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bpf: Pass a set of bpf_core_relo-s to prog_load command.

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struct bpf_core_relo is generated by llvm and processed by libbpf.
It's a de-facto uapi.
With CO-RE in the kernel the struct bpf_core_relo becomes uapi de-jure.
Add an ability to pass a set of 'struct bpf_core_relo' to prog_load command
and let the kernel perform CO-RE relocations.

Note the struct bpf_line_info and struct bpf_func_info have the same
layout when passed from LLVM to libbpf and from libbpf to the kernel
except "insn_off" fields means "byte offset" when LLVM generates it.
Then libbpf converts it to "insn index" to pass to the kernel.
The struct bpf_core_relo's "insn_off" field is always "byte offset".

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20211201181040.23337-6-alexei.starovoitov@gmail.com
This commit is contained in:
Alexei Starovoitov 2021-12-01 10:10:28 -08:00 committed by Andrii Nakryiko
parent 46334a0cd2
commit fbd94c7afc
7 changed files with 207 additions and 56 deletions
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8
include/linux/bpf.h
View file

@ -1732,6 +1732,14 @@ bool bpf_prog_has_kfunc_call(const struct bpf_prog *prog);
const struct btf_func_model *
bpf_jit_find_kfunc_model(const struct bpf_prog *prog,
const struct bpf_insn *insn);
struct bpf_core_ctx {
struct bpf_verifier_log *log;
const struct btf *btf;
};
int bpf_core_apply(struct bpf_core_ctx *ctx, const struct bpf_core_relo *relo,
int relo_idx, void *insn);
#else /* !CONFIG_BPF_SYSCALL */
static inline struct bpf_prog *bpf_prog_get(u32 ufd)
{

59
include/uapi/linux/bpf.h
View file

@ -1342,8 +1342,10 @@ union bpf_attr {
/* or valid module BTF object fd or 0 to attach to vmlinux */
__u32 attach_btf_obj_fd;
};
__u32 :32; /* pad */
__u32 core_relo_cnt; /* number of bpf_core_relo */
__aligned_u64 fd_array; /* array of FDs */
__aligned_u64 core_relos;
__u32 core_relo_rec_size; /* sizeof(struct bpf_core_relo) */
};
struct { /* anonymous struct used by BPF_OBJ_* commands */
@ -6393,4 +6395,59 @@ enum bpf_core_relo_kind {
BPF_CORE_ENUMVAL_VALUE = 11, /* enum value integer value */
};
/*
* "struct bpf_core_relo" is used to pass relocation data form LLVM to libbpf
* and from libbpf to the kernel.
*
* CO-RE relocation captures the following data:
* - insn_off - instruction offset (in bytes) within a BPF program that needs
* its insn->imm field to be relocated with actual field info;
* - type_id - BTF type ID of the "root" (containing) entity of a relocatable
* type or field;
* - access_str_off - offset into corresponding .BTF string section. String
* interpretation depends on specific relocation kind:
* - for field-based relocations, string encodes an accessed field using
* a sequence of field and array indices, separated by colon (:). It's
* conceptually very close to LLVM's getelementptr ([0]) instruction's
* arguments for identifying offset to a field.
* - for type-based relocations, strings is expected to be just "0";
* - for enum value-based relocations, string contains an index of enum
* value within its enum type;
* - kind - one of enum bpf_core_relo_kind;
*
* Example:
* struct sample {
* int a;
* struct {
* int b[10];
* };
* };
*
* struct sample *s = ...;
* int *x = &s->a; // encoded as "0:0" (a is field #0)
* int *y = &s->b[5]; // encoded as "0:1:0:5" (anon struct is field #1,
* // b is field #0 inside anon struct, accessing elem #5)
* int *z = &s[10]->b; // encoded as "10:1" (ptr is used as an array)
*
* type_id for all relocs in this example will capture BTF type id of
* `struct sample`.
*
* Such relocation is emitted when using __builtin_preserve_access_index()
* Clang built-in, passing expression that captures field address, e.g.:
*
* bpf_probe_read(&dst, sizeof(dst),
* __builtin_preserve_access_index(&src->a.b.c));
*
* In this case Clang will emit field relocation recording necessary data to
* be able to find offset of embedded `a.b.c` field within `src` struct.
*
* [0] https://llvm.org/docs/LangRef.html#getelementptr-instruction
*/
struct bpf_core_relo {
__u32 insn_off;
__u32 type_id;
__u32 access_str_off;
enum bpf_core_relo_kind kind;
};
#endif /* _UAPI__LINUX_BPF_H__ */

6
kernel/bpf/btf.c
View file

@ -6439,3 +6439,9 @@ size_t bpf_core_essential_name_len(const char *name)
}
return n;
}
int bpf_core_apply(struct bpf_core_ctx *ctx, const struct bpf_core_relo *relo,
int relo_idx, void *insn)
{
return -EOPNOTSUPP;
}

2
kernel/bpf/syscall.c
View file

@ -2184,7 +2184,7 @@ static bool is_perfmon_prog_type(enum bpf_prog_type prog_type)
}
/* last field in 'union bpf_attr' used by this command */
#define BPF_PROG_LOAD_LAST_FIELD fd_array
#define BPF_PROG_LOAD_LAST_FIELD core_relo_rec_size
static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr)
{

76
kernel/bpf/verifier.c
View file

@ -10273,6 +10273,78 @@ static int check_btf_line(struct bpf_verifier_env *env,
return err;
}
#define MIN_CORE_RELO_SIZE sizeof(struct bpf_core_relo)
#define MAX_CORE_RELO_SIZE MAX_FUNCINFO_REC_SIZE
static int check_core_relo(struct bpf_verifier_env *env,
const union bpf_attr *attr,
bpfptr_t uattr)
{
u32 i, nr_core_relo, ncopy, expected_size, rec_size;
struct bpf_core_relo core_relo = {};
struct bpf_prog *prog = env->prog;
const struct btf *btf = prog->aux->btf;
struct bpf_core_ctx ctx = {
.log = &env->log,
.btf = btf,
};
bpfptr_t u_core_relo;
int err;
nr_core_relo = attr->core_relo_cnt;
if (!nr_core_relo)
return 0;
if (nr_core_relo > INT_MAX / sizeof(struct bpf_core_relo))
return -EINVAL;
rec_size = attr->core_relo_rec_size;
if (rec_size < MIN_CORE_RELO_SIZE ||
rec_size > MAX_CORE_RELO_SIZE ||
rec_size % sizeof(u32))
return -EINVAL;
u_core_relo = make_bpfptr(attr->core_relos, uattr.is_kernel);
expected_size = sizeof(struct bpf_core_relo);
ncopy = min_t(u32, expected_size, rec_size);
/* Unlike func_info and line_info, copy and apply each CO-RE
* relocation record one at a time.
*/
for (i = 0; i < nr_core_relo; i++) {
/* future proofing when sizeof(bpf_core_relo) changes */
err = bpf_check_uarg_tail_zero(u_core_relo, expected_size, rec_size);
if (err) {
if (err == -E2BIG) {
verbose(env, "nonzero tailing record in core_relo");
if (copy_to_bpfptr_offset(uattr,
offsetof(union bpf_attr, core_relo_rec_size),
&expected_size, sizeof(expected_size)))
err = -EFAULT;
}
break;
}
if (copy_from_bpfptr(&core_relo, u_core_relo, ncopy)) {
err = -EFAULT;
break;
}
if (core_relo.insn_off % 8 || core_relo.insn_off / 8 >= prog->len) {
verbose(env, "Invalid core_relo[%u].insn_off:%u prog->len:%u\n",
i, core_relo.insn_off, prog->len);
err = -EINVAL;
break;
}
err = bpf_core_apply(&ctx, &core_relo, i,
&prog->insnsi[core_relo.insn_off / 8]);
if (err)
break;
bpfptr_add(&u_core_relo, rec_size);
}
return err;
}
static int check_btf_info(struct bpf_verifier_env *env,
const union bpf_attr *attr,
bpfptr_t uattr)
@ -10303,6 +10375,10 @@ static int check_btf_info(struct bpf_verifier_env *env,
if (err)
return err;
err = check_core_relo(env, attr, uattr);
if (err)
return err;
return 0;
}

59
tools/include/uapi/linux/bpf.h
View file

@ -1342,8 +1342,10 @@ union bpf_attr {
/* or valid module BTF object fd or 0 to attach to vmlinux */
__u32 attach_btf_obj_fd;
};
__u32 :32; /* pad */
__u32 core_relo_cnt; /* number of bpf_core_relo */
__aligned_u64 fd_array; /* array of FDs */
__aligned_u64 core_relos;
__u32 core_relo_rec_size; /* sizeof(struct bpf_core_relo) */
};
struct { /* anonymous struct used by BPF_OBJ_* commands */
@ -6393,4 +6395,59 @@ enum bpf_core_relo_kind {
BPF_CORE_ENUMVAL_VALUE = 11, /* enum value integer value */
};
/*
* "struct bpf_core_relo" is used to pass relocation data form LLVM to libbpf
* and from libbpf to the kernel.
*
* CO-RE relocation captures the following data:
* - insn_off - instruction offset (in bytes) within a BPF program that needs
* its insn->imm field to be relocated with actual field info;
* - type_id - BTF type ID of the "root" (containing) entity of a relocatable
* type or field;
* - access_str_off - offset into corresponding .BTF string section. String
* interpretation depends on specific relocation kind:
* - for field-based relocations, string encodes an accessed field using
* a sequence of field and array indices, separated by colon (:). It's
* conceptually very close to LLVM's getelementptr ([0]) instruction's
* arguments for identifying offset to a field.
* - for type-based relocations, strings is expected to be just "0";
* - for enum value-based relocations, string contains an index of enum
* value within its enum type;
* - kind - one of enum bpf_core_relo_kind;
*
* Example:
* struct sample {
* int a;
* struct {
* int b[10];
* };
* };
*
* struct sample *s = ...;
* int *x = &s->a; // encoded as "0:0" (a is field #0)
* int *y = &s->b[5]; // encoded as "0:1:0:5" (anon struct is field #1,
* // b is field #0 inside anon struct, accessing elem #5)
* int *z = &s[10]->b; // encoded as "10:1" (ptr is used as an array)
*
* type_id for all relocs in this example will capture BTF type id of
* `struct sample`.
*
* Such relocation is emitted when using __builtin_preserve_access_index()
* Clang built-in, passing expression that captures field address, e.g.:
*
* bpf_probe_read(&dst, sizeof(dst),
* __builtin_preserve_access_index(&src->a.b.c));
*
* In this case Clang will emit field relocation recording necessary data to
* be able to find offset of embedded `a.b.c` field within `src` struct.
*
* [0] https://llvm.org/docs/LangRef.html#getelementptr-instruction
*/
struct bpf_core_relo {
__u32 insn_off;
__u32 type_id;
__u32 access_str_off;
enum bpf_core_relo_kind kind;
};
#endif /* _UAPI__LINUX_BPF_H__ */

53
tools/lib/bpf/relo_core.h
View file

@ -6,59 +6,6 @@
#include <linux/bpf.h>
/* The minimum bpf_core_relo checked by the loader
*
* CO-RE relocation captures the following data:
* - insn_off - instruction offset (in bytes) within a BPF program that needs
* its insn->imm field to be relocated with actual field info;
* - type_id - BTF type ID of the "root" (containing) entity of a relocatable
* type or field;
* - access_str_off - offset into corresponding .BTF string section. String
* interpretation depends on specific relocation kind:
* - for field-based relocations, string encodes an accessed field using
* a sequence of field and array indices, separated by colon (:). It's
* conceptually very close to LLVM's getelementptr ([0]) instruction's
* arguments for identifying offset to a field.
* - for type-based relocations, strings is expected to be just "0";
* - for enum value-based relocations, string contains an index of enum
* value within its enum type;
*
* Example to provide a better feel.
*
* struct sample {
* int a;
* struct {
* int b[10];
* };
* };
*
* struct sample *s = ...;
* int x = &s->a; // encoded as "0:0" (a is field #0)
* int y = &s->b[5]; // encoded as "0:1:0:5" (anon struct is field #1,
* // b is field #0 inside anon struct, accessing elem #5)
* int z = &s[10]->b; // encoded as "10:1" (ptr is used as an array)
*
* type_id for all relocs in this example will capture BTF type id of
* `struct sample`.
*
* Such relocation is emitted when using __builtin_preserve_access_index()
* Clang built-in, passing expression that captures field address, e.g.:
*
* bpf_probe_read(&dst, sizeof(dst),
* __builtin_preserve_access_index(&src->a.b.c));
*
* In this case Clang will emit field relocation recording necessary data to
* be able to find offset of embedded `a.b.c` field within `src` struct.
*
* [0] https://llvm.org/docs/LangRef.html#getelementptr-instruction
*/
struct bpf_core_relo {
__u32 insn_off;
__u32 type_id;
__u32 access_str_off;
enum bpf_core_relo_kind kind;
};
struct bpf_core_cand {
const struct btf *btf;
const struct btf_type *t;