From: Yonghong Song <yhs@fb.com>
Date: Thu, 27 Jan 2022 07:46:06 -0800
Subject: bpf: reject program if a __user tagged memory accessed in kernel way
Patch-mainline: v5.18-rc1
Git-commit: c6f1bfe89ac95dc829dcb4ed54780da134ac5fce
References: jsc#PED-1377
BPF verifier supports direct memory access for BPF_PROG_TYPE_TRACING type
of bpf programs, e.g., a->b. If "a" is a pointer
pointing to kernel memory, bpf verifier will allow user to write
code in C like a->b and the verifier will translate it to a kernel
load properly. If "a" is a pointer to user memory, it is expected
that bpf developer should be bpf_probe_read_user() helper to
get the value a->b. Without utilizing BTF __user tagging information,
current verifier will assume that a->b is a kernel memory access
and this may generate incorrect result.
Now BTF contains __user information, it can check whether the
pointer points to a user memory or not. If it is, the verifier
can reject the program and force users to use bpf_probe_read_user()
helper explicitly.
In the future, we can easily extend btf_add_space for other
address space tagging, for example, rcu/percpu etc.
Signed-off-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220127154606.654961-1-yhs@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
include/linux/bpf.h | 9 ++++++---
include/linux/btf.h | 5 +++++
kernel/bpf/btf.c | 34 ++++++++++++++++++++++++++++------
kernel/bpf/verifier.c | 35 ++++++++++++++++++++++++-----------
net/bpf/bpf_dummy_struct_ops.c | 6 ++++--
net/ipv4/bpf_tcp_ca.c | 6 ++++--
6 files changed, 71 insertions(+), 24 deletions(-)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -331,7 +331,10 @@ enum bpf_type_flag {
*/
MEM_ALLOC = BIT(2 + BPF_BASE_TYPE_BITS),
- __BPF_TYPE_LAST_FLAG = MEM_ALLOC,
+ /* MEM is in user address space. */
+ MEM_USER = BIT(3 + BPF_BASE_TYPE_BITS),
+
+ __BPF_TYPE_LAST_FLAG = MEM_USER,
};
/* Max number of base types. */
@@ -587,7 +590,7 @@ struct bpf_verifier_ops {
const struct btf *btf,
const struct btf_type *t, int off, int size,
enum bpf_access_type atype,
- u32 *next_btf_id);
+ u32 *next_btf_id, enum bpf_type_flag *flag);
};
struct bpf_prog_offload_ops {
@@ -1780,7 +1783,7 @@ static inline bool bpf_tracing_btf_ctx_a
int btf_struct_access(struct bpf_verifier_log *log, const struct btf *btf,
const struct btf_type *t, int off, int size,
enum bpf_access_type atype,
- u32 *next_btf_id);
+ u32 *next_btf_id, enum bpf_type_flag *flag);
bool btf_struct_ids_match(struct bpf_verifier_log *log,
const struct btf *btf, u32 id, int off,
const struct btf *need_btf, u32 need_type_id);
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -238,6 +238,11 @@ static inline bool btf_type_is_var(const
return BTF_INFO_KIND(t->info) == BTF_KIND_VAR;
}
+static inline bool btf_type_is_type_tag(const struct btf_type *t)
+{
+ return BTF_INFO_KIND(t->info) == BTF_KIND_TYPE_TAG;
+}
+
/* union is only a special case of struct:
* all its offsetof(member) == 0
*/
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -4886,6 +4886,7 @@ bool btf_ctx_access(int off, int size, e
const char *tname = prog->aux->attach_func_name;
struct bpf_verifier_log *log = info->log;
const struct btf_param *args;
+ const char *tag_value;
u32 nr_args, arg;
int i, ret;
@@ -5038,6 +5039,13 @@ bool btf_ctx_access(int off, int size, e
info->btf = btf;
info->btf_id = t->type;
t = btf_type_by_id(btf, t->type);
+
+ if (btf_type_is_type_tag(t)) {
+ tag_value = __btf_name_by_offset(btf, t->name_off);
+ if (strcmp(tag_value, "user") == 0)
+ info->reg_type |= MEM_USER;
+ }
+
/* skip modifiers */
while (btf_type_is_modifier(t)) {
info->btf_id = t->type;
@@ -5064,12 +5072,12 @@ enum bpf_struct_walk_result {
static int btf_struct_walk(struct bpf_verifier_log *log, const struct btf *btf,
const struct btf_type *t, int off, int size,
- u32 *next_btf_id)
+ u32 *next_btf_id, enum bpf_type_flag *flag)
{
u32 i, moff, mtrue_end, msize = 0, total_nelems = 0;
const struct btf_type *mtype, *elem_type = NULL;
const struct btf_member *member;
- const char *tname, *mname;
+ const char *tname, *mname, *tag_value;
u32 vlen, elem_id, mid;
again:
@@ -5253,7 +5261,8 @@ error:
}
if (btf_type_is_ptr(mtype)) {
- const struct btf_type *stype;
+ const struct btf_type *stype, *t;
+ enum bpf_type_flag tmp_flag = 0;
u32 id;
if (msize != size || off != moff) {
@@ -5262,9 +5271,19 @@ error:
mname, moff, tname, off, size);
return -EACCES;
}
+
+ /* check __user tag */
+ t = btf_type_by_id(btf, mtype->type);
+ if (btf_type_is_type_tag(t)) {
+ tag_value = __btf_name_by_offset(btf, t->name_off);
+ if (strcmp(tag_value, "user") == 0)
+ tmp_flag = MEM_USER;
+ }
+
stype = btf_type_skip_modifiers(btf, mtype->type, &id);
if (btf_type_is_struct(stype)) {
*next_btf_id = id;
+ *flag = tmp_flag;
return WALK_PTR;
}
}
@@ -5291,13 +5310,14 @@ error:
int btf_struct_access(struct bpf_verifier_log *log, const struct btf *btf,
const struct btf_type *t, int off, int size,
enum bpf_access_type atype __maybe_unused,
- u32 *next_btf_id)
+ u32 *next_btf_id, enum bpf_type_flag *flag)
{
+ enum bpf_type_flag tmp_flag = 0;
int err;
u32 id;
do {
- err = btf_struct_walk(log, btf, t, off, size, &id);
+ err = btf_struct_walk(log, btf, t, off, size, &id, &tmp_flag);
switch (err) {
case WALK_PTR:
@@ -5305,6 +5325,7 @@ int btf_struct_access(struct bpf_verifie
* we're done.
*/
*next_btf_id = id;
+ *flag = tmp_flag;
return PTR_TO_BTF_ID;
case WALK_SCALAR:
return SCALAR_VALUE;
@@ -5349,6 +5370,7 @@ bool btf_struct_ids_match(struct bpf_ver
const struct btf *need_btf, u32 need_type_id)
{
const struct btf_type *type;
+ enum bpf_type_flag flag;
int err;
/* Are we already done? */
@@ -5359,7 +5381,7 @@ again:
type = btf_type_by_id(btf, id);
if (!type)
return false;
- err = btf_struct_walk(log, btf, type, off, 1, &id);
+ err = btf_struct_walk(log, btf, type, off, 1, &id, &flag);
if (err != WALK_STRUCT)
return false;
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -536,7 +536,7 @@ static bool is_cmpxchg_insn(const struct
static const char *reg_type_str(struct bpf_verifier_env *env,
enum bpf_reg_type type)
{
- char postfix[16] = {0}, prefix[16] = {0};
+ char postfix[16] = {0}, prefix[32] = {0};
static const char * const str[] = {
[NOT_INIT] = "?",
[SCALAR_VALUE] = "inv",
@@ -570,9 +570,11 @@ static const char *reg_type_str(struct b
}
if (type & MEM_RDONLY)
- strncpy(prefix, "rdonly_", 16);
+ strncpy(prefix, "rdonly_", 32);
if (type & MEM_ALLOC)
- strncpy(prefix, "alloc_", 16);
+ strncpy(prefix, "alloc_", 32);
+ if (type & MEM_USER)
+ strncpy(prefix, "user_", 32);
snprintf(env->type_str_buf, TYPE_STR_BUF_LEN, "%s%s%s",
prefix, str[base_type(type)], postfix);
@@ -1547,14 +1549,15 @@ static void mark_reg_not_init(struct bpf
static void mark_btf_ld_reg(struct bpf_verifier_env *env,
struct bpf_reg_state *regs, u32 regno,
enum bpf_reg_type reg_type,
- struct btf *btf, u32 btf_id)
+ struct btf *btf, u32 btf_id,
+ enum bpf_type_flag flag)
{
if (reg_type == SCALAR_VALUE) {
mark_reg_unknown(env, regs, regno);
return;
}
mark_reg_known_zero(env, regs, regno);
- regs[regno].type = PTR_TO_BTF_ID;
+ regs[regno].type = PTR_TO_BTF_ID | flag;
regs[regno].btf = btf;
regs[regno].btf_id = btf_id;
}
@@ -4156,6 +4159,7 @@ static int check_ptr_to_btf_access(struc
struct bpf_reg_state *reg = regs + regno;
const struct btf_type *t = btf_type_by_id(reg->btf, reg->btf_id);
const char *tname = btf_name_by_offset(reg->btf, t->name_off);
+ enum bpf_type_flag flag = 0;
u32 btf_id;
int ret;
@@ -4175,9 +4179,16 @@ static int check_ptr_to_btf_access(struc
return -EACCES;
}
+ if (reg->type & MEM_USER) {
+ verbose(env,
+ "R%d is ptr_%s access user memory: off=%d\n",
+ regno, tname, off);
+ return -EACCES;
+ }
+
if (env->ops->btf_struct_access) {
ret = env->ops->btf_struct_access(&env->log, reg->btf, t,
- off, size, atype, &btf_id);
+ off, size, atype, &btf_id, &flag);
} else {
if (atype != BPF_READ) {
verbose(env, "only read is supported\n");
@@ -4185,14 +4196,14 @@ static int check_ptr_to_btf_access(struc
}
ret = btf_struct_access(&env->log, reg->btf, t, off, size,
- atype, &btf_id);
+ atype, &btf_id, &flag);
}
if (ret < 0)
return ret;
if (atype == BPF_READ && value_regno >= 0)
- mark_btf_ld_reg(env, regs, value_regno, ret, reg->btf, btf_id);
+ mark_btf_ld_reg(env, regs, value_regno, ret, reg->btf, btf_id, flag);
return 0;
}
@@ -4205,6 +4216,7 @@ static int check_ptr_to_map_access(struc
{
struct bpf_reg_state *reg = regs + regno;
struct bpf_map *map = reg->map_ptr;
+ enum bpf_type_flag flag = 0;
const struct btf_type *t;
const char *tname;
u32 btf_id;
@@ -4242,12 +4254,12 @@ static int check_ptr_to_map_access(struc
return -EACCES;
}
- ret = btf_struct_access(&env->log, btf_vmlinux, t, off, size, atype, &btf_id);
+ ret = btf_struct_access(&env->log, btf_vmlinux, t, off, size, atype, &btf_id, &flag);
if (ret < 0)
return ret;
if (value_regno >= 0)
- mark_btf_ld_reg(env, regs, value_regno, ret, btf_vmlinux, btf_id);
+ mark_btf_ld_reg(env, regs, value_regno, ret, btf_vmlinux, btf_id, flag);
return 0;
}
@@ -4448,7 +4460,8 @@ static int check_mem_access(struct bpf_v
if (err < 0)
return err;
- err = check_ctx_access(env, insn_idx, off, size, t, ®_type, &btf, &btf_id);
+ err = check_ctx_access(env, insn_idx, off, size, t, ®_type, &btf,
+ &btf_id);
if (err)
verbose_linfo(env, insn_idx, "; ");
if (!err && t == BPF_READ && value_regno >= 0) {
--- a/net/bpf/bpf_dummy_struct_ops.c
+++ b/net/bpf/bpf_dummy_struct_ops.c
@@ -145,7 +145,8 @@ static int bpf_dummy_ops_btf_struct_acce
const struct btf *btf,
const struct btf_type *t, int off,
int size, enum bpf_access_type atype,
- u32 *next_btf_id)
+ u32 *next_btf_id,
+ enum bpf_type_flag *flag)
{
const struct btf_type *state;
s32 type_id;
@@ -162,7 +163,8 @@ static int bpf_dummy_ops_btf_struct_acce
return -EACCES;
}
- err = btf_struct_access(log, btf, t, off, size, atype, next_btf_id);
+ err = btf_struct_access(log, btf, t, off, size, atype, next_btf_id,
+ flag);
if (err < 0)
return err;
--- a/net/ipv4/bpf_tcp_ca.c
+++ b/net/ipv4/bpf_tcp_ca.c
@@ -96,12 +96,14 @@ static int bpf_tcp_ca_btf_struct_access(
const struct btf *btf,
const struct btf_type *t, int off,
int size, enum bpf_access_type atype,
- u32 *next_btf_id)
+ u32 *next_btf_id,
+ enum bpf_type_flag *flag)
{
size_t end;
if (atype == BPF_READ)
- return btf_struct_access(log, btf, t, off, size, atype, next_btf_id);
+ return btf_struct_access(log, btf, t, off, size, atype, next_btf_id,
+ flag);
if (t != tcp_sock_type) {
bpf_log(log, "only read is supported\n");