pointer to instruction
*/
static void emit_relo_ksym_btf(struct bpf_gen *gen, struct ksym_relo_desc *relo, int insn)
{
struct ksym_desc *kdesc;
kdesc = get_ksym_desc(gen, relo);
if (!kdesc)
return;
/* try to copy from existing ldimm64 insn */
if (kdesc->ref > 1) {
move_blob2blob(gen, insn + offsetof(struct bpf_insn, imm), 4,
kdesc->insn + offsetof(struct bpf_insn, imm));
move_blob2blob(gen, insn + sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm), 4,
kdesc->insn + sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm));
goto log;
}
/* remember insn offset, so we can copy BTF ID and FD later */
kdesc->insn = insn;
emit_bpf_find_by_name_kind(gen, relo);
emit_check_err(gen);
/* store btf_id into insn[insn_idx].imm */
insn = insns + sizeof(struct bpf_insn) * relo->insn_idx +
offsetof(struct bpf_insn, imm);
emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_0, BPF_PSEUDO_MAP_IDX_VALUE,
0, 0, 0, insn));
emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_0, BPF_REG_7, 0));
if (relo->kind == BTF_KIND_VAR) {
emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_8, BPF_REG_7, offsetof(struct bpf_insn, imm)));
/* store btf_obj_fd into insn[insn_idx + 1].imm */
emit(gen, BPF_ALU64_IMM(BPF_RSH, BPF_REG_7, 32));
emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_0, BPF_REG_7,
sizeof(struct bpf_insn)));
emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_8, BPF_REG_7,
sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm)));
log:
if (!gen->log_level)
return;
emit(gen, BPF_LDX_MEM(BPF_W, BPF_REG_7, BPF_REG_8,
offsetof(struct bpf_insn, imm)));
emit(gen, BPF_LDX_MEM(BPF_H, BPF_REG_9, BPF_REG_8, sizeof(struct bpf_insn) +
offsetof(struct bpf_insn, imm)));
debug_regs(gen, BPF_REG_7, BPF_REG_9, " var (%s:count=%d): imm: %%d, fd: %%d",
relo->name, kdesc->ref);
}
static void emit_relo(struct bpf_gen *gen, struct ksym_relo_desc *relo, int insns)
{
int insn;
pr_debug("gen: emit_relo (%d): %s at %d\n", relo->kind, relo->name, relo->insn_idx);
insn = insns + sizeof(struct bpf_insn) * relo->insn_idx;
emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_8, BPF_PSEUDO_MAP_IDX_VALUE, 0, 0, 0, insn));
switch (relo->kind) {
case BTF_KIND_VAR:
emit_relo_ksym_btf(gen, relo, insn);
break;
case BTF_KIND_FUNC:
emit_relo_kfunc_btf(gen, relo, insn);
break;
default:
pr_warn("Unknown relocation kind '%d'\n", relo->kind);
gen->error = -EDOM;
return;
}
}
@ -571,14 +772,22 @@ static void cleanup_relos(struct bpf_gen *gen, int insns)
{
int i, insn;
for (i = 0; i < gen->relo_cnt; i++) {
if (gen->relos[i].kind != BTF_KIND_VAR)
continue;
for (i = 0; i < gen->nr_ksyms; i++) {
if (gen->ksyms[i].kind == BTF_KIND_VAR) {
/* close fd recorded in insn[insn_idx + 1].imm */
insn = insns +
sizeof(struct bpf_insn) * (gen->relos[i].insn_idx + 1) +
offsetof(struct bpf_insn, imm);
insn = gen->ksyms[i].insn;
insn += sizeof(struct bpf_insn) + offsetof(struct bpf_insn, imm);
emit_sys_close_blob(gen, insn);
} else { /* BTF_KIND_FUNC */
emit_sys_close_blob(gen, blob_fd_array_off(gen, gen->ksyms[i].off));
if (gen->ksyms[i].off < MAX_FD_ARRAY_SZ)
gen->nr_fd_array--;
}
}
if (gen->nr_ksyms) {
free(gen->ksyms);
gen->nr_ksyms = 0;
gen->ksyms = NULL;
}
if (gen->relo_cnt) {
free(gen->relos);
@ -637,9 +846,8 @@ void bpf_gen__prog_load(struct bpf_gen *gen,
/* populate union bpf_attr with a pointer to line_info */
emit_rel_store(gen, attr_field(prog_load_attr, line_info), line_info);
/* populate union bpf_attr fd_array with a pointer to stack where map_fds are saved */
emit_rel_store_sp(gen, attr_field(prog_load_attr, fd_array),
stack_off(map_fd[0]));
/* populate union bpf_attr fd_array with a pointer to data where map_fds are saved */
emit_rel_store(gen, attr_field(prog_load_attr, fd_array), gen->fd_array);
/* populate union bpf_attr with user provided log details */
move_ctx2blob(gen, attr_field(prog_load_attr, log_level), 4,
@ -706,8 +914,8 @@ void bpf_gen__map_update_elem(struct bpf_gen *gen, int map_idx, void *pvalue,
emit(gen, BPF_EMIT_CALL(BPF_FUNC_copy_from_user));
map_update_attr = add_data(gen, &attr, attr_size);
move_stack2blob(gen, attr_field(map_update_attr, map_fd), 4,
stack_off(map_fd[map_idx]));
move_blob2blob(gen, attr_field(map_update_attr, map_fd), 4,
blob_fd_array_off(gen, map_idx));
emit_rel_store(gen, attr_field(map_update_attr, key), key);
emit_rel_store(gen, attr_field(map_update_attr, value), value);
/* emit MAP_UPDATE_ELEM command */
@ -725,8 +933,8 @@ void bpf_gen__map_freeze(struct bpf_gen *gen, int map_idx)
memset(&attr, 0, attr_size);
pr_debug("gen: map_freeze: idx %d\n", map_idx);
map_freeze_attr = add_data(gen, &attr, attr_size);
move_stack2blob(gen, attr_field(map_freeze_attr, map_fd), 4,
stack_off(map_fd[map_idx]));
move_blob2blob(gen, attr_field(map_freeze_attr, map_fd), 4,
blob_fd_array_off(gen, map_idx));
/* emit MAP_FREEZE command */
emit_sys_bpf(gen, BPF_MAP_FREEZE, map_freeze_attr, attr_size);
debug_ret(gen, "map_freeze");

View File

@ -6360,12 +6360,12 @@ static int bpf_program__record_externs(struct bpf_program *prog)
ext->name);
return -ENOTSUP;
}
bpf_gen__record_extern(obj->gen_loader, ext->name, BTF_KIND_VAR,
relo->insn_idx);
bpf_gen__record_extern(obj->gen_loader, ext->name, ext->is_weak,
BTF_KIND_VAR, relo->insn_idx);
break;
case RELO_EXTERN_FUNC:
bpf_gen__record_extern(obj->gen_loader, ext->name, BTF_KIND_FUNC,
relo->insn_idx);
bpf_gen__record_extern(obj->gen_loader, ext->name, ext->is_weak,
BTF_KIND_FUNC, relo->insn_idx);
break;
default:
continue;