[PATCH bpf-next v4 4/6] bpf: Introduce bpf_per_cpu_ptr()

Hao Luo
2020-09-29T23:51:25Z

Add bpf_per_cpu_ptr() to help bpf programs access percpu vars.
bpf_per_cpu_ptr() has the same semantic as per_cpu_ptr() in the kernel
except that it may return NULL. This happens when the cpu parameter is
out of range. So the caller must check the returned value.

Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Hao Luo <haoluo@google.com>
---
include/linux/bpf.h | 4 +++
include/linux/btf.h | 11 ++++++
include/uapi/linux/bpf.h | 18 ++++++++++
kernel/bpf/btf.c | 10 ------
kernel/bpf/helpers.c | 18 ++++++++++
kernel/bpf/verifier.c | 64 ++++++++++++++++++++++++++++++++--
kernel/trace/bpf_trace.c | 2 ++
tools/include/uapi/linux/bpf.h | 18 ++++++++++
8 files changed, 132 insertions(+), 13 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 50e5c4b52bd1..9dde15b2479d 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -293,6 +293,7 @@ enum bpf_arg_type {
ARG_PTR_TO_ALLOC_MEM_OR_NULL, /* pointer to dynamically allocated memory or NULL */
ARG_CONST_ALLOC_SIZE_OR_ZERO, /* number of allocated bytes requested */
ARG_PTR_TO_BTF_ID_SOCK_COMMON, /* pointer to in-kernel sock_common or bpf-mirrored bpf_sock */
+ ARG_PTR_TO_PERCPU_BTF_ID, /* pointer to in-kernel percpu type */
__BPF_ARG_TYPE_MAX,
};

@@ -307,6 +308,7 @@ enum bpf_return_type {
RET_PTR_TO_SOCK_COMMON_OR_NULL, /* returns a pointer to a sock_common or NULL */
RET_PTR_TO_ALLOC_MEM_OR_NULL, /* returns a pointer to dynamically allocated memory or NULL */
RET_PTR_TO_BTF_ID_OR_NULL, /* returns a pointer to a btf_id or NULL */
+ RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL, /* returns a pointer to a valid memory or a btf_id or NULL */
};

/* eBPF function prototype used by verifier to allow BPF_CALLs from eBPF programs
@@ -405,6 +407,7 @@ enum bpf_reg_type {
PTR_TO_RDONLY_BUF_OR_NULL, /* reg points to a readonly buffer or NULL */
PTR_TO_RDWR_BUF, /* reg points to a read/write buffer */
PTR_TO_RDWR_BUF_OR_NULL, /* reg points to a read/write buffer or NULL */
+ PTR_TO_PERCPU_BTF_ID, /* reg points to a percpu kernel variable */
};

/* The information passed from prog-specific *_is_valid_access
@@ -1828,6 +1831,7 @@ extern const struct bpf_func_proto bpf_skc_to_tcp_request_sock_proto;
extern const struct bpf_func_proto bpf_skc_to_udp6_sock_proto;
extern const struct bpf_func_proto bpf_copy_from_user_proto;
extern const struct bpf_func_proto bpf_snprintf_btf_proto;
+extern const struct bpf_func_proto bpf_per_cpu_ptr_proto;

const struct bpf_func_proto *bpf_tracing_func_proto(
enum bpf_func_id func_id, const struct bpf_prog *prog);
diff --git a/include/linux/btf.h b/include/linux/btf.h
index af1244180588..2bf641829664 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -110,6 +110,11 @@ btf_resolve_size(const struct btf *btf, const struct btf_type *type,
i < btf_type_vlen(struct_type); \
i++, member++)

+#define for_each_vsi(i, datasec_type, member) \
+ for (i = 0, member = btf_type_var_secinfo(datasec_type); \
+ i < btf_type_vlen(datasec_type); \
+ i++, member++)
+
static inline bool btf_type_is_ptr(const struct btf_type *t)
{
return BTF_INFO_KIND(t->info) == BTF_KIND_PTR;
@@ -194,6 +199,12 @@ static inline const struct btf_member *btf_type_member(const struct btf_type *t)
return (const struct btf_member *)(t + 1);
}

+static inline const struct btf_var_secinfo *btf_type_var_secinfo(
+ const struct btf_type *t)
+{
+ return (const struct btf_var_secinfo *)(t + 1);
+}
+
#ifdef CONFIG_BPF_SYSCALL
const struct btf_type *btf_type_by_id(const struct btf *btf, u32 type_id);
const char *btf_name_by_offset(const struct btf *btf, u32 offset);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 1defa5f23078..feae87eaa8c6 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -3661,6 +3661,23 @@ union bpf_attr {
* *flags* are identical to those used for bpf_snprintf_btf.
* Return
* 0 on success or a negative error in case of failure.
+ *
+ * void *bpf_per_cpu_ptr(const void *percpu_ptr, u32 cpu)
+ * Description
+ * Take a pointer to a percpu ksym, *percpu_ptr*, and return a
+ * pointer to the percpu kernel variable on *cpu*. A ksym is an
+ * extern variable decorated with '__ksym'. For ksym, there is a
+ * global var (either static or global) defined of the same name
+ * in the kernel. The ksym is percpu if the global var is percpu.
+ * The returned pointer points to the global percpu var on *cpu*.
+ *
+ * bpf_per_cpu_ptr() has the same semantic as per_cpu_ptr() in the
+ * kernel, except that bpf_per_cpu_ptr() may return NULL. This
+ * happens if *cpu* is larger than nr_cpu_ids. The caller of
+ * bpf_per_cpu_ptr() must check the returned value.
+ * Return
+ * A pointer pointing to the kernel percpu variable on *cpu*, or
+ * NULL, if *cpu* is invalid.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3814,6 +3831,7 @@ union bpf_attr {
FN(copy_from_user), \
FN(snprintf_btf), \
FN(seq_printf_btf), \
+ FN(bpf_per_cpu_ptr), \
/* */

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 00569afe3d0d..ed7d02e8bc93 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -188,11 +188,6 @@
i < btf_type_vlen(struct_type); \
i++, member++)

-#define for_each_vsi(i, struct_type, member) \
- for (i = 0, member = btf_type_var_secinfo(struct_type); \
- i < btf_type_vlen(struct_type); \
- i++, member++)
-
#define for_each_vsi_from(i, from, struct_type, member) \
for (i = from, member = btf_type_var_secinfo(struct_type) + from; \
i < btf_type_vlen(struct_type); \
@@ -598,11 +593,6 @@ static const struct btf_var *btf_type_var(const struct btf_type *t)
return (const struct btf_var *)(t + 1);
}

-static const struct btf_var_secinfo *btf_type_var_secinfo(const struct btf_type *t)
-{
- return (const struct btf_var_secinfo *)(t + 1);
-}
-
static const struct btf_kind_operations *btf_type_ops(const struct btf_type *t)
{
return kind_ops[BTF_INFO_KIND(t->info)];
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index e825441781ab..14fe3f64fd82 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -623,6 +623,22 @@ const struct bpf_func_proto bpf_copy_from_user_proto = {
.arg3_type = ARG_ANYTHING,
};

+BPF_CALL_2(bpf_per_cpu_ptr, const void *, ptr, u32, cpu)
+{
+ if (cpu >= nr_cpu_ids)
+ return (unsigned long)NULL;
+
+ return (unsigned long)per_cpu_ptr((const void __percpu *)ptr, cpu);
+}
+
+const struct bpf_func_proto bpf_per_cpu_ptr_proto = {
+ .func = bpf_per_cpu_ptr,
+ .gpl_only = false,
+ .ret_type = RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL,
+ .arg1_type = ARG_PTR_TO_PERCPU_BTF_ID,
+ .arg2_type = ARG_ANYTHING,
+};
+
const struct bpf_func_proto bpf_get_current_task_proto __weak;
const struct bpf_func_proto bpf_probe_read_user_proto __weak;
const struct bpf_func_proto bpf_probe_read_user_str_proto __weak;
@@ -689,6 +705,8 @@ bpf_base_func_proto(enum bpf_func_id func_id)
return &bpf_snprintf_btf_proto;
case BPF_FUNC_jiffies64:
return &bpf_jiffies64_proto;
+ case BPF_FUNC_bpf_per_cpu_ptr:
+ return &bpf_per_cpu_ptr_proto;
default:
break;
}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fe4965079773..216b8ece23ce 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -238,6 +238,8 @@ struct bpf_call_arg_meta {
u64 msize_max_value;
int ref_obj_id;
int func_id;
+ u32 btf_id;
+ u32 ret_btf_id;
};

struct btf *btf_vmlinux;
@@ -517,6 +519,7 @@ static const char * const reg_type_str[] = {
[PTR_TO_XDP_SOCK] = "xdp_sock",
[PTR_TO_BTF_ID] = "ptr_",
[PTR_TO_BTF_ID_OR_NULL] = "ptr_or_null_",
+ [PTR_TO_PERCPU_BTF_ID] = "percpu_ptr_",
[PTR_TO_MEM] = "mem",
[PTR_TO_MEM_OR_NULL] = "mem_or_null",
[PTR_TO_RDONLY_BUF] = "rdonly_buf",
@@ -583,7 +586,9 @@ static void print_verifier_state(struct bpf_verifier_env *env,
/* reg->off should be 0 for SCALAR_VALUE */
verbose(env, "%lld", reg->var_off.value + reg->off);
} else {
- if (t == PTR_TO_BTF_ID || t == PTR_TO_BTF_ID_OR_NULL)
+ if (t == PTR_TO_BTF_ID ||
+ t == PTR_TO_BTF_ID_OR_NULL ||
+ t == PTR_TO_PERCPU_BTF_ID)
verbose(env, "%s", kernel_type_name(reg->btf_id));
verbose(env, "(id=%d", reg->id);
if (reg_type_may_be_refcounted_or_null(t))
@@ -2204,6 +2209,7 @@ static bool is_spillable_regtype(enum bpf_reg_type type)
case PTR_TO_RDONLY_BUF_OR_NULL:
case PTR_TO_RDWR_BUF:
case PTR_TO_RDWR_BUF_OR_NULL:
+ case PTR_TO_PERCPU_BTF_ID:
return true;
default:
return false;
@@ -4017,6 +4023,7 @@ static const struct bpf_reg_types alloc_mem_types = { .types = { PTR_TO_MEM } };
static const struct bpf_reg_types const_map_ptr_types = { .types = { CONST_PTR_TO_MAP } };
static const struct bpf_reg_types btf_ptr_types = { .types = { PTR_TO_BTF_ID } };
static const struct bpf_reg_types spin_lock_types = { .types = { PTR_TO_MAP_VALUE } };
+static const struct bpf_reg_types percpu_btf_ptr_types = { .types = { PTR_TO_PERCPU_BTF_ID } };

static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
[ARG_PTR_TO_MAP_KEY] = &map_key_value_types,
@@ -4042,6 +4049,7 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
[ARG_PTR_TO_ALLOC_MEM_OR_NULL] = &alloc_mem_types,
[ARG_PTR_TO_INT] = &int_ptr_types,
[ARG_PTR_TO_LONG] = &int_ptr_types,
+ [ARG_PTR_TO_PERCPU_BTF_ID] = &percpu_btf_ptr_types,
};

static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
@@ -4205,6 +4213,12 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
err = check_helper_mem_access(env, regno,
meta->map_ptr->value_size, false,
meta);
+ } else if (arg_type == ARG_PTR_TO_PERCPU_BTF_ID) {
+ if (!reg->btf_id) {
+ verbose(env, "Helper has invalid btf_id in R%d\n", regno);
+ return -EACCES;
+ }
+ meta->ret_btf_id = reg->btf_id;
} else if (arg_type == ARG_PTR_TO_SPIN_LOCK) {
if (meta->func_id == BPF_FUNC_spin_lock) {
if (process_spin_lock(env, regno, true))
@@ -5114,6 +5128,30 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
regs[BPF_REG_0].type = PTR_TO_MEM_OR_NULL;
regs[BPF_REG_0].id = ++env->id_gen;
regs[BPF_REG_0].mem_size = meta.mem_size;
+ } else if (fn->ret_type == RET_PTR_TO_MEM_OR_BTF_ID_OR_NULL) {
+ const struct btf_type *t;
+
+ mark_reg_known_zero(env, regs, BPF_REG_0);
+ t = btf_type_skip_modifiers(btf_vmlinux, meta.ret_btf_id, NULL);
+ if (!btf_type_is_struct(t)) {
+ u32 tsize;
+ const struct btf_type *ret;
+ const char *tname;
+
+ /* resolve the type size of ksym. */
+ ret = btf_resolve_size(btf_vmlinux, t, &tsize);
+ if (IS_ERR(ret)) {
+ tname = btf_name_by_offset(btf_vmlinux, t->name_off);
+ verbose(env, "unable to resolve the size of type '%s': %ld\n",
+ tname, PTR_ERR(ret));
+ return -EINVAL;
+ }
+ regs[BPF_REG_0].type = PTR_TO_MEM_OR_NULL;
+ regs[BPF_REG_0].mem_size = tsize;
+ } else {
+ regs[BPF_REG_0].type = PTR_TO_BTF_ID_OR_NULL;
+ regs[BPF_REG_0].btf_id = meta.ret_btf_id;
+ }
} else if (fn->ret_type == RET_PTR_TO_BTF_ID_OR_NULL) {
int ret_btf_id;

@@ -7523,6 +7561,7 @@ static int check_ld_imm(struct bpf_verifier_env *env, struct bpf_insn *insn)
dst_reg->mem_size = aux->btf_var.mem_size;
break;
case PTR_TO_BTF_ID:
+ case PTR_TO_PERCPU_BTF_ID:
dst_reg->btf_id = aux->btf_var.btf_id;
break;
default:
@@ -9449,10 +9488,14 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,
struct bpf_insn *insn,
struct bpf_insn_aux_data *aux)
{
- u32 type, id = insn->imm;
+ u32 datasec_id, type, id = insn->imm;
+ const struct btf_var_secinfo *vsi;
+ const struct btf_type *datasec;
const struct btf_type *t;
const char *sym_name;
+ bool percpu = false;
u64 addr;
+ int i;

if (!btf_vmlinux) {
verbose(env, "kernel is missing BTF, make sure CONFIG_DEBUG_INFO_BTF=y is specified in Kconfig.\n");
@@ -9484,12 +9527,27 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,
return -ENOENT;
}

+ datasec_id = btf_find_by_name_kind(btf_vmlinux, ".data..percpu",
+ BTF_KIND_DATASEC);
+ if (datasec_id > 0) {
+ datasec = btf_type_by_id(btf_vmlinux, datasec_id);
+ for_each_vsi(i, datasec, vsi) {
+ if (vsi->type == id) {
+ percpu = true;
+ break;
+ }
+ }
+ }
+
insn[0].imm = (u32)addr;
insn[1].imm = addr >> 32;

type = t->type;
t = btf_type_skip_modifiers(btf_vmlinux, type, NULL);
- if (!btf_type_is_struct(t)) {
+ if (percpu) {
+ aux->btf_var.reg_type = PTR_TO_PERCPU_BTF_ID;
+ aux->btf_var.btf_id = type;
+ } else if (!btf_type_is_struct(t)) {
const struct btf_type *ret;
const char *tname;
u32 tsize;
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index e118a83439c3..364a322e2898 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1327,6 +1327,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return prog->aux->sleepable ? &bpf_copy_from_user_proto : NULL;
case BPF_FUNC_snprintf_btf:
return &bpf_snprintf_btf_proto;
+ case BPF_FUNC_bpf_per_cpu_ptr:
+ return &bpf_per_cpu_ptr_proto;
default:
return NULL;
}
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 1defa5f23078..feae87eaa8c6 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -3661,6 +3661,23 @@ union bpf_attr {
* *flags* are identical to those used for bpf_snprintf_btf.
* Return
* 0 on success or a negative error in case of failure.
+ *
+ * void *bpf_per_cpu_ptr(const void *percpu_ptr, u32 cpu)
+ * Description
+ * Take a pointer to a percpu ksym, *percpu_ptr*, and return a
+ * pointer to the percpu kernel variable on *cpu*. A ksym is an
+ * extern variable decorated with '__ksym'. For ksym, there is a
+ * global var (either static or global) defined of the same name
+ * in the kernel. The ksym is percpu if the global var is percpu.
+ * The returned pointer points to the global percpu var on *cpu*.
+ *
+ * bpf_per_cpu_ptr() has the same semantic as per_cpu_ptr() in the
+ * kernel, except that bpf_per_cpu_ptr() may return NULL. This
+ * happens if *cpu* is larger than nr_cpu_ids. The caller of
+ * bpf_per_cpu_ptr() must check the returned value.
+ * Return
+ * A pointer pointing to the kernel percpu variable on *cpu*, or
+ * NULL, if *cpu* is invalid.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -3814,6 +3831,7 @@ union bpf_attr {
FN(copy_from_user), \
FN(snprintf_btf), \
FN(seq_printf_btf), \
+ FN(bpf_per_cpu_ptr), \
/* */

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
--
2.28.0.709.gb0816b6eb0-goog