When a kfunc is not returning a pointer to a struct but to a plain type,
we can consider it is a valid allocated memory assuming that:
- one of the arguments is either called rdonly_buf_size or
rdwr_buf_size
- and this argument is a const from the caller point of view
We can then use this parameter as the size of the allocated memory.
The memory is either read-only or read-write based on the name
of the size parameter.
Signed-off-by: Benjamin Tissoires <[email protected]>
---
changes in v6:
- code review from Kartikeya:
- remove comment change that had no reasons to be
- remove handling of PTR_TO_MEM with kfunc releases
- introduce struct bpf_kfunc_arg_meta
- do rdonly/rdwr_buf_size check in btf_check_kfunc_arg_match
- reverted most of the changes in verifier.c
- make sure kfunc acquire is using a struct pointer, not just a plain
pointer
- also forward ref_obj_id to PTR_TO_MEM in kfunc to not use after free
the allocated memory
changes in v5:
- updated PTR_TO_MEM comment in btf.c to match upstream
- make it read-only or read-write based on the name of size
new in v4
---
include/linux/bpf.h | 10 ++++++-
include/linux/btf.h | 12 ++++++++
kernel/bpf/btf.c | 67 ++++++++++++++++++++++++++++++++++++++++---
kernel/bpf/verifier.c | 49 +++++++++++++++++++++++--------
4 files changed, 121 insertions(+), 17 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 2b21f2a3452f..5b8eadb6e7bc 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1916,12 +1916,20 @@ int btf_distill_func_proto(struct bpf_verifier_log *log,
const char *func_name,
struct btf_func_model *m);
+struct bpf_kfunc_arg_meta {
+ u64 r0_size;
+ bool r0_rdonly;
+ int ref_obj_id;
+ bool multiple_ref_obj_id;
+};
+
struct bpf_reg_state;
int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
struct bpf_reg_state *regs);
int btf_check_kfunc_arg_match(struct bpf_verifier_env *env,
const struct btf *btf, u32 func_id,
- struct bpf_reg_state *regs);
+ struct bpf_reg_state *regs,
+ struct bpf_kfunc_arg_meta *meta);
int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
struct bpf_reg_state *reg);
int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *prog,
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 1bfed7fa0428..31da4273c2ec 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -420,4 +420,16 @@ static inline int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dt
}
#endif
+static inline bool btf_type_is_struct_ptr(struct btf *btf, const struct btf_type *t)
+{
+ /* t comes in already as a pointer */
+ t = btf_type_by_id(btf, t->type);
+
+ /* allow const */
+ if (BTF_INFO_KIND(t->info) == BTF_KIND_CONST)
+ t = btf_type_by_id(btf, t->type);
+
+ return btf_type_is_struct(t);
+}
+
#endif
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 4423045b8ff3..552d7bc05a0c 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6168,10 +6168,36 @@ static bool is_kfunc_arg_mem_size(const struct btf *btf,
return true;
}
+static bool btf_is_kfunc_arg_mem_size(const struct btf *btf,
+ const struct btf_param *arg,
+ const struct bpf_reg_state *reg,
+ const char *name)
+{
+ int len, target_len = strlen(name);
+ const struct btf_type *t;
+ const char *param_name;
+
+ t = btf_type_skip_modifiers(btf, arg->type, NULL);
+ if (!btf_type_is_scalar(t) || reg->type != SCALAR_VALUE)
+ return false;
+
+ param_name = btf_name_by_offset(btf, arg->name_off);
+ if (str_is_empty(param_name))
+ return false;
+ len = strlen(param_name);
+ if (len != target_len)
+ return false;
+ if (strncmp(param_name, name, target_len))
+ return false;
+
+ return true;
+}
+
static int btf_check_func_arg_match(struct bpf_verifier_env *env,
const struct btf *btf, u32 func_id,
struct bpf_reg_state *regs,
- bool ptr_to_mem_ok)
+ bool ptr_to_mem_ok,
+ struct bpf_kfunc_arg_meta *kfunc_meta)
{
enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
struct bpf_verifier_log *log = &env->log;
@@ -6225,6 +6251,30 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
t = btf_type_skip_modifiers(btf, args[i].type, NULL);
if (btf_type_is_scalar(t)) {
+ if (is_kfunc && kfunc_meta) {
+ bool is_buf_size = false;
+
+ /* check for any const scalar parameter of name "rdonly_buf_size"
+ * or "rdwr_buf_size"
+ */
+ if (btf_is_kfunc_arg_mem_size(btf, &args[i], reg,
+ "rdonly_buf_size")) {
+ kfunc_meta->r0_rdonly = true;
+ is_buf_size = true;
+ } else if (btf_is_kfunc_arg_mem_size(btf, &args[i], reg,
+ "rdwr_buf_size"))
+ is_buf_size = true;
+
+ if (is_buf_size) {
+ if (kfunc_meta->r0_size) {
+ bpf_log(log, "2 or more rdonly/rdwr_buf_size parameters for kfunc");
+ return -EINVAL;
+ }
+
+ kfunc_meta->r0_size = reg->var_off.value;
+ }
+ }
+
if (reg->type == SCALAR_VALUE)
continue;
bpf_log(log, "R%d is not a scalar\n", regno);
@@ -6246,6 +6296,14 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
if (ret < 0)
return ret;
+ /* kptr_get is only valid for kfunc */
+ if (kfunc_meta && reg->ref_obj_id) {
+ /* check for any one ref_obj_id to keep track of memory */
+ if (kfunc_meta->ref_obj_id)
+ kfunc_meta->multiple_ref_obj_id = true;
+ kfunc_meta->ref_obj_id = reg->ref_obj_id;
+ }
+
/* kptr_get is only true for kfunc */
if (i == 0 && kptr_get) {
struct bpf_map_value_off_desc *off_desc;
@@ -6441,7 +6499,7 @@ int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
return -EINVAL;
is_global = prog->aux->func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL;
- err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global);
+ err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global, NULL);
/* Compiler optimizations can remove arguments from static functions
* or mismatched type can be passed into a global function.
@@ -6454,9 +6512,10 @@ int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
int btf_check_kfunc_arg_match(struct bpf_verifier_env *env,
const struct btf *btf, u32 func_id,
- struct bpf_reg_state *regs)
+ struct bpf_reg_state *regs,
+ struct bpf_kfunc_arg_meta *meta)
{
- return btf_check_func_arg_match(env, btf, func_id, regs, true);
+ return btf_check_func_arg_match(env, btf, func_id, regs, true, meta);
}
/* Convert BTF of a function into bpf_reg_state if possible
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3adcc0d123af..77556132db15 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7561,6 +7561,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
{
const struct btf_type *t, *func, *func_proto, *ptr_type;
struct bpf_reg_state *regs = cur_regs(env);
+ struct bpf_kfunc_arg_meta meta = { 0 };
const char *func_name, *ptr_type_name;
u32 i, nargs, func_id, ptr_type_id;
int err, insn_idx = *insn_idx_p;
@@ -7592,7 +7593,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
BTF_KFUNC_TYPE_ACQUIRE, func_id);
/* Check the arguments */
- err = btf_check_kfunc_arg_match(env, desc_btf, func_id, regs);
+ err = btf_check_kfunc_arg_match(env, desc_btf, func_id, regs, &meta);
if (err < 0)
return err;
/* In case of release function, we get register number of refcounted
@@ -7613,7 +7614,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
/* Check return type */
t = btf_type_skip_modifiers(desc_btf, func_proto->type, NULL);
- if (acq && !btf_type_is_ptr(t)) {
+ if (acq && !btf_type_is_struct_ptr(desc_btf, t)) {
verbose(env, "acquire kernel function does not return PTR_TO_BTF_ID\n");
return -EINVAL;
}
@@ -7625,17 +7626,41 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
ptr_type = btf_type_skip_modifiers(desc_btf, t->type,
&ptr_type_id);
if (!btf_type_is_struct(ptr_type)) {
- ptr_type_name = btf_name_by_offset(desc_btf,
- ptr_type->name_off);
- verbose(env, "kernel function %s returns pointer type %s %s is not supported\n",
- func_name, btf_type_str(ptr_type),
- ptr_type_name);
- return -EINVAL;
+ if (!meta.r0_size) {
+ ptr_type_name = btf_name_by_offset(desc_btf,
+ ptr_type->name_off);
+ verbose(env,
+ "kernel function %s returns pointer type %s %s is not supported\n",
+ func_name,
+ btf_type_str(ptr_type),
+ ptr_type_name);
+ return -EINVAL;
+ }
+
+ if (meta.multiple_ref_obj_id) {
+ verbose(env,
+ "kernel function %s has multiple memory tracked objects\n",
+ func_name);
+ return -EINVAL;
+ }
+
+ mark_reg_known_zero(env, regs, BPF_REG_0);
+ regs[BPF_REG_0].type = PTR_TO_MEM;
+ regs[BPF_REG_0].mem_size = meta.r0_size;
+
+ if (meta.r0_rdonly)
+ regs[BPF_REG_0].type |= MEM_RDONLY;
+
+ /* Ensures we don't access the memory after a release_reference() */
+ if (meta.ref_obj_id)
+ regs[BPF_REG_0].ref_obj_id = meta.ref_obj_id;
+ } else {
+ 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].btf_id = ptr_type_id;
}
- 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].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)) {
regs[BPF_REG_0].type |= PTR_MAYBE_NULL;
--
2.36.1
On 7/12/22 7:58 AM, Benjamin Tissoires wrote:
> When a kfunc is not returning a pointer to a struct but to a plain type,
> we can consider it is a valid allocated memory assuming that:
> - one of the arguments is either called rdonly_buf_size or
> rdwr_buf_size
> - and this argument is a const from the caller point of view
>
> We can then use this parameter as the size of the allocated memory.
>
> The memory is either read-only or read-write based on the name
> of the size parameter.
If I understand correctly, this permits a kfunc like
int *kfunc(..., int rdonly_buf_size);
...
int *p = kfunc(..., 20);
so the 'p' points to a memory buffer with size 20.
This looks like a strange interface although probably there
is a valid reason for this as I didn't participated in
earlier discussions.
>
> Signed-off-by: Benjamin Tissoires <[email protected]>
>
> ---
>
> changes in v6:
> - code review from Kartikeya:
> - remove comment change that had no reasons to be
> - remove handling of PTR_TO_MEM with kfunc releases
> - introduce struct bpf_kfunc_arg_meta
> - do rdonly/rdwr_buf_size check in btf_check_kfunc_arg_match
> - reverted most of the changes in verifier.c
> - make sure kfunc acquire is using a struct pointer, not just a plain
> pointer
> - also forward ref_obj_id to PTR_TO_MEM in kfunc to not use after free
> the allocated memory
>
> changes in v5:
> - updated PTR_TO_MEM comment in btf.c to match upstream
> - make it read-only or read-write based on the name of size
>
> new in v4
> ---
> include/linux/bpf.h | 10 ++++++-
> include/linux/btf.h | 12 ++++++++
> kernel/bpf/btf.c | 67 ++++++++++++++++++++++++++++++++++++++++---
> kernel/bpf/verifier.c | 49 +++++++++++++++++++++++--------
> 4 files changed, 121 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 2b21f2a3452f..5b8eadb6e7bc 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1916,12 +1916,20 @@ int btf_distill_func_proto(struct bpf_verifier_log *log,
> const char *func_name,
> struct btf_func_model *m);
>
> +struct bpf_kfunc_arg_meta {
> + u64 r0_size;
> + bool r0_rdonly;
> + int ref_obj_id;
> + bool multiple_ref_obj_id;
> +};
> +
> struct bpf_reg_state;
> int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
> struct bpf_reg_state *regs);
> int btf_check_kfunc_arg_match(struct bpf_verifier_env *env,
> const struct btf *btf, u32 func_id,
> - struct bpf_reg_state *regs);
> + struct bpf_reg_state *regs,
> + struct bpf_kfunc_arg_meta *meta);
> int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
> struct bpf_reg_state *reg);
> int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *prog,
> diff --git a/include/linux/btf.h b/include/linux/btf.h
> index 1bfed7fa0428..31da4273c2ec 100644
> --- a/include/linux/btf.h
> +++ b/include/linux/btf.h
> @@ -420,4 +420,16 @@ static inline int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dt
> }
> #endif
>
> +static inline bool btf_type_is_struct_ptr(struct btf *btf, const struct btf_type *t)
> +{
> + /* t comes in already as a pointer */
> + t = btf_type_by_id(btf, t->type);
> +
> + /* allow const */
> + if (BTF_INFO_KIND(t->info) == BTF_KIND_CONST)
> + t = btf_type_by_id(btf, t->type);
> +
> + return btf_type_is_struct(t);
> +}
> +
> #endif
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 4423045b8ff3..552d7bc05a0c 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -6168,10 +6168,36 @@ static bool is_kfunc_arg_mem_size(const struct btf *btf,
> return true;
> }
>
> +static bool btf_is_kfunc_arg_mem_size(const struct btf *btf,
> + const struct btf_param *arg,
> + const struct bpf_reg_state *reg,
> + const char *name)
> +{
> + int len, target_len = strlen(name);
> + const struct btf_type *t;
> + const char *param_name;
> +
> + t = btf_type_skip_modifiers(btf, arg->type, NULL);
> + if (!btf_type_is_scalar(t) || reg->type != SCALAR_VALUE)
> + return false;
> +
> + param_name = btf_name_by_offset(btf, arg->name_off);
> + if (str_is_empty(param_name))
> + return false;
> + len = strlen(param_name);
> + if (len != target_len)
> + return false;
> + if (strncmp(param_name, name, target_len))
strcmp(param_name, name) is enough. len == target_len and both len and
target_len is computed from strlen(...).
> + return false;
> +
> + return true;
> +}
> +
> static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> const struct btf *btf, u32 func_id,
> struct bpf_reg_state *regs,
> - bool ptr_to_mem_ok)
> + bool ptr_to_mem_ok,
> + struct bpf_kfunc_arg_meta *kfunc_meta)
> {
> enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
> struct bpf_verifier_log *log = &env->log;
> @@ -6225,6 +6251,30 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
>
> t = btf_type_skip_modifiers(btf, args[i].type, NULL);
> if (btf_type_is_scalar(t)) {
> + if (is_kfunc && kfunc_meta) {
> + bool is_buf_size = false;
> +
> + /* check for any const scalar parameter of name "rdonly_buf_size"
> + * or "rdwr_buf_size"
> + */
> + if (btf_is_kfunc_arg_mem_size(btf, &args[i], reg,
> + "rdonly_buf_size")) {
> + kfunc_meta->r0_rdonly = true;
> + is_buf_size = true;
> + } else if (btf_is_kfunc_arg_mem_size(btf, &args[i], reg,
> + "rdwr_buf_size"))
> + is_buf_size = true;
> +
> + if (is_buf_size) {
> + if (kfunc_meta->r0_size) {
> + bpf_log(log, "2 or more rdonly/rdwr_buf_size parameters for kfunc");
> + return -EINVAL;
> + }
> +
> + kfunc_meta->r0_size = reg->var_off.value;
Did we check 'reg' is a constant somewhere?
> + }
> + }
> +
> if (reg->type == SCALAR_VALUE)
> continue;
> bpf_log(log, "R%d is not a scalar\n", regno);
> @@ -6246,6 +6296,14 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> if (ret < 0)
> return ret;
>
> + /* kptr_get is only valid for kfunc */
> + if (kfunc_meta && reg->ref_obj_id) {
> + /* check for any one ref_obj_id to keep track of memory */
> + if (kfunc_meta->ref_obj_id)
> + kfunc_meta->multiple_ref_obj_id = true;
> + kfunc_meta->ref_obj_id = reg->ref_obj_id;
> + }
> +
> /* kptr_get is only true for kfunc */
> if (i == 0 && kptr_get) {
> struct bpf_map_value_off_desc *off_desc;
> @@ -6441,7 +6499,7 @@ int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
> return -EINVAL;
>
> is_global = prog->aux->func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL;
> - err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global);
> + err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global, NULL);
>
> /* Compiler optimizations can remove arguments from static functions
> * or mismatched type can be passed into a global function.
[...]
On Tue, 12 Jul 2022 at 17:03, Benjamin Tissoires
<[email protected]> wrote:
>
> When a kfunc is not returning a pointer to a struct but to a plain type,
> we can consider it is a valid allocated memory assuming that:
> - one of the arguments is either called rdonly_buf_size or
> rdwr_buf_size
> - and this argument is a const from the caller point of view
>
> We can then use this parameter as the size of the allocated memory.
>
> The memory is either read-only or read-write based on the name
> of the size parameter.
>
> Signed-off-by: Benjamin Tissoires <[email protected]>
>
> ---
>
> changes in v6:
> - code review from Kartikeya:
> - remove comment change that had no reasons to be
> - remove handling of PTR_TO_MEM with kfunc releases
> - introduce struct bpf_kfunc_arg_meta
> - do rdonly/rdwr_buf_size check in btf_check_kfunc_arg_match
> - reverted most of the changes in verifier.c
> - make sure kfunc acquire is using a struct pointer, not just a plain
> pointer
> - also forward ref_obj_id to PTR_TO_MEM in kfunc to not use after free
> the allocated memory
>
> changes in v5:
> - updated PTR_TO_MEM comment in btf.c to match upstream
> - make it read-only or read-write based on the name of size
>
> new in v4
> ---
> include/linux/bpf.h | 10 ++++++-
> include/linux/btf.h | 12 ++++++++
> kernel/bpf/btf.c | 67 ++++++++++++++++++++++++++++++++++++++++---
> kernel/bpf/verifier.c | 49 +++++++++++++++++++++++--------
> 4 files changed, 121 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 2b21f2a3452f..5b8eadb6e7bc 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -1916,12 +1916,20 @@ int btf_distill_func_proto(struct bpf_verifier_log *log,
> const char *func_name,
> struct btf_func_model *m);
>
> +struct bpf_kfunc_arg_meta {
> + u64 r0_size;
> + bool r0_rdonly;
> + int ref_obj_id;
> + bool multiple_ref_obj_id;
> +};
> +
> struct bpf_reg_state;
> int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
> struct bpf_reg_state *regs);
> int btf_check_kfunc_arg_match(struct bpf_verifier_env *env,
> const struct btf *btf, u32 func_id,
> - struct bpf_reg_state *regs);
> + struct bpf_reg_state *regs,
> + struct bpf_kfunc_arg_meta *meta);
> int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
> struct bpf_reg_state *reg);
> int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *prog,
> diff --git a/include/linux/btf.h b/include/linux/btf.h
> index 1bfed7fa0428..31da4273c2ec 100644
> --- a/include/linux/btf.h
> +++ b/include/linux/btf.h
> @@ -420,4 +420,16 @@ static inline int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dt
> }
> #endif
>
> +static inline bool btf_type_is_struct_ptr(struct btf *btf, const struct btf_type *t)
> +{
> + /* t comes in already as a pointer */
> + t = btf_type_by_id(btf, t->type);
> +
> + /* allow const */
> + if (BTF_INFO_KIND(t->info) == BTF_KIND_CONST)
> + t = btf_type_by_id(btf, t->type);
Any specific reason to not allow any other modifiers apart from const?
volatile, restrict, typedef..?
If not, just use btf_type_skip_modifiers instead.
> +
> + return btf_type_is_struct(t);
> +}
> +
> #endif
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 4423045b8ff3..552d7bc05a0c 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -6168,10 +6168,36 @@ static bool is_kfunc_arg_mem_size(const struct btf *btf,
> return true;
> }
>
> +static bool btf_is_kfunc_arg_mem_size(const struct btf *btf,
> + const struct btf_param *arg,
> + const struct bpf_reg_state *reg,
> + const char *name)
It would be nicer if we could reuse some code from
is_kfunc_arg_mem_size, the only difference is matching suffix vs full
string. But don't feel too strongly about it.
> +{
> + int len, target_len = strlen(name);
> + const struct btf_type *t;
> + const char *param_name;
> +
> + t = btf_type_skip_modifiers(btf, arg->type, NULL);
> + if (!btf_type_is_scalar(t) || reg->type != SCALAR_VALUE)
> + return false;
> +
> + param_name = btf_name_by_offset(btf, arg->name_off);
> + if (str_is_empty(param_name))
> + return false;
> + len = strlen(param_name);
> + if (len != target_len)
> + return false;
> + if (strncmp(param_name, name, target_len))
> + return false;
> +
> + return true;
> +}
> +
> static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> const struct btf *btf, u32 func_id,
> struct bpf_reg_state *regs,
> - bool ptr_to_mem_ok)
> + bool ptr_to_mem_ok,
> + struct bpf_kfunc_arg_meta *kfunc_meta)
> {
> enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
> struct bpf_verifier_log *log = &env->log;
> @@ -6225,6 +6251,30 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
>
> t = btf_type_skip_modifiers(btf, args[i].type, NULL);
> if (btf_type_is_scalar(t)) {
> + if (is_kfunc && kfunc_meta) {
> + bool is_buf_size = false;
> +
> + /* check for any const scalar parameter of name "rdonly_buf_size"
> + * or "rdwr_buf_size"
> + */
> + if (btf_is_kfunc_arg_mem_size(btf, &args[i], reg,
> + "rdonly_buf_size")) {
> + kfunc_meta->r0_rdonly = true;
> + is_buf_size = true;
> + } else if (btf_is_kfunc_arg_mem_size(btf, &args[i], reg,
> + "rdwr_buf_size"))
> + is_buf_size = true;
> +
> + if (is_buf_size) {
> + if (kfunc_meta->r0_size) {
> + bpf_log(log, "2 or more rdonly/rdwr_buf_size parameters for kfunc");
> + return -EINVAL;
> + }
> +
> + kfunc_meta->r0_size = reg->var_off.value;
As Yonghong pointed out, you need to ensure the register holds a
constant value, by using tnum_is_const(reg->var_off), and giving an
error otherwise, because we need a constant size to be set for R0.
> + }
> + }
> +
> if (reg->type == SCALAR_VALUE)
> continue;
> bpf_log(log, "R%d is not a scalar\n", regno);
> @@ -6246,6 +6296,14 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> if (ret < 0)
> return ret;
>
> + /* kptr_get is only valid for kfunc */
Invalid comment
> + if (kfunc_meta && reg->ref_obj_id) {
> + /* check for any one ref_obj_id to keep track of memory */
> + if (kfunc_meta->ref_obj_id)
> + kfunc_meta->multiple_ref_obj_id = true;
Why not just return the error here itself? And then no need to keep
the multiple_ref_obj_id member.
When you return the error here, you can move a similar check in the if
(reg->type == PTR_TO_BTF_ID) block to this place so that we don't do
it twice.
> + kfunc_meta->ref_obj_id = reg->ref_obj_id;
> + }
> +
> /* kptr_get is only true for kfunc */
> if (i == 0 && kptr_get) {
> struct bpf_map_value_off_desc *off_desc;
> @@ -6441,7 +6499,7 @@ int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
> return -EINVAL;
>
> is_global = prog->aux->func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL;
> - err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global);
> + err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global, NULL);
>
> /* Compiler optimizations can remove arguments from static functions
> * or mismatched type can be passed into a global function.
> @@ -6454,9 +6512,10 @@ int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
>
> int btf_check_kfunc_arg_match(struct bpf_verifier_env *env,
> const struct btf *btf, u32 func_id,
> - struct bpf_reg_state *regs)
> + struct bpf_reg_state *regs,
> + struct bpf_kfunc_arg_meta *meta)
> {
> - return btf_check_func_arg_match(env, btf, func_id, regs, true);
> + return btf_check_func_arg_match(env, btf, func_id, regs, true, meta);
> }
>
> /* Convert BTF of a function into bpf_reg_state if possible
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 3adcc0d123af..77556132db15 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -7561,6 +7561,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> {
> const struct btf_type *t, *func, *func_proto, *ptr_type;
> struct bpf_reg_state *regs = cur_regs(env);
> + struct bpf_kfunc_arg_meta meta = { 0 };
> const char *func_name, *ptr_type_name;
> u32 i, nargs, func_id, ptr_type_id;
> int err, insn_idx = *insn_idx_p;
> @@ -7592,7 +7593,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> BTF_KFUNC_TYPE_ACQUIRE, func_id);
>
> /* Check the arguments */
> - err = btf_check_kfunc_arg_match(env, desc_btf, func_id, regs);
> + err = btf_check_kfunc_arg_match(env, desc_btf, func_id, regs, &meta);
> if (err < 0)
> return err;
> /* In case of release function, we get register number of refcounted
> @@ -7613,7 +7614,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> /* Check return type */
> t = btf_type_skip_modifiers(desc_btf, func_proto->type, NULL);
>
> - if (acq && !btf_type_is_ptr(t)) {
> + if (acq && !btf_type_is_struct_ptr(desc_btf, t)) {
> verbose(env, "acquire kernel function does not return PTR_TO_BTF_ID\n");
> return -EINVAL;
> }
> @@ -7625,17 +7626,41 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> ptr_type = btf_type_skip_modifiers(desc_btf, t->type,
> &ptr_type_id);
> if (!btf_type_is_struct(ptr_type)) {
> - ptr_type_name = btf_name_by_offset(desc_btf,
> - ptr_type->name_off);
> - verbose(env, "kernel function %s returns pointer type %s %s is not supported\n",
> - func_name, btf_type_str(ptr_type),
> - ptr_type_name);
> - return -EINVAL;
> + if (!meta.r0_size) {
> + ptr_type_name = btf_name_by_offset(desc_btf,
> + ptr_type->name_off);
> + verbose(env,
> + "kernel function %s returns pointer type %s %s is not supported\n",
> + func_name,
> + btf_type_str(ptr_type),
> + ptr_type_name);
> + return -EINVAL;
> + }
> +
> + if (meta.multiple_ref_obj_id) {
> + verbose(env,
> + "kernel function %s has multiple memory tracked objects\n",
> + func_name);
> + return -EINVAL;
> + }
> +
> + mark_reg_known_zero(env, regs, BPF_REG_0);
> + regs[BPF_REG_0].type = PTR_TO_MEM;
> + regs[BPF_REG_0].mem_size = meta.r0_size;
> +
> + if (meta.r0_rdonly)
> + regs[BPF_REG_0].type |= MEM_RDONLY;
> +
> + /* Ensures we don't access the memory after a release_reference() */
> + if (meta.ref_obj_id)
> + regs[BPF_REG_0].ref_obj_id = meta.ref_obj_id;
> + } else {
> + 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].btf_id = ptr_type_id;
> }
> - 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].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)) {
> regs[BPF_REG_0].type |= PTR_MAYBE_NULL;
> --
> 2.36.1
>
On Sat, Jul 16, 2022 at 6:29 AM Yonghong Song <[email protected]> wrote:
>
>
>
> On 7/12/22 7:58 AM, Benjamin Tissoires wrote:
> > When a kfunc is not returning a pointer to a struct but to a plain type,
> > we can consider it is a valid allocated memory assuming that:
> > - one of the arguments is either called rdonly_buf_size or
> > rdwr_buf_size
> > - and this argument is a const from the caller point of view
> >
> > We can then use this parameter as the size of the allocated memory.
> >
> > The memory is either read-only or read-write based on the name
> > of the size parameter.
>
> If I understand correctly, this permits a kfunc like
> int *kfunc(..., int rdonly_buf_size);
> ...
> int *p = kfunc(..., 20);
> so the 'p' points to a memory buffer with size 20.
Yes, exactly.
>
> This looks like a strange interface although probably there
> is a valid reason for this as I didn't participated in
> earlier discussions.
Well, the point is I need to be able to access a memory region that
was allocated dynamically. For drivers, the incoming data can not
usually be bound to a static value, and so we can not have the data
statically defined in the matching struct.
So this allows defining a kfunc to return any memory properly
allocated and owned by the device.
>
> >
> > Signed-off-by: Benjamin Tissoires <[email protected]>
> >
> > ---
> >
> > changes in v6:
> > - code review from Kartikeya:
> > - remove comment change that had no reasons to be
> > - remove handling of PTR_TO_MEM with kfunc releases
> > - introduce struct bpf_kfunc_arg_meta
> > - do rdonly/rdwr_buf_size check in btf_check_kfunc_arg_match
> > - reverted most of the changes in verifier.c
> > - make sure kfunc acquire is using a struct pointer, not just a plain
> > pointer
> > - also forward ref_obj_id to PTR_TO_MEM in kfunc to not use after free
> > the allocated memory
> >
> > changes in v5:
> > - updated PTR_TO_MEM comment in btf.c to match upstream
> > - make it read-only or read-write based on the name of size
> >
> > new in v4
> > ---
> > include/linux/bpf.h | 10 ++++++-
> > include/linux/btf.h | 12 ++++++++
> > kernel/bpf/btf.c | 67 ++++++++++++++++++++++++++++++++++++++++---
> > kernel/bpf/verifier.c | 49 +++++++++++++++++++++++--------
> > 4 files changed, 121 insertions(+), 17 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 2b21f2a3452f..5b8eadb6e7bc 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -1916,12 +1916,20 @@ int btf_distill_func_proto(struct bpf_verifier_log *log,
> > const char *func_name,
> > struct btf_func_model *m);
> >
> > +struct bpf_kfunc_arg_meta {
> > + u64 r0_size;
> > + bool r0_rdonly;
> > + int ref_obj_id;
> > + bool multiple_ref_obj_id;
> > +};
> > +
> > struct bpf_reg_state;
> > int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
> > struct bpf_reg_state *regs);
> > int btf_check_kfunc_arg_match(struct bpf_verifier_env *env,
> > const struct btf *btf, u32 func_id,
> > - struct bpf_reg_state *regs);
> > + struct bpf_reg_state *regs,
> > + struct bpf_kfunc_arg_meta *meta);
> > int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
> > struct bpf_reg_state *reg);
> > int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *prog,
> > diff --git a/include/linux/btf.h b/include/linux/btf.h
> > index 1bfed7fa0428..31da4273c2ec 100644
> > --- a/include/linux/btf.h
> > +++ b/include/linux/btf.h
> > @@ -420,4 +420,16 @@ static inline int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dt
> > }
> > #endif
> >
> > +static inline bool btf_type_is_struct_ptr(struct btf *btf, const struct btf_type *t)
> > +{
> > + /* t comes in already as a pointer */
> > + t = btf_type_by_id(btf, t->type);
> > +
> > + /* allow const */
> > + if (BTF_INFO_KIND(t->info) == BTF_KIND_CONST)
> > + t = btf_type_by_id(btf, t->type);
> > +
> > + return btf_type_is_struct(t);
> > +}
> > +
> > #endif
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index 4423045b8ff3..552d7bc05a0c 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -6168,10 +6168,36 @@ static bool is_kfunc_arg_mem_size(const struct btf *btf,
> > return true;
> > }
> >
> > +static bool btf_is_kfunc_arg_mem_size(const struct btf *btf,
> > + const struct btf_param *arg,
> > + const struct bpf_reg_state *reg,
> > + const char *name)
> > +{
> > + int len, target_len = strlen(name);
> > + const struct btf_type *t;
> > + const char *param_name;
> > +
> > + t = btf_type_skip_modifiers(btf, arg->type, NULL);
> > + if (!btf_type_is_scalar(t) || reg->type != SCALAR_VALUE)
> > + return false;
> > +
> > + param_name = btf_name_by_offset(btf, arg->name_off);
> > + if (str_is_empty(param_name))
> > + return false;
> > + len = strlen(param_name);
> > + if (len != target_len)
> > + return false;
> > + if (strncmp(param_name, name, target_len))
>
> strcmp(param_name, name) is enough. len == target_len and both len and
> target_len is computed from strlen(...).
Ack, fixed locally
>
> > + return false;
> > +
> > + return true;
> > +}
> > +
> > static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> > const struct btf *btf, u32 func_id,
> > struct bpf_reg_state *regs,
> > - bool ptr_to_mem_ok)
> > + bool ptr_to_mem_ok,
> > + struct bpf_kfunc_arg_meta *kfunc_meta)
> > {
> > enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
> > struct bpf_verifier_log *log = &env->log;
> > @@ -6225,6 +6251,30 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> >
> > t = btf_type_skip_modifiers(btf, args[i].type, NULL);
> > if (btf_type_is_scalar(t)) {
> > + if (is_kfunc && kfunc_meta) {
> > + bool is_buf_size = false;
> > +
> > + /* check for any const scalar parameter of name "rdonly_buf_size"
> > + * or "rdwr_buf_size"
> > + */
> > + if (btf_is_kfunc_arg_mem_size(btf, &args[i], reg,
> > + "rdonly_buf_size")) {
> > + kfunc_meta->r0_rdonly = true;
> > + is_buf_size = true;
> > + } else if (btf_is_kfunc_arg_mem_size(btf, &args[i], reg,
> > + "rdwr_buf_size"))
> > + is_buf_size = true;
> > +
> > + if (is_buf_size) {
> > + if (kfunc_meta->r0_size) {
> > + bpf_log(log, "2 or more rdonly/rdwr_buf_size parameters for kfunc");
> > + return -EINVAL;
> > + }
> > +
> > + kfunc_meta->r0_size = reg->var_off.value;
>
> Did we check 'reg' is a constant somewhere?
I used to check for it in the previous version, but I think it got
dropped in this revision. Re-adding this thanks to Kumar's help :)
Cheers,
Benjamin
>
> > + }
> > + }
> > +
> > if (reg->type == SCALAR_VALUE)
> > continue;
> > bpf_log(log, "R%d is not a scalar\n", regno);
> > @@ -6246,6 +6296,14 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> > if (ret < 0)
> > return ret;
> >
> > + /* kptr_get is only valid for kfunc */
> > + if (kfunc_meta && reg->ref_obj_id) {
> > + /* check for any one ref_obj_id to keep track of memory */
> > + if (kfunc_meta->ref_obj_id)
> > + kfunc_meta->multiple_ref_obj_id = true;
> > + kfunc_meta->ref_obj_id = reg->ref_obj_id;
> > + }
> > +
> > /* kptr_get is only true for kfunc */
> > if (i == 0 && kptr_get) {
> > struct bpf_map_value_off_desc *off_desc;
> > @@ -6441,7 +6499,7 @@ int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
> > return -EINVAL;
> >
> > is_global = prog->aux->func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL;
> > - err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global);
> > + err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global, NULL);
> >
> > /* Compiler optimizations can remove arguments from static functions
> > * or mismatched type can be passed into a global function.
> [...]
>
On Sat, Jul 16, 2022 at 10:33 PM Kumar Kartikeya Dwivedi
<[email protected]> wrote:
>
> On Tue, 12 Jul 2022 at 17:03, Benjamin Tissoires
> <[email protected]> wrote:
> >
> > When a kfunc is not returning a pointer to a struct but to a plain type,
> > we can consider it is a valid allocated memory assuming that:
> > - one of the arguments is either called rdonly_buf_size or
> > rdwr_buf_size
> > - and this argument is a const from the caller point of view
> >
> > We can then use this parameter as the size of the allocated memory.
> >
> > The memory is either read-only or read-write based on the name
> > of the size parameter.
> >
> > Signed-off-by: Benjamin Tissoires <[email protected]>
> >
> > ---
> >
> > changes in v6:
> > - code review from Kartikeya:
> > - remove comment change that had no reasons to be
> > - remove handling of PTR_TO_MEM with kfunc releases
> > - introduce struct bpf_kfunc_arg_meta
> > - do rdonly/rdwr_buf_size check in btf_check_kfunc_arg_match
> > - reverted most of the changes in verifier.c
> > - make sure kfunc acquire is using a struct pointer, not just a plain
> > pointer
> > - also forward ref_obj_id to PTR_TO_MEM in kfunc to not use after free
> > the allocated memory
> >
> > changes in v5:
> > - updated PTR_TO_MEM comment in btf.c to match upstream
> > - make it read-only or read-write based on the name of size
> >
> > new in v4
> > ---
> > include/linux/bpf.h | 10 ++++++-
> > include/linux/btf.h | 12 ++++++++
> > kernel/bpf/btf.c | 67 ++++++++++++++++++++++++++++++++++++++++---
> > kernel/bpf/verifier.c | 49 +++++++++++++++++++++++--------
> > 4 files changed, 121 insertions(+), 17 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 2b21f2a3452f..5b8eadb6e7bc 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -1916,12 +1916,20 @@ int btf_distill_func_proto(struct bpf_verifier_log *log,
> > const char *func_name,
> > struct btf_func_model *m);
> >
> > +struct bpf_kfunc_arg_meta {
> > + u64 r0_size;
> > + bool r0_rdonly;
> > + int ref_obj_id;
> > + bool multiple_ref_obj_id;
> > +};
> > +
> > struct bpf_reg_state;
> > int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
> > struct bpf_reg_state *regs);
> > int btf_check_kfunc_arg_match(struct bpf_verifier_env *env,
> > const struct btf *btf, u32 func_id,
> > - struct bpf_reg_state *regs);
> > + struct bpf_reg_state *regs,
> > + struct bpf_kfunc_arg_meta *meta);
> > int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog,
> > struct bpf_reg_state *reg);
> > int btf_check_type_match(struct bpf_verifier_log *log, const struct bpf_prog *prog,
> > diff --git a/include/linux/btf.h b/include/linux/btf.h
> > index 1bfed7fa0428..31da4273c2ec 100644
> > --- a/include/linux/btf.h
> > +++ b/include/linux/btf.h
> > @@ -420,4 +420,16 @@ static inline int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dt
> > }
> > #endif
> >
> > +static inline bool btf_type_is_struct_ptr(struct btf *btf, const struct btf_type *t)
> > +{
> > + /* t comes in already as a pointer */
> > + t = btf_type_by_id(btf, t->type);
> > +
> > + /* allow const */
> > + if (BTF_INFO_KIND(t->info) == BTF_KIND_CONST)
> > + t = btf_type_by_id(btf, t->type);
>
> Any specific reason to not allow any other modifiers apart from const?
> volatile, restrict, typedef..?
> If not, just use btf_type_skip_modifiers instead.
Good point. Fixed locally
>
> > +
> > + return btf_type_is_struct(t);
> > +}
> > +
> > #endif
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index 4423045b8ff3..552d7bc05a0c 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -6168,10 +6168,36 @@ static bool is_kfunc_arg_mem_size(const struct btf *btf,
> > return true;
> > }
> >
> > +static bool btf_is_kfunc_arg_mem_size(const struct btf *btf,
> > + const struct btf_param *arg,
> > + const struct bpf_reg_state *reg,
> > + const char *name)
>
> It would be nicer if we could reuse some code from
> is_kfunc_arg_mem_size, the only difference is matching suffix vs full
> string. But don't feel too strongly about it.
I'll see what I can do. There is indeed a lot of code duplication, but
I wasn't sure how I could express the differences while making it
obvious.
>
> > +{
> > + int len, target_len = strlen(name);
> > + const struct btf_type *t;
> > + const char *param_name;
> > +
> > + t = btf_type_skip_modifiers(btf, arg->type, NULL);
> > + if (!btf_type_is_scalar(t) || reg->type != SCALAR_VALUE)
> > + return false;
> > +
> > + param_name = btf_name_by_offset(btf, arg->name_off);
> > + if (str_is_empty(param_name))
> > + return false;
> > + len = strlen(param_name);
> > + if (len != target_len)
> > + return false;
> > + if (strncmp(param_name, name, target_len))
> > + return false;
> > +
> > + return true;
> > +}
> > +
> > static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> > const struct btf *btf, u32 func_id,
> > struct bpf_reg_state *regs,
> > - bool ptr_to_mem_ok)
> > + bool ptr_to_mem_ok,
> > + struct bpf_kfunc_arg_meta *kfunc_meta)
> > {
> > enum bpf_prog_type prog_type = resolve_prog_type(env->prog);
> > struct bpf_verifier_log *log = &env->log;
> > @@ -6225,6 +6251,30 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> >
> > t = btf_type_skip_modifiers(btf, args[i].type, NULL);
> > if (btf_type_is_scalar(t)) {
> > + if (is_kfunc && kfunc_meta) {
> > + bool is_buf_size = false;
> > +
> > + /* check for any const scalar parameter of name "rdonly_buf_size"
> > + * or "rdwr_buf_size"
> > + */
> > + if (btf_is_kfunc_arg_mem_size(btf, &args[i], reg,
> > + "rdonly_buf_size")) {
> > + kfunc_meta->r0_rdonly = true;
> > + is_buf_size = true;
> > + } else if (btf_is_kfunc_arg_mem_size(btf, &args[i], reg,
> > + "rdwr_buf_size"))
> > + is_buf_size = true;
> > +
> > + if (is_buf_size) {
> > + if (kfunc_meta->r0_size) {
> > + bpf_log(log, "2 or more rdonly/rdwr_buf_size parameters for kfunc");
> > + return -EINVAL;
> > + }
> > +
> > + kfunc_meta->r0_size = reg->var_off.value;
>
> As Yonghong pointed out, you need to ensure the register holds a
> constant value, by using tnum_is_const(reg->var_off), and giving an
> error otherwise, because we need a constant size to be set for R0.
Thanks for the hint on how to solve this. It saved me from doing
searches in the archives :)
As mentioned to Yonghong, I had it in a previous version, but the
refactoring dropped it :(
>
> > + }
> > + }
> > +
> > if (reg->type == SCALAR_VALUE)
> > continue;
> > bpf_log(log, "R%d is not a scalar\n", regno);
> > @@ -6246,6 +6296,14 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
> > if (ret < 0)
> > return ret;
> >
> > + /* kptr_get is only valid for kfunc */
>
> Invalid comment
oops
>
> > + if (kfunc_meta && reg->ref_obj_id) {
> > + /* check for any one ref_obj_id to keep track of memory */
> > + if (kfunc_meta->ref_obj_id)
> > + kfunc_meta->multiple_ref_obj_id = true;
>
> Why not just return the error here itself? And then no need to keep
> the multiple_ref_obj_id member.
> When you return the error here, you can move a similar check in the if
> (reg->type == PTR_TO_BTF_ID) block to this place so that we don't do
> it twice.
Good point. I extracted the block from (reg->type == PTR_TO_BTF_ID)
here, and at the end did a small "if (kfunc_meta && ref_obj_id)
kfunc_meta->ref_obj_id = ref_obj_id"
This way this path is done only once for all cases.
Cheers,
Benjamin
>
> > + kfunc_meta->ref_obj_id = reg->ref_obj_id;
> > + }
> > +
> > /* kptr_get is only true for kfunc */
> > if (i == 0 && kptr_get) {
> > struct bpf_map_value_off_desc *off_desc;
> > @@ -6441,7 +6499,7 @@ int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
> > return -EINVAL;
> >
> > is_global = prog->aux->func_info_aux[subprog].linkage == BTF_FUNC_GLOBAL;
> > - err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global);
> > + err = btf_check_func_arg_match(env, btf, btf_id, regs, is_global, NULL);
> >
> > /* Compiler optimizations can remove arguments from static functions
> > * or mismatched type can be passed into a global function.
> > @@ -6454,9 +6512,10 @@ int btf_check_subprog_arg_match(struct bpf_verifier_env *env, int subprog,
> >
> > int btf_check_kfunc_arg_match(struct bpf_verifier_env *env,
> > const struct btf *btf, u32 func_id,
> > - struct bpf_reg_state *regs)
> > + struct bpf_reg_state *regs,
> > + struct bpf_kfunc_arg_meta *meta)
> > {
> > - return btf_check_func_arg_match(env, btf, func_id, regs, true);
> > + return btf_check_func_arg_match(env, btf, func_id, regs, true, meta);
> > }
> >
> > /* Convert BTF of a function into bpf_reg_state if possible
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 3adcc0d123af..77556132db15 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -7561,6 +7561,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> > {
> > const struct btf_type *t, *func, *func_proto, *ptr_type;
> > struct bpf_reg_state *regs = cur_regs(env);
> > + struct bpf_kfunc_arg_meta meta = { 0 };
> > const char *func_name, *ptr_type_name;
> > u32 i, nargs, func_id, ptr_type_id;
> > int err, insn_idx = *insn_idx_p;
> > @@ -7592,7 +7593,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> > BTF_KFUNC_TYPE_ACQUIRE, func_id);
> >
> > /* Check the arguments */
> > - err = btf_check_kfunc_arg_match(env, desc_btf, func_id, regs);
> > + err = btf_check_kfunc_arg_match(env, desc_btf, func_id, regs, &meta);
> > if (err < 0)
> > return err;
> > /* In case of release function, we get register number of refcounted
> > @@ -7613,7 +7614,7 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> > /* Check return type */
> > t = btf_type_skip_modifiers(desc_btf, func_proto->type, NULL);
> >
> > - if (acq && !btf_type_is_ptr(t)) {
> > + if (acq && !btf_type_is_struct_ptr(desc_btf, t)) {
> > verbose(env, "acquire kernel function does not return PTR_TO_BTF_ID\n");
> > return -EINVAL;
> > }
> > @@ -7625,17 +7626,41 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
> > ptr_type = btf_type_skip_modifiers(desc_btf, t->type,
> > &ptr_type_id);
> > if (!btf_type_is_struct(ptr_type)) {
> > - ptr_type_name = btf_name_by_offset(desc_btf,
> > - ptr_type->name_off);
> > - verbose(env, "kernel function %s returns pointer type %s %s is not supported\n",
> > - func_name, btf_type_str(ptr_type),
> > - ptr_type_name);
> > - return -EINVAL;
> > + if (!meta.r0_size) {
> > + ptr_type_name = btf_name_by_offset(desc_btf,
> > + ptr_type->name_off);
> > + verbose(env,
> > + "kernel function %s returns pointer type %s %s is not supported\n",
> > + func_name,
> > + btf_type_str(ptr_type),
> > + ptr_type_name);
> > + return -EINVAL;
> > + }
> > +
> > + if (meta.multiple_ref_obj_id) {
> > + verbose(env,
> > + "kernel function %s has multiple memory tracked objects\n",
> > + func_name);
> > + return -EINVAL;
> > + }
> > +
> > + mark_reg_known_zero(env, regs, BPF_REG_0);
> > + regs[BPF_REG_0].type = PTR_TO_MEM;
> > + regs[BPF_REG_0].mem_size = meta.r0_size;
> > +
> > + if (meta.r0_rdonly)
> > + regs[BPF_REG_0].type |= MEM_RDONLY;
> > +
> > + /* Ensures we don't access the memory after a release_reference() */
> > + if (meta.ref_obj_id)
> > + regs[BPF_REG_0].ref_obj_id = meta.ref_obj_id;
> > + } else {
> > + 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].btf_id = ptr_type_id;
> > }
> > - 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].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)) {
> > regs[BPF_REG_0].type |= PTR_MAYBE_NULL;
> > --
> > 2.36.1
> >
>
On 7/18/22 7:36 AM, Benjamin Tissoires wrote:
> On Sat, Jul 16, 2022 at 6:29 AM Yonghong Song <[email protected]> wrote:
>>
>>
>>
>> On 7/12/22 7:58 AM, Benjamin Tissoires wrote:
>>> When a kfunc is not returning a pointer to a struct but to a plain type,
>>> we can consider it is a valid allocated memory assuming that:
>>> - one of the arguments is either called rdonly_buf_size or
>>> rdwr_buf_size
>>> - and this argument is a const from the caller point of view
>>>
>>> We can then use this parameter as the size of the allocated memory.
>>>
>>> The memory is either read-only or read-write based on the name
>>> of the size parameter.
>>
>> If I understand correctly, this permits a kfunc like
>> int *kfunc(..., int rdonly_buf_size);
>> ...
>> int *p = kfunc(..., 20);
>> so the 'p' points to a memory buffer with size 20.
>
> Yes, exactly.
>
>>
>> This looks like a strange interface although probably there
>> is a valid reason for this as I didn't participated in
>> earlier discussions.
>
> Well, the point is I need to be able to access a memory region that
> was allocated dynamically. For drivers, the incoming data can not
> usually be bound to a static value, and so we can not have the data
> statically defined in the matching struct.
> So this allows defining a kfunc to return any memory properly
> allocated and owned by the device.
Okay, thanks for explanation.
>
>>
>>>
>>> Signed-off-by: Benjamin Tissoires <[email protected]>
>>>
>>> ---
>>>
>>> changes in v6:
>>> - code review from Kartikeya:
>>> - remove comment change that had no reasons to be
>>> - remove handling of PTR_TO_MEM with kfunc releases
>>> - introduce struct bpf_kfunc_arg_meta
>>> - do rdonly/rdwr_buf_size check in btf_check_kfunc_arg_match
>>> - reverted most of the changes in verifier.c
>>> - make sure kfunc acquire is using a struct pointer, not just a plain
>>> pointer
>>> - also forward ref_obj_id to PTR_TO_MEM in kfunc to not use after free
>>> the allocated memory
>>>
>>> changes in v5:
>>> - updated PTR_TO_MEM comment in btf.c to match upstream
>>> - make it read-only or read-write based on the name of size
>>>
>>> new in v4
>>> ---
>>> include/linux/bpf.h | 10 ++++++-
>>> include/linux/btf.h | 12 ++++++++
>>> kernel/bpf/btf.c | 67 ++++++++++++++++++++++++++++++++++++++++---
>>> kernel/bpf/verifier.c | 49 +++++++++++++++++++++++--------
>>> 4 files changed, 121 insertions(+), 17 deletions(-)
>>>
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