Re: [PATCH bpf-next v5 2/6] bpf: Add a ARG_PTR_TO_CONST_STR argument type
On Tue, Apr 20, 2021 at 5:35 AM Florent Revest wrote:
>
> On Tue, Apr 20, 2021 at 12:54 AM Alexei Starovoitov
> wrote:
> >
> > On Mon, Apr 19, 2021 at 05:52:39PM +0200, Florent Revest wrote:
> > > This type provides the guarantee that an argument is going to be a const
> > > pointer to somewhere in a read-only map value. It also checks that this
> > > pointer is followed by a zero character before the end of the map value.
> > >
> > > Signed-off-by: Florent Revest
> > > Acked-by: Andrii Nakryiko
> > > ---
> > > include/linux/bpf.h | 1 +
> > > kernel/bpf/verifier.c | 41 +
> > > 2 files changed, 42 insertions(+)
> > >
> > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > > index 77d1d8c65b81..c160526fc8bf 100644
> > > --- a/include/linux/bpf.h
> > > +++ b/include/linux/bpf.h
> > > @@ -309,6 +309,7 @@ enum bpf_arg_type {
> > > ARG_PTR_TO_PERCPU_BTF_ID, /* pointer to in-kernel percpu type
> > > */
> > > ARG_PTR_TO_FUNC,/* pointer to a bpf program function */
> > > ARG_PTR_TO_STACK_OR_NULL, /* pointer to stack or NULL */
> > > + ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only
> > > string */
> > > __BPF_ARG_TYPE_MAX,
> > > };
> > >
> > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > > index 852541a435ef..5f46dd6f3383 100644
> > > --- a/kernel/bpf/verifier.c
> > > +++ b/kernel/bpf/verifier.c
> > > @@ -4787,6 +4787,7 @@ static const struct bpf_reg_types spin_lock_types =
> > > { .types = { PTR_TO_MAP_VALU
> > > static const struct bpf_reg_types percpu_btf_ptr_types = { .types = {
> > > PTR_TO_PERCPU_BTF_ID } };
> > > static const struct bpf_reg_types func_ptr_types = { .types = {
> > > PTR_TO_FUNC } };
> > > static const struct bpf_reg_types stack_ptr_types = { .types = {
> > > PTR_TO_STACK } };
> > > +static const struct bpf_reg_types const_str_ptr_types = { .types = {
> > > PTR_TO_MAP_VALUE } };
> > >
> > > static const struct bpf_reg_types
> > > *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
> > > [ARG_PTR_TO_MAP_KEY]= _key_value_types,
> > > @@ -4817,6 +4818,7 @@ static const struct bpf_reg_types
> > > *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
> > > [ARG_PTR_TO_PERCPU_BTF_ID] = _btf_ptr_types,
> > > [ARG_PTR_TO_FUNC] = _ptr_types,
> > > [ARG_PTR_TO_STACK_OR_NULL] = _ptr_types,
> > > + [ARG_PTR_TO_CONST_STR] = _str_ptr_types,
> > > };
> > >
> > > static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
> > > @@ -5067,6 +5069,45 @@ static int check_func_arg(struct bpf_verifier_env
> > > *env, u32 arg,
> > > if (err)
> > > return err;
> > > err = check_ptr_alignment(env, reg, 0, size, true);
> > > + } else if (arg_type == ARG_PTR_TO_CONST_STR) {
> > > + struct bpf_map *map = reg->map_ptr;
> > > + int map_off;
> > > + u64 map_addr;
> > > + char *str_ptr;
> > > +
> > > + if (reg->type != PTR_TO_MAP_VALUE || !map ||
> >
> > I think the 'type' check is redundant,
> > since check_reg_type() did it via compatible_reg_types.
> > If so it's probably better to remove it here ?
> >
> > '!map' looks unnecessary. Can it ever happen? If yes, it's a verifier bug.
> > For example in check_mem_access() we just deref reg->map_ptr without
> > checking
> > which, I think, is correct.
>
> I agree with all of the above. I only thought it's better to be safe
> than sorry but if you'd like I could follow up with a patch that
> removes some checks?
...
> Sure, does not hurt. I can also follow up with a patch unless if you
> prefer doing it yourself.
Please send a follow up patch.
I consider this kind of "safe than sorry" to be defensive programming that
promotes less-thinking-is-fine-because-its-faster-to-code style.
I'm sure you've seen my rants against defensive programming in the past :)
Re: [PATCH bpf-next v5 2/6] bpf: Add a ARG_PTR_TO_CONST_STR argument type
On Tue, Apr 20, 2021 at 12:54 AM Alexei Starovoitov
wrote:
>
> On Mon, Apr 19, 2021 at 05:52:39PM +0200, Florent Revest wrote:
> > This type provides the guarantee that an argument is going to be a const
> > pointer to somewhere in a read-only map value. It also checks that this
> > pointer is followed by a zero character before the end of the map value.
> >
> > Signed-off-by: Florent Revest
> > Acked-by: Andrii Nakryiko
> > ---
> > include/linux/bpf.h | 1 +
> > kernel/bpf/verifier.c | 41 +
> > 2 files changed, 42 insertions(+)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 77d1d8c65b81..c160526fc8bf 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -309,6 +309,7 @@ enum bpf_arg_type {
> > ARG_PTR_TO_PERCPU_BTF_ID, /* pointer to in-kernel percpu type */
> > ARG_PTR_TO_FUNC,/* pointer to a bpf program function */
> > ARG_PTR_TO_STACK_OR_NULL, /* pointer to stack or NULL */
> > + ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only
> > string */
> > __BPF_ARG_TYPE_MAX,
> > };
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 852541a435ef..5f46dd6f3383 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -4787,6 +4787,7 @@ static const struct bpf_reg_types spin_lock_types = {
> > .types = { PTR_TO_MAP_VALU
> > static const struct bpf_reg_types percpu_btf_ptr_types = { .types = {
> > PTR_TO_PERCPU_BTF_ID } };
> > static const struct bpf_reg_types func_ptr_types = { .types = {
> > PTR_TO_FUNC } };
> > static const struct bpf_reg_types stack_ptr_types = { .types = {
> > PTR_TO_STACK } };
> > +static const struct bpf_reg_types const_str_ptr_types = { .types = {
> > PTR_TO_MAP_VALUE } };
> >
> > static const struct bpf_reg_types
> > *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
> > [ARG_PTR_TO_MAP_KEY]= _key_value_types,
> > @@ -4817,6 +4818,7 @@ static const struct bpf_reg_types
> > *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
> > [ARG_PTR_TO_PERCPU_BTF_ID] = _btf_ptr_types,
> > [ARG_PTR_TO_FUNC] = _ptr_types,
> > [ARG_PTR_TO_STACK_OR_NULL] = _ptr_types,
> > + [ARG_PTR_TO_CONST_STR] = _str_ptr_types,
> > };
> >
> > static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
> > @@ -5067,6 +5069,45 @@ static int check_func_arg(struct bpf_verifier_env
> > *env, u32 arg,
> > if (err)
> > return err;
> > err = check_ptr_alignment(env, reg, 0, size, true);
> > + } else if (arg_type == ARG_PTR_TO_CONST_STR) {
> > + struct bpf_map *map = reg->map_ptr;
> > + int map_off;
> > + u64 map_addr;
> > + char *str_ptr;
> > +
> > + if (reg->type != PTR_TO_MAP_VALUE || !map ||
>
> I think the 'type' check is redundant,
> since check_reg_type() did it via compatible_reg_types.
> If so it's probably better to remove it here ?
>
> '!map' looks unnecessary. Can it ever happen? If yes, it's a verifier bug.
> For example in check_mem_access() we just deref reg->map_ptr without checking
> which, I think, is correct.
I agree with all of the above. I only thought it's better to be safe
than sorry but if you'd like I could follow up with a patch that
removes some checks?
> > + !bpf_map_is_rdonly(map)) {
>
> This check is needed, of course.
>
> > + verbose(env, "R%d does not point to a readonly
> > map'\n", regno);
> > + return -EACCES;
> > + }
> > +
> > + if (!tnum_is_const(reg->var_off)) {
> > + verbose(env, "R%d is not a constant address'\n",
> > regno);
> > + return -EACCES;
> > + }
> > +
> > + if (!map->ops->map_direct_value_addr) {
> > + verbose(env, "no direct value access support for this
> > map type\n");
> > + return -EACCES;
> > + }
> > +
> > + err = check_map_access(env, regno, reg->off,
> > +map->value_size - reg->off, false);
> > + if (err)
> > + return err;
> > +
> > + map_off = reg->off + reg->var_off.value;
> > + err = map->ops->map_direct_value_addr(map, _addr,
> > map_off);
> > + if (err) {
>
> since the code checks it here the same check in check_bpf_snprintf_call()
> should
> probably do:
> if (err) {
>verbose("verifier bug\n");
>return -EFAULT;
> }
>
> instead of just "return err;"
> ?
Sure, does not hurt. I can also follow up with a patch unless if you
prefer doing it yourself.
> > + verbose(env, "direct value access on string
> > failed\n");
>
> I think the message doesn't tell users much, but they probably should never
> see it unless they try to do lookup
Re: [PATCH bpf-next v5 2/6] bpf: Add a ARG_PTR_TO_CONST_STR argument type
On Mon, Apr 19, 2021 at 05:52:39PM +0200, Florent Revest wrote:
> This type provides the guarantee that an argument is going to be a const
> pointer to somewhere in a read-only map value. It also checks that this
> pointer is followed by a zero character before the end of the map value.
>
> Signed-off-by: Florent Revest
> Acked-by: Andrii Nakryiko
> ---
> include/linux/bpf.h | 1 +
> kernel/bpf/verifier.c | 41 +
> 2 files changed, 42 insertions(+)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 77d1d8c65b81..c160526fc8bf 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -309,6 +309,7 @@ enum bpf_arg_type {
> ARG_PTR_TO_PERCPU_BTF_ID, /* pointer to in-kernel percpu type */
> ARG_PTR_TO_FUNC,/* pointer to a bpf program function */
> ARG_PTR_TO_STACK_OR_NULL, /* pointer to stack or NULL */
> + ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only
> string */
> __BPF_ARG_TYPE_MAX,
> };
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 852541a435ef..5f46dd6f3383 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -4787,6 +4787,7 @@ static const struct bpf_reg_types spin_lock_types = {
> .types = { PTR_TO_MAP_VALU
> static const struct bpf_reg_types percpu_btf_ptr_types = { .types = {
> PTR_TO_PERCPU_BTF_ID } };
> static const struct bpf_reg_types func_ptr_types = { .types = { PTR_TO_FUNC
> } };
> static const struct bpf_reg_types stack_ptr_types = { .types = {
> PTR_TO_STACK } };
> +static const struct bpf_reg_types const_str_ptr_types = { .types = {
> PTR_TO_MAP_VALUE } };
>
> static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX]
> = {
> [ARG_PTR_TO_MAP_KEY]= _key_value_types,
> @@ -4817,6 +4818,7 @@ static const struct bpf_reg_types
> *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
> [ARG_PTR_TO_PERCPU_BTF_ID] = _btf_ptr_types,
> [ARG_PTR_TO_FUNC] = _ptr_types,
> [ARG_PTR_TO_STACK_OR_NULL] = _ptr_types,
> + [ARG_PTR_TO_CONST_STR] = _str_ptr_types,
> };
>
> static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
> @@ -5067,6 +5069,45 @@ static int check_func_arg(struct bpf_verifier_env
> *env, u32 arg,
> if (err)
> return err;
> err = check_ptr_alignment(env, reg, 0, size, true);
> + } else if (arg_type == ARG_PTR_TO_CONST_STR) {
> + struct bpf_map *map = reg->map_ptr;
> + int map_off;
> + u64 map_addr;
> + char *str_ptr;
> +
> + if (reg->type != PTR_TO_MAP_VALUE || !map ||
I think the 'type' check is redundant,
since check_reg_type() did it via compatible_reg_types.
If so it's probably better to remove it here ?
'!map' looks unnecessary. Can it ever happen? If yes, it's a verifier bug.
For example in check_mem_access() we just deref reg->map_ptr without checking
which, I think, is correct.
> + !bpf_map_is_rdonly(map)) {
This check is needed, of course.
> + verbose(env, "R%d does not point to a readonly map'\n",
> regno);
> + return -EACCES;
> + }
> +
> + if (!tnum_is_const(reg->var_off)) {
> + verbose(env, "R%d is not a constant address'\n", regno);
> + return -EACCES;
> + }
> +
> + if (!map->ops->map_direct_value_addr) {
> + verbose(env, "no direct value access support for this
> map type\n");
> + return -EACCES;
> + }
> +
> + err = check_map_access(env, regno, reg->off,
> +map->value_size - reg->off, false);
> + if (err)
> + return err;
> +
> + map_off = reg->off + reg->var_off.value;
> + err = map->ops->map_direct_value_addr(map, _addr, map_off);
> + if (err) {
since the code checks it here the same check in check_bpf_snprintf_call() should
probably do:
if (err) {
verbose("verifier bug\n");
return -EFAULT;
}
instead of just "return err;"
?
> + verbose(env, "direct value access on string failed\n");
I think the message doesn't tell users much, but they probably should never
see it unless they try to do lookup from readonly array with
more than one element.
So I guess it's fine to keep this one as-is. Just flagging.
Anyway the whole set looks great, so I've applied to bpf-next.
Thanks!
