* [PATCH bpf-next v1 1/3] bpf: add bpf_features enum
2025-06-25 0:05 [PATCH bpf-next v1 0/3] bpf: allow void* cast using bpf_rdonly_cast() Eduard Zingerman
@ 2025-06-25 0:05 ` Eduard Zingerman
2025-06-25 0:05 ` [PATCH bpf-next v1 2/3] bpf: allow void* cast using bpf_rdonly_cast() Eduard Zingerman
` (2 subsequent siblings)
3 siblings, 0 replies; 9+ messages in thread
From: Eduard Zingerman @ 2025-06-25 0:05 UTC (permalink / raw)
To: bpf, ast, andrii; +Cc: daniel, martin.lau, kernel-team, yonghong.song, eddyz87
This commit adds a kernel side enum for use in conjucntion with BTF
CO-RE bpf_core_enum_value_exists. The goal of the enum is to assist
with available BPF features detection. Intended usage looks as
follows:
if (bpf_core_enum_value_exists(enum bpf_features, BPF_FEAT_<f>))
... use feature f ...
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
kernel/bpf/verifier.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 279a64933262..71de4c9487d5 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -44,6 +44,10 @@ static const struct bpf_verifier_ops * const bpf_verifier_ops[] = {
#undef BPF_LINK_TYPE
};
+enum bpf_features {
+ __MAX_BPF_FEAT = 0,
+};
+
struct bpf_mem_alloc bpf_global_percpu_ma;
static bool bpf_global_percpu_ma_set;
@@ -24388,6 +24392,8 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr, __u3
u32 log_true_size;
bool is_priv;
+ BTF_TYPE_EMIT(enum bpf_features);
+
/* no program is valid */
if (ARRAY_SIZE(bpf_verifier_ops) == 0)
return -EINVAL;
--
2.47.1
^ permalink raw reply related [flat|nested] 9+ messages in thread* [PATCH bpf-next v1 2/3] bpf: allow void* cast using bpf_rdonly_cast()
2025-06-25 0:05 [PATCH bpf-next v1 0/3] bpf: allow void* cast using bpf_rdonly_cast() Eduard Zingerman
2025-06-25 0:05 ` [PATCH bpf-next v1 1/3] bpf: add bpf_features enum Eduard Zingerman
@ 2025-06-25 0:05 ` Eduard Zingerman
2025-06-25 0:11 ` Alexei Starovoitov
2025-06-25 0:05 ` [PATCH bpf-next v1 3/3] selftests/bpf: check operations on untrusted ro pointers to mem Eduard Zingerman
2025-06-25 0:07 ` [PATCH bpf-next v1 0/3] bpf: allow void* cast using bpf_rdonly_cast() Eduard Zingerman
3 siblings, 1 reply; 9+ messages in thread
From: Eduard Zingerman @ 2025-06-25 0:05 UTC (permalink / raw)
To: bpf, ast, andrii
Cc: daniel, martin.lau, kernel-team, yonghong.song, eddyz87,
Alexei Starovoitov, Andrii Nakryiko
Introduce support for `bpf_rdonly_cast(v, 0)`, which casts the value
`v` to an untyped, untrusted pointer, logically similar to a `void *`.
The memory pointed to by such a pointer is treated as read-only.
As with other untrusted pointers, memory access violations on loads
return zero instead of causing a fault.
Technically:
- The resulting pointer is represented as a register of type
`PTR_TO_MEM | MEM_RDONLY | PTR_UNTRUSTED` with size zero.
- Offsets within such pointers are not tracked.
- Same load instructions are allowed to have both
`PTR_TO_MEM | MEM_RDONLY | PTR_UNTRUSTED` and `PTR_TO_BTF_ID`
as the base pointer types.
In such cases, `bpf_insn_aux_data->ptr_type` is considered the
weaker of the two: `PTR_TO_MEM | MEM_RDONLY | PTR_UNTRUSTED`.
The following constraints apply to the new pointer type:
- can be used as a base for LDX instructions;
- can't be used as a base for ST/STX or atomic instructions;
- can't be used as parameter for kfuncs or helpers.
These constraints are enforced by existing handling of `MEM_RDONLY`
flag and `PTR_TO_MEM` of size zero.
Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Suggested-by: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
kernel/bpf/verifier.c | 75 +++++++++++++++++++++++++++++++++++--------
1 file changed, 62 insertions(+), 13 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 71de4c9487d5..6b2c38b7a7b6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -45,7 +45,8 @@ static const struct bpf_verifier_ops * const bpf_verifier_ops[] = {
};
enum bpf_features {
- __MAX_BPF_FEAT = 0,
+ BPF_FEAT_RDONLY_CAST_TO_VOID = 0,
+ __MAX_BPF_FEAT = 1,
};
struct bpf_mem_alloc bpf_global_percpu_ma;
@@ -7539,6 +7540,7 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
}
} else if (base_type(reg->type) == PTR_TO_MEM) {
bool rdonly_mem = type_is_rdonly_mem(reg->type);
+ bool rdonly_untrusted = rdonly_mem && (reg->type & PTR_UNTRUSTED);
if (type_may_be_null(reg->type)) {
verbose(env, "R%d invalid mem access '%s'\n", regno,
@@ -7558,8 +7560,13 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
return -EACCES;
}
- err = check_mem_region_access(env, regno, off, size,
- reg->mem_size, false);
+ /*
+ * Accesses to untrusted PTR_TO_MEM are done through probe
+ * instructions, hence no need to check bounds in that case.
+ */
+ if (!rdonly_untrusted)
+ err = check_mem_region_access(env, regno, off, size,
+ reg->mem_size, false);
if (!err && value_regno >= 0 && (t == BPF_READ || rdonly_mem))
mark_reg_unknown(env, regs, value_regno);
} else if (reg->type == PTR_TO_CTX) {
@@ -13606,16 +13613,24 @@ static int check_special_kfunc(struct bpf_verifier_env *env, struct bpf_kfunc_ca
regs[BPF_REG_0].btf_id = meta->ret_btf_id;
} else if (meta->func_id == special_kfunc_list[KF_bpf_rdonly_cast]) {
ret_t = btf_type_by_id(desc_btf, meta->arg_constant.value);
- if (!ret_t || !btf_type_is_struct(ret_t)) {
+ if (!ret_t) {
+ verbose(env, "Unknown type ID %lld passed to kfunc bpf_rdonly_cast\n",
+ meta->arg_constant.value);
+ return -EINVAL;
+ } else if (btf_type_is_struct(ret_t)) {
+ mark_reg_known_zero(env, regs, BPF_REG_0);
+ regs[BPF_REG_0].type = PTR_TO_BTF_ID | PTR_UNTRUSTED;
+ regs[BPF_REG_0].btf = desc_btf;
+ regs[BPF_REG_0].btf_id = meta->arg_constant.value;
+ } else if (btf_type_is_void(ret_t)) {
+ mark_reg_known_zero(env, regs, BPF_REG_0);
+ regs[BPF_REG_0].type = PTR_TO_MEM | MEM_RDONLY | PTR_UNTRUSTED;
+ regs[BPF_REG_0].mem_size = 0;
+ } else {
verbose(env,
- "kfunc bpf_rdonly_cast type ID argument must be of a struct\n");
+ "kfunc bpf_rdonly_cast type ID argument must be of a struct or void\n");
return -EINVAL;
}
-
- mark_reg_known_zero(env, regs, BPF_REG_0);
- regs[BPF_REG_0].type = PTR_TO_BTF_ID | PTR_UNTRUSTED;
- regs[BPF_REG_0].btf = desc_btf;
- regs[BPF_REG_0].btf_id = meta->arg_constant.value;
} else if (meta->func_id == special_kfunc_list[KF_bpf_dynptr_slice] ||
meta->func_id == special_kfunc_list[KF_bpf_dynptr_slice_rdwr]) {
enum bpf_type_flag type_flag = get_dynptr_type_flag(meta->initialized_dynptr.type);
@@ -14414,6 +14429,13 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env,
return -EACCES;
}
+ /*
+ * Accesses to untrusted PTR_TO_MEM are done through probe
+ * instructions, hence no need to track offsets.
+ */
+ if (base_type(ptr_reg->type) == PTR_TO_MEM && (ptr_reg->type & PTR_UNTRUSTED))
+ return 0;
+
switch (base_type(ptr_reg->type)) {
case PTR_TO_CTX:
case PTR_TO_MAP_VALUE:
@@ -19571,10 +19593,27 @@ static bool reg_type_mismatch(enum bpf_reg_type src, enum bpf_reg_type prev)
!reg_type_mismatch_ok(prev));
}
+static bool is_ptr_to_mem_or_btf_id(enum bpf_reg_type type)
+{
+ switch (base_type(type)) {
+ case PTR_TO_MEM:
+ case PTR_TO_BTF_ID:
+ return true;
+ default:
+ return false;
+ }
+}
+
+static bool is_ptr_to_mem(enum bpf_reg_type type)
+{
+ return base_type(type) == PTR_TO_MEM;
+}
+
static int save_aux_ptr_type(struct bpf_verifier_env *env, enum bpf_reg_type type,
bool allow_trust_mismatch)
{
enum bpf_reg_type *prev_type = &env->insn_aux_data[env->insn_idx].ptr_type;
+ enum bpf_reg_type merged_type;
if (*prev_type == NOT_INIT) {
/* Saw a valid insn
@@ -19591,15 +19630,24 @@ static int save_aux_ptr_type(struct bpf_verifier_env *env, enum bpf_reg_type typ
* Reject it.
*/
if (allow_trust_mismatch &&
- base_type(type) == PTR_TO_BTF_ID &&
- base_type(*prev_type) == PTR_TO_BTF_ID) {
+ is_ptr_to_mem_or_btf_id(type) &&
+ is_ptr_to_mem_or_btf_id(*prev_type)) {
/*
* Have to support a use case when one path through
* the program yields TRUSTED pointer while another
* is UNTRUSTED. Fallback to UNTRUSTED to generate
* BPF_PROBE_MEM/BPF_PROBE_MEMSX.
+ * Same behavior of MEM_RDONLY flag.
*/
- *prev_type = PTR_TO_BTF_ID | PTR_UNTRUSTED;
+ if (is_ptr_to_mem(type) || is_ptr_to_mem(*prev_type))
+ merged_type = PTR_TO_MEM;
+ else
+ merged_type = PTR_TO_BTF_ID;
+ if ((type & PTR_UNTRUSTED) || (*prev_type & PTR_UNTRUSTED))
+ merged_type |= PTR_UNTRUSTED;
+ if ((type & MEM_RDONLY) || (*prev_type & MEM_RDONLY))
+ merged_type |= MEM_RDONLY;
+ *prev_type = merged_type;
} else {
verbose(env, "same insn cannot be used with different pointers\n");
return -EINVAL;
@@ -21207,6 +21255,7 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
* for this case.
*/
case PTR_TO_BTF_ID | MEM_ALLOC | PTR_UNTRUSTED:
+ case PTR_TO_MEM | MEM_RDONLY | PTR_UNTRUSTED:
if (type == BPF_READ) {
if (BPF_MODE(insn->code) == BPF_MEM)
insn->code = BPF_LDX | BPF_PROBE_MEM |
--
2.47.1
^ permalink raw reply related [flat|nested] 9+ messages in thread* [PATCH bpf-next v1 3/3] selftests/bpf: check operations on untrusted ro pointers to mem
2025-06-25 0:05 [PATCH bpf-next v1 0/3] bpf: allow void* cast using bpf_rdonly_cast() Eduard Zingerman
2025-06-25 0:05 ` [PATCH bpf-next v1 1/3] bpf: add bpf_features enum Eduard Zingerman
2025-06-25 0:05 ` [PATCH bpf-next v1 2/3] bpf: allow void* cast using bpf_rdonly_cast() Eduard Zingerman
@ 2025-06-25 0:05 ` Eduard Zingerman
2025-06-25 0:07 ` [PATCH bpf-next v1 0/3] bpf: allow void* cast using bpf_rdonly_cast() Eduard Zingerman
3 siblings, 0 replies; 9+ messages in thread
From: Eduard Zingerman @ 2025-06-25 0:05 UTC (permalink / raw)
To: bpf, ast, andrii; +Cc: daniel, martin.lau, kernel-team, yonghong.song, eddyz87
The following cases are tested:
- it is ok to load memory at any offset from rdonly_untrusted_mem;
- rdonly_untrusted_mem offset/bounds are not tracked;
- writes into rdonly_untrusted_mem are forbidden;
- atomic operations on rdonly_untrusted_mem are forbidden;
- rdonly_untrusted_mem can't be passed as a memory argument of a
helper of kfunc;
- it is ok to use PTR_TO_MEM and PTR_TO_BTF_ID in a same load
instruction.
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
.../bpf/prog_tests/mem_rdonly_untrusted.c | 9 ++
.../bpf/progs/mem_rdonly_untrusted.c | 136 ++++++++++++++++++
2 files changed, 145 insertions(+)
create mode 100644 tools/testing/selftests/bpf/prog_tests/mem_rdonly_untrusted.c
create mode 100644 tools/testing/selftests/bpf/progs/mem_rdonly_untrusted.c
diff --git a/tools/testing/selftests/bpf/prog_tests/mem_rdonly_untrusted.c b/tools/testing/selftests/bpf/prog_tests/mem_rdonly_untrusted.c
new file mode 100644
index 000000000000..40d4f687bd9c
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/mem_rdonly_untrusted.c
@@ -0,0 +1,9 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <test_progs.h>
+#include "mem_rdonly_untrusted.skel.h"
+
+void test_mem_rdonly_untrusted(void)
+{
+ RUN_TESTS(mem_rdonly_untrusted);
+}
diff --git a/tools/testing/selftests/bpf/progs/mem_rdonly_untrusted.c b/tools/testing/selftests/bpf/progs/mem_rdonly_untrusted.c
new file mode 100644
index 000000000000..00604755e698
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/mem_rdonly_untrusted.c
@@ -0,0 +1,136 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include <bpf/bpf_core_read.h>
+#include "bpf_misc.h"
+#include "../test_kmods/bpf_testmod_kfunc.h"
+
+SEC("socket")
+__success
+__retval(0)
+int ldx_is_ok_bad_addr(void *ctx)
+{
+ char *p;
+
+ if (!bpf_core_enum_value_exists(enum bpf_features, BPF_FEAT_RDONLY_CAST_TO_VOID))
+ return 42;
+
+ p = bpf_rdonly_cast(0, 0);
+ return p[0x7fff];
+}
+
+SEC("socket")
+__success
+__retval(1)
+int ldx_is_ok_good_addr(void *ctx)
+{
+ int v, *p;
+
+ v = 1;
+ p = bpf_rdonly_cast(&v, 0);
+ return *p;
+}
+
+SEC("socket")
+__success
+int offset_not_tracked(void *ctx)
+{
+ int *p, i, s;
+
+ p = bpf_rdonly_cast(0, 0);
+ s = 0;
+ bpf_for(i, 0, 1000 * 1000 * 1000) {
+ p++;
+ s += *p;
+ }
+ return s;
+}
+
+SEC("socket")
+__failure
+__msg("cannot write into rdonly_untrusted_mem")
+int stx_not_ok(void *ctx)
+{
+ int v, *p;
+
+ v = 1;
+ p = bpf_rdonly_cast(&v, 0);
+ *p = 1;
+ return 0;
+}
+
+SEC("socket")
+__failure
+__msg("cannot write into rdonly_untrusted_mem")
+int atomic_not_ok(void *ctx)
+{
+ int v, *p;
+
+ v = 1;
+ p = bpf_rdonly_cast(&v, 0);
+ __sync_fetch_and_add(p, 1);
+ return 0;
+}
+
+SEC("socket")
+__failure
+__msg("cannot write into rdonly_untrusted_mem")
+int atomic_rmw_not_ok(void *ctx)
+{
+ long v, *p;
+
+ v = 1;
+ p = bpf_rdonly_cast(&v, 0);
+ return __sync_val_compare_and_swap(p, 0, 42);
+}
+
+SEC("socket")
+__failure
+__msg("invalid access to memory, mem_size=0 off=0 size=4")
+__msg("R1 min value is outside of the allowed memory range")
+int kfunc_param_not_ok(void *ctx)
+{
+ int *p;
+
+ p = bpf_rdonly_cast(0, 0);
+ bpf_kfunc_trusted_num_test(p);
+ return 0;
+}
+
+SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
+__failure
+__msg("R1 type=rdonly_untrusted_mem expected=")
+int helper_param_not_ok(void *ctx)
+{
+ char *p;
+
+ p = bpf_rdonly_cast(0, 0);
+ /*
+ * Any helper with ARG_CONST_SIZE_OR_ZERO constraint will do,
+ * the most permissive constraint
+ */
+ bpf_copy_from_user(p, 0, (void *)42);
+ return 0;
+}
+
+static __noinline u64 *get_some_addr(void)
+{
+ if (bpf_get_prandom_u32())
+ return bpf_rdonly_cast(0, bpf_core_type_id_kernel(struct sock));
+ else
+ return bpf_rdonly_cast(0, 0);
+}
+
+SEC("socket")
+__success
+__retval(0)
+int mixed_mem_type(void *ctx)
+{
+ u64 *p;
+
+ /* Try to avoid compiler hoisting load to if branches by using __noinline func. */
+ p = get_some_addr();
+ return *p;
+}
+
+char _license[] SEC("license") = "GPL";
--
2.47.1
^ permalink raw reply related [flat|nested] 9+ messages in thread