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Date: Thu, 26 May 2022 23:34:51 +0200
From: Lorenzo Bianconi <lorenzo@...nel.org>
To: bpf@...r.kernel.org
Cc: netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
andrii@...nel.org, davem@...emloft.net, kuba@...nel.org,
edumazet@...gle.com, pabeni@...hat.com, pablo@...filter.org,
fw@...len.de, netfilter-devel@...r.kernel.org,
lorenzo.bianconi@...hat.com, brouer@...hat.com, toke@...hat.com,
memxor@...il.com, yhs@...com
Subject: [PATCH v4 bpf-next 03/14] bpf: Support rdonly PTR_TO_BTF_ID for pointer to const return value
From: Kumar Kartikeya Dwivedi <memxor@...il.com>
Allow specifying MEM_RDONLY flag with PTR_TO_BTF_ID, which blocks write
access to object even for cases where it is permitted using a custom
btf_struct_access callback. This is currently set for return values from
kfunc where it points to const struct.
This is not to mean that helpers cannot modify such a 'pointer to const
struct', it's just that any write access that is usually permitted for
such pointers in a program won't be allowed for this instance.
For RET_PTR_TO_MEM_OR_BTF_ID, MEM_RDONLY was previously folded because
it didn't apply to PTR_TO_BTF_ID. Now, we check if variable is const
and mark the pointer to it as MEM_RDONLY.
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
---
include/linux/btf.h | 29 ++++++++++++++++++++++++
kernel/bpf/btf.c | 24 --------------------
kernel/bpf/verifier.c | 39 ++++++++++++++++++++++++--------
net/bpf/test_run.c | 15 ++++++++++--
net/netfilter/nf_conntrack_bpf.c | 4 ++--
5 files changed, 74 insertions(+), 37 deletions(-)
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 2611cea2c2b6..f8dc5f810b40 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -234,6 +234,11 @@ static inline bool btf_type_is_typedef(const struct btf_type *t)
return BTF_INFO_KIND(t->info) == BTF_KIND_TYPEDEF;
}
+static inline bool btf_type_is_const(const struct btf_type *t)
+{
+ return BTF_INFO_KIND(t->info) == BTF_KIND_CONST;
+}
+
static inline bool btf_type_is_func(const struct btf_type *t)
{
return BTF_INFO_KIND(t->info) == BTF_KIND_FUNC;
@@ -264,6 +269,30 @@ static inline bool btf_type_is_struct(const struct btf_type *t)
return kind == BTF_KIND_STRUCT || kind == BTF_KIND_UNION;
}
+static inline bool btf_type_is_modifier(const struct btf_type *t)
+{
+ /* Some of them is not strictly a C modifier
+ * but they are grouped into the same bucket
+ * for BTF concern:
+ * A type (t) that refers to another
+ * type through t->type AND its size cannot
+ * be determined without following the t->type.
+ *
+ * ptr does not fall into this bucket
+ * because its size is always sizeof(void *).
+ */
+ switch (BTF_INFO_KIND(t->info)) {
+ case BTF_KIND_TYPEDEF:
+ case BTF_KIND_VOLATILE:
+ case BTF_KIND_CONST:
+ case BTF_KIND_RESTRICT:
+ case BTF_KIND_TYPE_TAG:
+ return true;
+ }
+
+ return false;
+}
+
static inline u16 btf_type_vlen(const struct btf_type *t)
{
return BTF_INFO_VLEN(t->info);
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 9f8dec0ab924..bcdfb8ef0481 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -431,30 +431,6 @@ static int btf_resolve(struct btf_verifier_env *env,
static int btf_func_check(struct btf_verifier_env *env,
const struct btf_type *t);
-static bool btf_type_is_modifier(const struct btf_type *t)
-{
- /* Some of them is not strictly a C modifier
- * but they are grouped into the same bucket
- * for BTF concern:
- * A type (t) that refers to another
- * type through t->type AND its size cannot
- * be determined without following the t->type.
- *
- * ptr does not fall into this bucket
- * because its size is always sizeof(void *).
- */
- switch (BTF_INFO_KIND(t->info)) {
- case BTF_KIND_TYPEDEF:
- case BTF_KIND_VOLATILE:
- case BTF_KIND_CONST:
- case BTF_KIND_RESTRICT:
- case BTF_KIND_TYPE_TAG:
- return true;
- }
-
- return false;
-}
-
bool btf_type_is_void(const struct btf_type *t)
{
return t == &btf_void;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e0be76861736..27db2ef8a006 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4507,6 +4507,11 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env,
}
if (env->ops->btf_struct_access) {
+ if (atype != BPF_READ && reg->type & MEM_RDONLY) {
+ verbose(env, "pointer points to const object, only read is supported\n");
+ return -EACCES;
+ }
+
ret = env->ops->btf_struct_access(&env->log, reg->btf, t,
off, size, atype, &btf_id, &flag);
} else {
@@ -7316,9 +7321,15 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
regs[BPF_REG_0].mem_size = meta.mem_size;
} else if (base_type(ret_type) == RET_PTR_TO_MEM_OR_BTF_ID) {
const struct btf_type *t;
+ bool is_const = false;
mark_reg_known_zero(env, regs, BPF_REG_0);
- t = btf_type_skip_modifiers(meta.ret_btf, meta.ret_btf_id, NULL);
+ t = btf_type_by_id(meta.ret_btf, meta.ret_btf_id);
+ while (btf_type_is_modifier(t)) {
+ if (btf_type_is_const(t))
+ is_const = true;
+ t = btf_type_by_id(meta.ret_btf, t->type);
+ }
if (!btf_type_is_struct(t)) {
u32 tsize;
const struct btf_type *ret;
@@ -7335,12 +7346,12 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
regs[BPF_REG_0].type = PTR_TO_MEM | ret_flag;
regs[BPF_REG_0].mem_size = tsize;
} else {
- /* MEM_RDONLY may be carried from ret_flag, but it
- * doesn't apply on PTR_TO_BTF_ID. Fold it, otherwise
- * it will confuse the check of PTR_TO_BTF_ID in
- * check_mem_access().
+ /* MEM_RDONLY is carried from ret_flag. Fold it if the
+ * variable whose pointer is being returned is not
+ * const.
*/
- ret_flag &= ~MEM_RDONLY;
+ if (!is_const)
+ ret_flag &= ~MEM_RDONLY;
regs[BPF_REG_0].type = PTR_TO_BTF_ID | ret_flag;
regs[BPF_REG_0].btf = meta.ret_btf;
@@ -7535,8 +7546,17 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
mark_reg_unknown(env, regs, BPF_REG_0);
mark_btf_func_reg_size(env, BPF_REG_0, t->size);
} else if (btf_type_is_ptr(t)) {
- ptr_type = btf_type_skip_modifiers(desc_btf, t->type,
- &ptr_type_id);
+ bool is_const = false;
+
+ ptr_type_id = t->type;
+ ptr_type = btf_type_by_id(desc_btf, ptr_type_id);
+ while (btf_type_is_modifier(ptr_type)) {
+ if (btf_type_is_const(ptr_type))
+ is_const = true;
+ ptr_type_id = ptr_type->type;
+ ptr_type = btf_type_by_id(desc_btf, ptr_type_id);
+ }
+
if (!btf_type_is_struct(ptr_type)) {
ptr_type_name = btf_name_by_offset(desc_btf,
ptr_type->name_off);
@@ -7547,7 +7567,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
}
mark_reg_known_zero(env, regs, BPF_REG_0);
regs[BPF_REG_0].btf = desc_btf;
- regs[BPF_REG_0].type = PTR_TO_BTF_ID;
+ regs[BPF_REG_0].type = PTR_TO_BTF_ID | (is_const ? MEM_RDONLY : 0);
regs[BPF_REG_0].btf_id = ptr_type_id;
if (btf_kfunc_id_set_contains(desc_btf, resolve_prog_type(env->prog),
BTF_KFUNC_TYPE_RET_NULL, func_id)) {
@@ -13374,6 +13394,7 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
break;
case PTR_TO_BTF_ID:
case PTR_TO_BTF_ID | PTR_UNTRUSTED:
+ case PTR_TO_BTF_ID | MEM_RDONLY:
if (type == BPF_READ) {
insn->code = BPF_LDX | BPF_PROBE_MEM |
BPF_SIZE((insn)->code);
diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 4b796e0a9667..2f381cb4acfa 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -582,6 +582,12 @@ bpf_kfunc_call_test_acquire(unsigned long *scalar_ptr)
return &prog_test_struct;
}
+noinline const struct prog_test_ref_kfunc *
+bpf_kfunc_call_test_acquire_const(void)
+{
+ return bpf_kfunc_call_test_acquire(NULL);
+}
+
noinline struct prog_test_member *
bpf_kfunc_call_memb_acquire(void)
{
@@ -589,12 +595,14 @@ bpf_kfunc_call_memb_acquire(void)
return NULL;
}
-noinline void bpf_kfunc_call_test_release(struct prog_test_ref_kfunc *p)
+noinline void bpf_kfunc_call_test_release(const struct prog_test_ref_kfunc *p)
{
+ struct prog_test_ref_kfunc *pp = (void *)p;
+
if (!p)
return;
- refcount_dec(&p->cnt);
+ refcount_dec(&pp->cnt);
}
noinline void bpf_kfunc_call_memb_release(struct prog_test_member *p)
@@ -704,6 +712,7 @@ BTF_ID(func, bpf_kfunc_call_test1)
BTF_ID(func, bpf_kfunc_call_test2)
BTF_ID(func, bpf_kfunc_call_test3)
BTF_ID(func, bpf_kfunc_call_test_acquire)
+BTF_ID(func, bpf_kfunc_call_test_acquire_const)
BTF_ID(func, bpf_kfunc_call_memb_acquire)
BTF_ID(func, bpf_kfunc_call_test_release)
BTF_ID(func, bpf_kfunc_call_memb_release)
@@ -723,6 +732,7 @@ BTF_SET_END(test_sk_check_kfunc_ids)
BTF_SET_START(test_sk_acquire_kfunc_ids)
BTF_ID(func, bpf_kfunc_call_test_acquire)
+BTF_ID(func, bpf_kfunc_call_test_acquire_const)
BTF_ID(func, bpf_kfunc_call_memb_acquire)
BTF_ID(func, bpf_kfunc_call_test_kptr_get)
BTF_SET_END(test_sk_acquire_kfunc_ids)
@@ -735,6 +745,7 @@ BTF_SET_END(test_sk_release_kfunc_ids)
BTF_SET_START(test_sk_ret_null_kfunc_ids)
BTF_ID(func, bpf_kfunc_call_test_acquire)
+BTF_ID(func, bpf_kfunc_call_test_acquire_const)
BTF_ID(func, bpf_kfunc_call_memb_acquire)
BTF_ID(func, bpf_kfunc_call_test_kptr_get)
BTF_SET_END(test_sk_ret_null_kfunc_ids)
diff --git a/net/netfilter/nf_conntrack_bpf.c b/net/netfilter/nf_conntrack_bpf.c
index bc4d5cd63a94..85f142739a21 100644
--- a/net/netfilter/nf_conntrack_bpf.c
+++ b/net/netfilter/nf_conntrack_bpf.c
@@ -130,7 +130,7 @@ __diag_ignore_all("-Wmissing-prototypes",
* @opts__sz - Length of the bpf_ct_opts structure
* Must be NF_BPF_CT_OPTS_SZ (12)
*/
-struct nf_conn *
+const struct nf_conn *
bpf_xdp_ct_lookup(struct xdp_md *xdp_ctx, struct bpf_sock_tuple *bpf_tuple,
u32 tuple__sz, struct bpf_ct_opts *opts, u32 opts__sz)
{
@@ -173,7 +173,7 @@ bpf_xdp_ct_lookup(struct xdp_md *xdp_ctx, struct bpf_sock_tuple *bpf_tuple,
* @opts__sz - Length of the bpf_ct_opts structure
* Must be NF_BPF_CT_OPTS_SZ (12)
*/
-struct nf_conn *
+const struct nf_conn *
bpf_skb_ct_lookup(struct __sk_buff *skb_ctx, struct bpf_sock_tuple *bpf_tuple,
u32 tuple__sz, struct bpf_ct_opts *opts, u32 opts__sz)
{
--
2.35.3
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