| Message ID | 20220306234311.452206-2-memxor@gmail.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | BPF |
| Headers | show |
| Series | Introduce bpf_packet_pointer helper | expand |
On Mon, Mar 7, 2022 at 1:24 AM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote: > > In the next patch, we will introduce a new helper 'bpf_packet_pointer' > that takes offset and len and returns a packet pointer. There we want to > statically enforce offset is in range [0, 0xffff], and that len is a > constant value, in range [1, 0xffff]. This also helps us avoid a > pointless runtime check. To make these checks possible, we need to > ensure we only get a scalar type. Although a lot of other argument types > take scalars, their intent is different. Hence add general ARG_SCALAR > and ARG_CONSTANT types, where the latter is also checked to be constant > in addition to being scalar. > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> > --- > include/linux/bpf.h | 2 ++ > kernel/bpf/verifier.c | 13 +++++++++++++ > 2 files changed, 15 insertions(+) > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index 88449fbbe063..7841d90b83df 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -391,6 +391,8 @@ enum bpf_arg_type { > ARG_PTR_TO_STACK, /* pointer to stack */ > ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only string */ > ARG_PTR_TO_TIMER, /* pointer to bpf_timer */ > + ARG_SCALAR, /* a scalar with any value(s) */ > + ARG_CONSTANT, /* a scalar with constant value */ > __BPF_ARG_TYPE_MAX, > Should we rename ARG_CONST_SIZE and ARG_CONST_SIZE_OR_ZERO to something like ARG_MEM_CONST_SIZE / ARG_MEM_CONST_SIZE_OR_ZERO to make the interface more explicit? I think that would make it less confusing to differentiate between ARG_CONST_SIZE and ARG_CONSTANT for arguments that describe the length/size but are not associated with a memory buffer. > /* Extended arg_types. */ > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index ec3a7b6c9515..0373d5bd240f 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -5163,6 +5163,12 @@ static bool arg_type_is_int_ptr(enum bpf_arg_type type) > type == ARG_PTR_TO_LONG; > } > > +static bool arg_type_is_scalar(enum bpf_arg_type type) > +{ > + return type == ARG_SCALAR || > + type == ARG_CONSTANT; > +} > + I think this function name might be a bit misleading since ARG_CONST_SIZE / ARG_CONST_SIZE_OR_ZERO / ARG_CONST_ALLOC_SIZE_OR_ZERO are also scalar arg types. Maybe one alternative is to add a function "arg_type_is_const" and then in check_func_arg, enforce that if arg_type_is_const, then tnum_is_const(reg->var_off) must be true. WDYT? > static int int_ptr_type_to_size(enum bpf_arg_type type) > { > if (type == ARG_PTR_TO_INT) > @@ -5302,6 +5308,8 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = { > [ARG_PTR_TO_STACK] = &stack_ptr_types, > [ARG_PTR_TO_CONST_STR] = &const_str_ptr_types, > [ARG_PTR_TO_TIMER] = &timer_types, > + [ARG_SCALAR] = &scalar_types, > + [ARG_CONSTANT] = &scalar_types, > }; > > static int check_reg_type(struct bpf_verifier_env *env, u32 regno, > @@ -5635,6 +5643,11 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg, > verbose(env, "string is not zero-terminated\n"); > return -EINVAL; > } > + } else if (arg_type_is_scalar(arg_type)) { > + if (arg_type == ARG_CONSTANT && !tnum_is_const(reg->var_off)) { > + verbose(env, "R%d is not a known constant\n", regno); > + return -EACCES; > + } > } > > return err; > -- > 2.35.1 >
On Tue, Mar 08, 2022 at 12:58:13AM IST, Joanne Koong wrote: > On Mon, Mar 7, 2022 at 1:24 AM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote: > > > > In the next patch, we will introduce a new helper 'bpf_packet_pointer' > > that takes offset and len and returns a packet pointer. There we want to > > statically enforce offset is in range [0, 0xffff], and that len is a > > constant value, in range [1, 0xffff]. This also helps us avoid a > > pointless runtime check. To make these checks possible, we need to > > ensure we only get a scalar type. Although a lot of other argument types > > take scalars, their intent is different. Hence add general ARG_SCALAR > > and ARG_CONSTANT types, where the latter is also checked to be constant > > in addition to being scalar. > > > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> > > --- > > include/linux/bpf.h | 2 ++ > > kernel/bpf/verifier.c | 13 +++++++++++++ > > 2 files changed, 15 insertions(+) > > > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > > index 88449fbbe063..7841d90b83df 100644 > > --- a/include/linux/bpf.h > > +++ b/include/linux/bpf.h > > @@ -391,6 +391,8 @@ enum bpf_arg_type { > > ARG_PTR_TO_STACK, /* pointer to stack */ > > ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only string */ > > ARG_PTR_TO_TIMER, /* pointer to bpf_timer */ > > + ARG_SCALAR, /* a scalar with any value(s) */ > > + ARG_CONSTANT, /* a scalar with constant value */ > > __BPF_ARG_TYPE_MAX, > > > > Should we rename ARG_CONST_SIZE and ARG_CONST_SIZE_OR_ZERO to > something like ARG_MEM_CONST_SIZE / ARG_MEM_CONST_SIZE_OR_ZERO to make > the interface more explicit? I think that would make it less confusing > to differentiate between ARG_CONST_SIZE and ARG_CONSTANT for arguments > that describe the length/size but are not associated with a memory > buffer. > I don't have a problem with that. I was just avoiding the churn since ARG_CONST_SIZE vs ARG_CONSTANT didn't seem confusing to me. > > > /* Extended arg_types. */ > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > index ec3a7b6c9515..0373d5bd240f 100644 > > --- a/kernel/bpf/verifier.c > > +++ b/kernel/bpf/verifier.c > > @@ -5163,6 +5163,12 @@ static bool arg_type_is_int_ptr(enum bpf_arg_type type) > > type == ARG_PTR_TO_LONG; > > } > > > > +static bool arg_type_is_scalar(enum bpf_arg_type type) > > +{ > > + return type == ARG_SCALAR || > > + type == ARG_CONSTANT; > > +} > > + > > I think this function name might be a bit misleading since > ARG_CONST_SIZE / ARG_CONST_SIZE_OR_ZERO / ARG_CONST_ALLOC_SIZE_OR_ZERO > are also scalar arg types. Maybe one alternative is to add a function They already have their own arg_type_is_mem_size, I think the naming here has no relation to the underlying compatible register types. ARG_CONSTANT is just a stronger ARG_SCALAR, so it makes sense to put both under arg_type_is_scalar umbrella. > "arg_type_is_const" and then in check_func_arg, enforce that if > arg_type_is_const, then tnum_is_const(reg->var_off) must be true. > WDYT? I don't think ARG_CONST_SIZE[_OR_ZERO] have any requirement that the scalar value must be a known constant, so tnum_is_const check would be prohibitive. I think the 'CONST' in their name is more misleading, so it might make sense to drop that instead. > > > static int int_ptr_type_to_size(enum bpf_arg_type type) > > { > > if (type == ARG_PTR_TO_INT) > > @@ -5302,6 +5308,8 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = { > > [ARG_PTR_TO_STACK] = &stack_ptr_types, > > [ARG_PTR_TO_CONST_STR] = &const_str_ptr_types, > > [ARG_PTR_TO_TIMER] = &timer_types, > > + [ARG_SCALAR] = &scalar_types, > > + [ARG_CONSTANT] = &scalar_types, > > }; > > > > static int check_reg_type(struct bpf_verifier_env *env, u32 regno, > > @@ -5635,6 +5643,11 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg, > > verbose(env, "string is not zero-terminated\n"); > > return -EINVAL; > > } > > + } else if (arg_type_is_scalar(arg_type)) { > > + if (arg_type == ARG_CONSTANT && !tnum_is_const(reg->var_off)) { > > + verbose(env, "R%d is not a known constant\n", regno); > > + return -EACCES; > > + } > > } > > > > return err; > > -- > > 2.35.1 > > -- Kartikeya
On Sun, Mar 6, 2022 at 3:43 PM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote: > > In the next patch, we will introduce a new helper 'bpf_packet_pointer' > that takes offset and len and returns a packet pointer. There we want to > statically enforce offset is in range [0, 0xffff], and that len is a > constant value, in range [1, 0xffff]. This also helps us avoid a > pointless runtime check. To make these checks possible, we need to > ensure we only get a scalar type. Although a lot of other argument types > take scalars, their intent is different. Hence add general ARG_SCALAR > and ARG_CONSTANT types, where the latter is also checked to be constant > in addition to being scalar. > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> > --- > include/linux/bpf.h | 2 ++ > kernel/bpf/verifier.c | 13 +++++++++++++ > 2 files changed, 15 insertions(+) > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index 88449fbbe063..7841d90b83df 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -391,6 +391,8 @@ enum bpf_arg_type { > ARG_PTR_TO_STACK, /* pointer to stack */ > ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only string */ > ARG_PTR_TO_TIMER, /* pointer to bpf_timer */ > + ARG_SCALAR, /* a scalar with any value(s) */ What's the difference between ARG_ANYTHING and ARG_SCALAR? > + ARG_CONSTANT, /* a scalar with constant value */ This ARG_CONSTANT serves a very similar purpose as ARG_CONST_ALLOC_SIZE_OR_ZERO, tbh. The only difference is that one is used to set meta->mem_size and this one is used (through extra func_id special handling) to set meta->ret_pkt_len. But meta->mem_size and meta->ret_pkt_len mean the same thing: how many bytes are directly accessible through a pointer returned from the helper. So I feel like there is some opportunity to unify and generalize, instead of adding more custom variants of constants. WDYT? > __BPF_ARG_TYPE_MAX, > > /* Extended arg_types. */ > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index ec3a7b6c9515..0373d5bd240f 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -5163,6 +5163,12 @@ static bool arg_type_is_int_ptr(enum bpf_arg_type type) > type == ARG_PTR_TO_LONG; > } > > +static bool arg_type_is_scalar(enum bpf_arg_type type) > +{ > + return type == ARG_SCALAR || > + type == ARG_CONSTANT; > +} > + > static int int_ptr_type_to_size(enum bpf_arg_type type) > { > if (type == ARG_PTR_TO_INT) > @@ -5302,6 +5308,8 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = { > [ARG_PTR_TO_STACK] = &stack_ptr_types, > [ARG_PTR_TO_CONST_STR] = &const_str_ptr_types, > [ARG_PTR_TO_TIMER] = &timer_types, > + [ARG_SCALAR] = &scalar_types, > + [ARG_CONSTANT] = &scalar_types, > }; > > static int check_reg_type(struct bpf_verifier_env *env, u32 regno, > @@ -5635,6 +5643,11 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg, > verbose(env, "string is not zero-terminated\n"); > return -EINVAL; > } > + } else if (arg_type_is_scalar(arg_type)) { > + if (arg_type == ARG_CONSTANT && !tnum_is_const(reg->var_off)) { > + verbose(env, "R%d is not a known constant\n", regno); > + return -EACCES; > + } > } > > return err; > -- > 2.35.1 >
On Tue, Mar 08, 2022 at 11:12:13AM IST, Andrii Nakryiko wrote: > On Sun, Mar 6, 2022 at 3:43 PM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote: > > > > In the next patch, we will introduce a new helper 'bpf_packet_pointer' > > that takes offset and len and returns a packet pointer. There we want to > > statically enforce offset is in range [0, 0xffff], and that len is a > > constant value, in range [1, 0xffff]. This also helps us avoid a > > pointless runtime check. To make these checks possible, we need to > > ensure we only get a scalar type. Although a lot of other argument types > > take scalars, their intent is different. Hence add general ARG_SCALAR > > and ARG_CONSTANT types, where the latter is also checked to be constant > > in addition to being scalar. > > > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> > > --- > > include/linux/bpf.h | 2 ++ > > kernel/bpf/verifier.c | 13 +++++++++++++ > > 2 files changed, 15 insertions(+) > > > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > > index 88449fbbe063..7841d90b83df 100644 > > --- a/include/linux/bpf.h > > +++ b/include/linux/bpf.h > > @@ -391,6 +391,8 @@ enum bpf_arg_type { > > ARG_PTR_TO_STACK, /* pointer to stack */ > > ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only string */ > > ARG_PTR_TO_TIMER, /* pointer to bpf_timer */ > > + ARG_SCALAR, /* a scalar with any value(s) */ > > What's the difference between ARG_ANYTHING and ARG_SCALAR? > ARG_SCALAR only accepts reg->type == SCALAR, ARG_ANYTHING accepts anything as long as reg->type != NOT_INIT (due to SRC_OP for check_reg_arg and early return without further checks). > > + ARG_CONSTANT, /* a scalar with constant value */ > > This ARG_CONSTANT serves a very similar purpose as > ARG_CONST_ALLOC_SIZE_OR_ZERO, tbh. The only difference is that one is > used to set meta->mem_size and this one is used (through extra func_id > special handling) to set meta->ret_pkt_len. But meta->mem_size and > meta->ret_pkt_len mean the same thing: how many bytes are directly > accessible through a pointer returned from the helper. So I feel like > there is some opportunity to unify and generalize, instead of adding > more custom variants of constants. WDYT? > I see, indeed it would make sense to make both equivalent, since CONST_ALLOC_SIZE must also be a constant. Joanne also mentioned consolidating, but I didn't understand how that would work for ARG_CONSTANT and ARG_CONST_SIZE ones. I'm wondering whether we can take a step back and should go with the following convention: ARG_MEM_SIZE, and two type flags, ARG_ZERO | ARG_CONSTANT Old New (in bpf_func_proto) ------------------------------------------------------------------- ARG_CONST_SIZE ARG_MEM_SIZE ARG_CONST_SIZE_OR_ZERO ARG_MEM_SIZE | ARG_ZERO ARG_CONST_ALLOC_SIZE ARG_MEM_SIZE | ARG_CONST ARG_CONST_ALLOC_SIZE_OR_ZERO ARG_MEM_SIZE | ARG_CONST | ARG_ZERO ARG_CONSTANT (mine) ARG_MEM_SIZE | ARG_CONST When we detect ARG_CONST, we always set meta->mem_size, which can be used to refine returned pointer range, otherwise meta->mem_size = -1 by default (so it will be -1 for the !tnum_is_const(reg->var_off) case). if (arg_type & ARG_CONST) meta->mem_size = reg->var_off.value; if (!(arg_type & ARG_ZERO) && !meta->mem_size) // error The check_mem_size_reg call is only made when we see that previous reg was ARG_PTR_TO_MEM. When preceding argument is not ARG_PTR_TO_MEM, we error if ARG_CONST is not set for ARG_MEM_SIZE (so that either the mem size is for previous parameter, or otherwise a constant size for the returned pointer). We can also only allow certain pointer return types for that case. If that is too much automagic, we can also discern using ARG_MEM_SIZE vs ARG_RET_MEM_SIZE, but I think the above is fine. ARG_CONST ofcourse only applies to args taking scalar type. > > > > __BPF_ARG_TYPE_MAX, > > > > /* Extended arg_types. */ > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > index ec3a7b6c9515..0373d5bd240f 100644 > > --- a/kernel/bpf/verifier.c > > +++ b/kernel/bpf/verifier.c > > @@ -5163,6 +5163,12 @@ static bool arg_type_is_int_ptr(enum bpf_arg_type type) > > type == ARG_PTR_TO_LONG; > > } > > > > +static bool arg_type_is_scalar(enum bpf_arg_type type) > > +{ > > + return type == ARG_SCALAR || > > + type == ARG_CONSTANT; > > +} > > + > > static int int_ptr_type_to_size(enum bpf_arg_type type) > > { > > if (type == ARG_PTR_TO_INT) > > @@ -5302,6 +5308,8 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = { > > [ARG_PTR_TO_STACK] = &stack_ptr_types, > > [ARG_PTR_TO_CONST_STR] = &const_str_ptr_types, > > [ARG_PTR_TO_TIMER] = &timer_types, > > + [ARG_SCALAR] = &scalar_types, > > + [ARG_CONSTANT] = &scalar_types, > > }; > > > > static int check_reg_type(struct bpf_verifier_env *env, u32 regno, > > @@ -5635,6 +5643,11 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg, > > verbose(env, "string is not zero-terminated\n"); > > return -EINVAL; > > } > > + } else if (arg_type_is_scalar(arg_type)) { > > + if (arg_type == ARG_CONSTANT && !tnum_is_const(reg->var_off)) { > > + verbose(env, "R%d is not a known constant\n", regno); > > + return -EACCES; > > + } > > } > > > > return err; > > -- > > 2.35.1 > > -- Kartikeya
On Mon, Mar 7, 2022 at 10:26 PM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote: > > On Tue, Mar 08, 2022 at 11:12:13AM IST, Andrii Nakryiko wrote: > > On Sun, Mar 6, 2022 at 3:43 PM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote: > > > > > > In the next patch, we will introduce a new helper 'bpf_packet_pointer' > > > that takes offset and len and returns a packet pointer. There we want to > > > statically enforce offset is in range [0, 0xffff], and that len is a > > > constant value, in range [1, 0xffff]. This also helps us avoid a > > > pointless runtime check. To make these checks possible, we need to > > > ensure we only get a scalar type. Although a lot of other argument types > > > take scalars, their intent is different. Hence add general ARG_SCALAR > > > and ARG_CONSTANT types, where the latter is also checked to be constant > > > in addition to being scalar. > > > > > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> > > > --- > > > include/linux/bpf.h | 2 ++ > > > kernel/bpf/verifier.c | 13 +++++++++++++ > > > 2 files changed, 15 insertions(+) > > > > > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > > > index 88449fbbe063..7841d90b83df 100644 > > > --- a/include/linux/bpf.h > > > +++ b/include/linux/bpf.h > > > @@ -391,6 +391,8 @@ enum bpf_arg_type { > > > ARG_PTR_TO_STACK, /* pointer to stack */ > > > ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only string */ > > > ARG_PTR_TO_TIMER, /* pointer to bpf_timer */ > > > + ARG_SCALAR, /* a scalar with any value(s) */ > > > > What's the difference between ARG_ANYTHING and ARG_SCALAR? > > > > ARG_SCALAR only accepts reg->type == SCALAR, ARG_ANYTHING accepts anything as > long as reg->type != NOT_INIT (due to SRC_OP for check_reg_arg and early return > without further checks). > Ah, ok, didn't realize that it's not always scalar for ARG_ANYTHING > > > + ARG_CONSTANT, /* a scalar with constant value */ > > > > This ARG_CONSTANT serves a very similar purpose as > > ARG_CONST_ALLOC_SIZE_OR_ZERO, tbh. The only difference is that one is > > used to set meta->mem_size and this one is used (through extra func_id > > special handling) to set meta->ret_pkt_len. But meta->mem_size and > > meta->ret_pkt_len mean the same thing: how many bytes are directly > > accessible through a pointer returned from the helper. So I feel like > > there is some opportunity to unify and generalize, instead of adding > > more custom variants of constants. WDYT? > > > > I see, indeed it would make sense to make both equivalent, since > CONST_ALLOC_SIZE must also be a constant. Joanne also mentioned consolidating, > but I didn't understand how that would work for ARG_CONSTANT and ARG_CONST_SIZE > ones. > > I'm wondering whether we can take a step back and should go with the following > convention: > > ARG_MEM_SIZE, and two type flags, ARG_ZERO | ARG_CONSTANT > > Old New (in bpf_func_proto) > ------------------------------------------------------------------- > ARG_CONST_SIZE ARG_MEM_SIZE > ARG_CONST_SIZE_OR_ZERO ARG_MEM_SIZE | ARG_ZERO > ARG_CONST_ALLOC_SIZE ARG_MEM_SIZE | ARG_CONST > ARG_CONST_ALLOC_SIZE_OR_ZERO ARG_MEM_SIZE | ARG_CONST | ARG_ZERO > ARG_CONSTANT (mine) ARG_MEM_SIZE | ARG_CONST > I think using "ARG_MEM_SIZE" as part of ARG_CONSTANT is backwards and misleading. It makes more sense to me to have ARG_CONSTANT and use ARG_ZERO (or rather ARG_MAYBE_ZERO?) and ARG_MEM_SIZE (to specify that this constant is describing the size of memory of a pointer that is passed in a previous argument). Basically, something like: ARG_CONST_SIZE => ARG_CONSTANT | ARG_MEM_SIZE ARG_CONST_SIZE_OR_ZERO => ARG_CONSTANT | ARG_MEM_SIZE | ARG_MAYBE_ZERO Then we can replace ARG_CONST_ALLOC_SIZE and ARG_CONST_ALLOC_SIZE_OR_ZERO with ARG_CONSTANT and ARG_CONSTANT | ARG_MAYBE_ZERO and we'll have a bit of special case to handle bpf_ringbuf_reserve. For ARG_CONSTANT, verifier will remember the value in bpf_call_arg_meta, and then we can use it as necessary (e.g., instead of mem_size when ARG_MEM_SIZE is specified) depending on context, helper being called, etc. Adding ARG_CONST just makes no sense as we always want constant value, otherwise it might as well be just ARG_ANYTHING, right? I haven't spent much time thinking about this, though, so I'm probably missing something. > When we detect ARG_CONST, we always set meta->mem_size, which can be used to > refine returned pointer range, otherwise meta->mem_size = -1 by default (so it > will be -1 for the !tnum_is_const(reg->var_off) case). > > if (arg_type & ARG_CONST) > meta->mem_size = reg->var_off.value; > if (!(arg_type & ARG_ZERO) && !meta->mem_size) > // error > > The check_mem_size_reg call is only made when we see that previous reg was > ARG_PTR_TO_MEM. When preceding argument is not ARG_PTR_TO_MEM, we error if > ARG_CONST is not set for ARG_MEM_SIZE (so that either the mem size is for > previous parameter, or otherwise a constant size for the returned pointer). > We can also only allow certain pointer return types for that case. > > If that is too much automagic, we can also discern using ARG_MEM_SIZE vs > ARG_RET_MEM_SIZE, but I think the above is fine. > > ARG_CONST ofcourse only applies to args taking scalar type. > > > > > > > > __BPF_ARG_TYPE_MAX, > > > > > > /* Extended arg_types. */ > > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > > index ec3a7b6c9515..0373d5bd240f 100644 > > > --- a/kernel/bpf/verifier.c > > > +++ b/kernel/bpf/verifier.c > > > @@ -5163,6 +5163,12 @@ static bool arg_type_is_int_ptr(enum bpf_arg_type type) > > > type == ARG_PTR_TO_LONG; > > > } > > > > > > +static bool arg_type_is_scalar(enum bpf_arg_type type) > > > +{ > > > + return type == ARG_SCALAR || > > > + type == ARG_CONSTANT; > > > +} > > > + > > > static int int_ptr_type_to_size(enum bpf_arg_type type) > > > { > > > if (type == ARG_PTR_TO_INT) > > > @@ -5302,6 +5308,8 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = { > > > [ARG_PTR_TO_STACK] = &stack_ptr_types, > > > [ARG_PTR_TO_CONST_STR] = &const_str_ptr_types, > > > [ARG_PTR_TO_TIMER] = &timer_types, > > > + [ARG_SCALAR] = &scalar_types, > > > + [ARG_CONSTANT] = &scalar_types, > > > }; > > > > > > static int check_reg_type(struct bpf_verifier_env *env, u32 regno, > > > @@ -5635,6 +5643,11 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg, > > > verbose(env, "string is not zero-terminated\n"); > > > return -EINVAL; > > > } > > > + } else if (arg_type_is_scalar(arg_type)) { > > > + if (arg_type == ARG_CONSTANT && !tnum_is_const(reg->var_off)) { > > > + verbose(env, "R%d is not a known constant\n", regno); > > > + return -EACCES; > > > + } > > > } > > > > > > return err; > > > -- > > > 2.35.1 > > > > > -- > Kartikeya
On Thu, Mar 10, 2022 at 3:05 PM Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote: > > On Mon, Mar 7, 2022 at 10:26 PM Kumar Kartikeya Dwivedi > <memxor@gmail.com> wrote: > > > > On Tue, Mar 08, 2022 at 11:12:13AM IST, Andrii Nakryiko wrote: > > > On Sun, Mar 6, 2022 at 3:43 PM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote: > > > > > > > > In the next patch, we will introduce a new helper 'bpf_packet_pointer' > > > > that takes offset and len and returns a packet pointer. There we want to > > > > statically enforce offset is in range [0, 0xffff], and that len is a > > > > constant value, in range [1, 0xffff]. This also helps us avoid a > > > > pointless runtime check. To make these checks possible, we need to > > > > ensure we only get a scalar type. Although a lot of other argument types > > > > take scalars, their intent is different. Hence add general ARG_SCALAR > > > > and ARG_CONSTANT types, where the latter is also checked to be constant > > > > in addition to being scalar. > > > > > > > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> > > > > --- > > > > include/linux/bpf.h | 2 ++ > > > > kernel/bpf/verifier.c | 13 +++++++++++++ > > > > 2 files changed, 15 insertions(+) > > > > > > > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > > > > index 88449fbbe063..7841d90b83df 100644 > > > > --- a/include/linux/bpf.h > > > > +++ b/include/linux/bpf.h > > > > @@ -391,6 +391,8 @@ enum bpf_arg_type { > > > > ARG_PTR_TO_STACK, /* pointer to stack */ > > > > ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only string */ > > > > ARG_PTR_TO_TIMER, /* pointer to bpf_timer */ > > > > + ARG_SCALAR, /* a scalar with any value(s) */ > > > > > > What's the difference between ARG_ANYTHING and ARG_SCALAR? > > > > > > > ARG_SCALAR only accepts reg->type == SCALAR, ARG_ANYTHING accepts anything as > > long as reg->type != NOT_INIT (due to SRC_OP for check_reg_arg and early return > > without further checks). > > > > Ah, ok, didn't realize that it's not always scalar for ARG_ANYTHING > > > > > > + ARG_CONSTANT, /* a scalar with constant value */ > > > > > > This ARG_CONSTANT serves a very similar purpose as > > > ARG_CONST_ALLOC_SIZE_OR_ZERO, tbh. The only difference is that one is > > > used to set meta->mem_size and this one is used (through extra func_id > > > special handling) to set meta->ret_pkt_len. But meta->mem_size and > > > meta->ret_pkt_len mean the same thing: how many bytes are directly > > > accessible through a pointer returned from the helper. So I feel like > > > there is some opportunity to unify and generalize, instead of adding > > > more custom variants of constants. WDYT? > > > > > > > I see, indeed it would make sense to make both equivalent, since > > CONST_ALLOC_SIZE must also be a constant. Joanne also mentioned consolidating, > > but I didn't understand how that would work for ARG_CONSTANT and ARG_CONST_SIZE > > ones. > > > > I'm wondering whether we can take a step back and should go with the following > > convention: > > > > ARG_MEM_SIZE, and two type flags, ARG_ZERO | ARG_CONSTANT > > > > Old New (in bpf_func_proto) > > ------------------------------------------------------------------- > > ARG_CONST_SIZE ARG_MEM_SIZE > > ARG_CONST_SIZE_OR_ZERO ARG_MEM_SIZE | ARG_ZERO > > ARG_CONST_ALLOC_SIZE ARG_MEM_SIZE | ARG_CONST > > ARG_CONST_ALLOC_SIZE_OR_ZERO ARG_MEM_SIZE | ARG_CONST | ARG_ZERO > > ARG_CONSTANT (mine) ARG_MEM_SIZE | ARG_CONST > > > > I think using "ARG_MEM_SIZE" as part of ARG_CONSTANT is backwards and > misleading. It makes more sense to me to have ARG_CONSTANT and use > ARG_ZERO (or rather ARG_MAYBE_ZERO?) and ARG_MEM_SIZE (to specify that > this constant is describing the size of memory of a pointer that is > passed in a previous argument). > > Basically, something like: > > ARG_CONST_SIZE => ARG_CONSTANT | ARG_MEM_SIZE > ARG_CONST_SIZE_OR_ZERO => ARG_CONSTANT | ARG_MEM_SIZE | ARG_MAYBE_ZERO > > Then we can replace ARG_CONST_ALLOC_SIZE and > ARG_CONST_ALLOC_SIZE_OR_ZERO with ARG_CONSTANT and ARG_CONSTANT | > ARG_MAYBE_ZERO and we'll have a bit of special case to handle > bpf_ringbuf_reserve. > > For ARG_CONSTANT, verifier will remember the value in > bpf_call_arg_meta, and then we can use it as necessary (e.g., instead > of mem_size when ARG_MEM_SIZE is specified) depending on context, > helper being called, etc. > > Adding ARG_CONST just makes no sense as we always want constant value, > otherwise it might as well be just ARG_ANYTHING, right? Re-reading this, this paragraph is very confusing (especially taking into account what I wrote above). My point was that in your table, you have ARG_MEM_SIZE as a "base type" and ARG_CONST as "modifier". And that makes little sense to me, because in all cases we have a constant, but not in all cases we use that constant to describe the size of memory passed in a previous argument. So I inverted that, ARG_CONSTANT as "base type", ARG_MEM_SIZE and ARG_MAYBE_ZERO as modifiers. And we then don't need 5 different resulting types because "CONST_ALLOC_SIZE" handling is just a custom constant handling for bpf_ringbuf_reserve. Just like for your use case you wanted to use plain ARG_CONSTANT and add some extra logic for your bpf_packet_pointer(). I hope this clarifies it a bit. > > I haven't spent much time thinking about this, though, so I'm probably > missing something. > > > > When we detect ARG_CONST, we always set meta->mem_size, which can be used to > > refine returned pointer range, otherwise meta->mem_size = -1 by default (so it > > will be -1 for the !tnum_is_const(reg->var_off) case). > > > > if (arg_type & ARG_CONST) > > meta->mem_size = reg->var_off.value; > > if (!(arg_type & ARG_ZERO) && !meta->mem_size) > > // error > > > > The check_mem_size_reg call is only made when we see that previous reg was > > ARG_PTR_TO_MEM. When preceding argument is not ARG_PTR_TO_MEM, we error if > > ARG_CONST is not set for ARG_MEM_SIZE (so that either the mem size is for > > previous parameter, or otherwise a constant size for the returned pointer). > > We can also only allow certain pointer return types for that case. > > > > If that is too much automagic, we can also discern using ARG_MEM_SIZE vs > > ARG_RET_MEM_SIZE, but I think the above is fine. > > > > ARG_CONST ofcourse only applies to args taking scalar type. > > > > > > > > > > > > __BPF_ARG_TYPE_MAX, > > > > > > > > /* Extended arg_types. */ > > > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > > > index ec3a7b6c9515..0373d5bd240f 100644 > > > > --- a/kernel/bpf/verifier.c > > > > +++ b/kernel/bpf/verifier.c > > > > @@ -5163,6 +5163,12 @@ static bool arg_type_is_int_ptr(enum bpf_arg_type type) > > > > type == ARG_PTR_TO_LONG; > > > > } > > > > > > > > +static bool arg_type_is_scalar(enum bpf_arg_type type) > > > > +{ > > > > + return type == ARG_SCALAR || > > > > + type == ARG_CONSTANT; > > > > +} > > > > + > > > > static int int_ptr_type_to_size(enum bpf_arg_type type) > > > > { > > > > if (type == ARG_PTR_TO_INT) > > > > @@ -5302,6 +5308,8 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = { > > > > [ARG_PTR_TO_STACK] = &stack_ptr_types, > > > > [ARG_PTR_TO_CONST_STR] = &const_str_ptr_types, > > > > [ARG_PTR_TO_TIMER] = &timer_types, > > > > + [ARG_SCALAR] = &scalar_types, > > > > + [ARG_CONSTANT] = &scalar_types, > > > > }; > > > > > > > > static int check_reg_type(struct bpf_verifier_env *env, u32 regno, > > > > @@ -5635,6 +5643,11 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg, > > > > verbose(env, "string is not zero-terminated\n"); > > > > return -EINVAL; > > > > } > > > > + } else if (arg_type_is_scalar(arg_type)) { > > > > + if (arg_type == ARG_CONSTANT && !tnum_is_const(reg->var_off)) { > > > > + verbose(env, "R%d is not a known constant\n", regno); > > > > + return -EACCES; > > > > + } > > > > } > > > > > > > > return err; > > > > -- > > > > 2.35.1 > > > > > > > > -- > > Kartikeya
On Fri, Mar 11, 2022 at 04:39:40AM IST, Andrii Nakryiko wrote: > On Thu, Mar 10, 2022 at 3:05 PM Andrii Nakryiko > <andrii.nakryiko@gmail.com> wrote: > > > > On Mon, Mar 7, 2022 at 10:26 PM Kumar Kartikeya Dwivedi > > <memxor@gmail.com> wrote: > > > > > > On Tue, Mar 08, 2022 at 11:12:13AM IST, Andrii Nakryiko wrote: > > > > On Sun, Mar 6, 2022 at 3:43 PM Kumar Kartikeya Dwivedi <memxor@gmail.com> wrote: > > > > > > > > > > In the next patch, we will introduce a new helper 'bpf_packet_pointer' > > > > > that takes offset and len and returns a packet pointer. There we want to > > > > > statically enforce offset is in range [0, 0xffff], and that len is a > > > > > constant value, in range [1, 0xffff]. This also helps us avoid a > > > > > pointless runtime check. To make these checks possible, we need to > > > > > ensure we only get a scalar type. Although a lot of other argument types > > > > > take scalars, their intent is different. Hence add general ARG_SCALAR > > > > > and ARG_CONSTANT types, where the latter is also checked to be constant > > > > > in addition to being scalar. > > > > > > > > > > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> > > > > > --- > > > > > include/linux/bpf.h | 2 ++ > > > > > kernel/bpf/verifier.c | 13 +++++++++++++ > > > > > 2 files changed, 15 insertions(+) > > > > > > > > > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > > > > > index 88449fbbe063..7841d90b83df 100644 > > > > > --- a/include/linux/bpf.h > > > > > +++ b/include/linux/bpf.h > > > > > @@ -391,6 +391,8 @@ enum bpf_arg_type { > > > > > ARG_PTR_TO_STACK, /* pointer to stack */ > > > > > ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only string */ > > > > > ARG_PTR_TO_TIMER, /* pointer to bpf_timer */ > > > > > + ARG_SCALAR, /* a scalar with any value(s) */ > > > > > > > > What's the difference between ARG_ANYTHING and ARG_SCALAR? > > > > > > > > > > ARG_SCALAR only accepts reg->type == SCALAR, ARG_ANYTHING accepts anything as > > > long as reg->type != NOT_INIT (due to SRC_OP for check_reg_arg and early return > > > without further checks). > > > > > > > Ah, ok, didn't realize that it's not always scalar for ARG_ANYTHING > > > > > > > > > + ARG_CONSTANT, /* a scalar with constant value */ > > > > > > > > This ARG_CONSTANT serves a very similar purpose as > > > > ARG_CONST_ALLOC_SIZE_OR_ZERO, tbh. The only difference is that one is > > > > used to set meta->mem_size and this one is used (through extra func_id > > > > special handling) to set meta->ret_pkt_len. But meta->mem_size and > > > > meta->ret_pkt_len mean the same thing: how many bytes are directly > > > > accessible through a pointer returned from the helper. So I feel like > > > > there is some opportunity to unify and generalize, instead of adding > > > > more custom variants of constants. WDYT? > > > > > > > > > > I see, indeed it would make sense to make both equivalent, since > > > CONST_ALLOC_SIZE must also be a constant. Joanne also mentioned consolidating, > > > but I didn't understand how that would work for ARG_CONSTANT and ARG_CONST_SIZE > > > ones. > > > > > > I'm wondering whether we can take a step back and should go with the following > > > convention: > > > > > > ARG_MEM_SIZE, and two type flags, ARG_ZERO | ARG_CONSTANT > > > > > > Old New (in bpf_func_proto) > > > ------------------------------------------------------------------- > > > ARG_CONST_SIZE ARG_MEM_SIZE > > > ARG_CONST_SIZE_OR_ZERO ARG_MEM_SIZE | ARG_ZERO > > > ARG_CONST_ALLOC_SIZE ARG_MEM_SIZE | ARG_CONST > > > ARG_CONST_ALLOC_SIZE_OR_ZERO ARG_MEM_SIZE | ARG_CONST | ARG_ZERO > > > ARG_CONSTANT (mine) ARG_MEM_SIZE | ARG_CONST > > > > > > > I think using "ARG_MEM_SIZE" as part of ARG_CONSTANT is backwards and > > misleading. It makes more sense to me to have ARG_CONSTANT and use > > ARG_ZERO (or rather ARG_MAYBE_ZERO?) and ARG_MEM_SIZE (to specify that > > this constant is describing the size of memory of a pointer that is > > passed in a previous argument). > > > > Basically, something like: > > > > ARG_CONST_SIZE => ARG_CONSTANT | ARG_MEM_SIZE > > ARG_CONST_SIZE_OR_ZERO => ARG_CONSTANT | ARG_MEM_SIZE | ARG_MAYBE_ZERO > > > > Then we can replace ARG_CONST_ALLOC_SIZE and > > ARG_CONST_ALLOC_SIZE_OR_ZERO with ARG_CONSTANT and ARG_CONSTANT | > > ARG_MAYBE_ZERO and we'll have a bit of special case to handle > > bpf_ringbuf_reserve. > > > > For ARG_CONSTANT, verifier will remember the value in > > bpf_call_arg_meta, and then we can use it as necessary (e.g., instead > > of mem_size when ARG_MEM_SIZE is specified) depending on context, > > helper being called, etc. > > > > Adding ARG_CONST just makes no sense as we always want constant value, > > otherwise it might as well be just ARG_ANYTHING, right? > > Re-reading this, this paragraph is very confusing (especially taking > into account what I wrote above). My point was that in your table, you > have ARG_MEM_SIZE as a "base type" and ARG_CONST as "modifier". And > that makes little sense to me, because in all cases we have a > constant, but not in all cases we use that constant to describe the > size of memory passed in a previous argument. So I inverted that, > ARG_CONSTANT as "base type", ARG_MEM_SIZE and ARG_MAYBE_ZERO as > modifiers. And we then don't need 5 different resulting types because > "CONST_ALLOC_SIZE" handling is just a custom constant handling for > bpf_ringbuf_reserve. Just like for your use case you wanted to use > plain ARG_CONSTANT and add some extra logic for your > bpf_packet_pointer(). I hope this clarifies it a bit. > Makes sense, I'll split it out as a separate change. Thanks! > > > > I haven't spent much time thinking about this, though, so I'm probably > > missing something. > > > > > > > When we detect ARG_CONST, we always set meta->mem_size, which can be used to > > > refine returned pointer range, otherwise meta->mem_size = -1 by default (so it > > > will be -1 for the !tnum_is_const(reg->var_off) case). > > > > > > if (arg_type & ARG_CONST) > > > meta->mem_size = reg->var_off.value; > > > if (!(arg_type & ARG_ZERO) && !meta->mem_size) > > > // error > > > > > > The check_mem_size_reg call is only made when we see that previous reg was > > > ARG_PTR_TO_MEM. When preceding argument is not ARG_PTR_TO_MEM, we error if > > > ARG_CONST is not set for ARG_MEM_SIZE (so that either the mem size is for > > > previous parameter, or otherwise a constant size for the returned pointer). > > > We can also only allow certain pointer return types for that case. > > > > > > If that is too much automagic, we can also discern using ARG_MEM_SIZE vs > > > ARG_RET_MEM_SIZE, but I think the above is fine. > > > > > > ARG_CONST ofcourse only applies to args taking scalar type. > > > > > > > > > > > > > > > > __BPF_ARG_TYPE_MAX, > > > > > > > > > > /* Extended arg_types. */ > > > > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > > > > index ec3a7b6c9515..0373d5bd240f 100644 > > > > > --- a/kernel/bpf/verifier.c > > > > > +++ b/kernel/bpf/verifier.c > > > > > @@ -5163,6 +5163,12 @@ static bool arg_type_is_int_ptr(enum bpf_arg_type type) > > > > > type == ARG_PTR_TO_LONG; > > > > > } > > > > > > > > > > +static bool arg_type_is_scalar(enum bpf_arg_type type) > > > > > +{ > > > > > + return type == ARG_SCALAR || > > > > > + type == ARG_CONSTANT; > > > > > +} > > > > > + > > > > > static int int_ptr_type_to_size(enum bpf_arg_type type) > > > > > { > > > > > if (type == ARG_PTR_TO_INT) > > > > > @@ -5302,6 +5308,8 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = { > > > > > [ARG_PTR_TO_STACK] = &stack_ptr_types, > > > > > [ARG_PTR_TO_CONST_STR] = &const_str_ptr_types, > > > > > [ARG_PTR_TO_TIMER] = &timer_types, > > > > > + [ARG_SCALAR] = &scalar_types, > > > > > + [ARG_CONSTANT] = &scalar_types, > > > > > }; > > > > > > > > > > static int check_reg_type(struct bpf_verifier_env *env, u32 regno, > > > > > @@ -5635,6 +5643,11 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg, > > > > > verbose(env, "string is not zero-terminated\n"); > > > > > return -EINVAL; > > > > > } > > > > > + } else if (arg_type_is_scalar(arg_type)) { > > > > > + if (arg_type == ARG_CONSTANT && !tnum_is_const(reg->var_off)) { > > > > > + verbose(env, "R%d is not a known constant\n", regno); > > > > > + return -EACCES; > > > > > + } > > > > > } > > > > > > > > > > return err; > > > > > -- > > > > > 2.35.1 > > > > > > > > > > > -- > > > Kartikeya -- Kartikeya
diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 88449fbbe063..7841d90b83df 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -391,6 +391,8 @@ enum bpf_arg_type { ARG_PTR_TO_STACK, /* pointer to stack */ ARG_PTR_TO_CONST_STR, /* pointer to a null terminated read-only string */ ARG_PTR_TO_TIMER, /* pointer to bpf_timer */ + ARG_SCALAR, /* a scalar with any value(s) */ + ARG_CONSTANT, /* a scalar with constant value */ __BPF_ARG_TYPE_MAX, /* Extended arg_types. */ diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index ec3a7b6c9515..0373d5bd240f 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -5163,6 +5163,12 @@ static bool arg_type_is_int_ptr(enum bpf_arg_type type) type == ARG_PTR_TO_LONG; } +static bool arg_type_is_scalar(enum bpf_arg_type type) +{ + return type == ARG_SCALAR || + type == ARG_CONSTANT; +} + static int int_ptr_type_to_size(enum bpf_arg_type type) { if (type == ARG_PTR_TO_INT) @@ -5302,6 +5308,8 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = { [ARG_PTR_TO_STACK] = &stack_ptr_types, [ARG_PTR_TO_CONST_STR] = &const_str_ptr_types, [ARG_PTR_TO_TIMER] = &timer_types, + [ARG_SCALAR] = &scalar_types, + [ARG_CONSTANT] = &scalar_types, }; static int check_reg_type(struct bpf_verifier_env *env, u32 regno, @@ -5635,6 +5643,11 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg, verbose(env, "string is not zero-terminated\n"); return -EINVAL; } + } else if (arg_type_is_scalar(arg_type)) { + if (arg_type == ARG_CONSTANT && !tnum_is_const(reg->var_off)) { + verbose(env, "R%d is not a known constant\n", regno); + return -EACCES; + } } return err;
In the next patch, we will introduce a new helper 'bpf_packet_pointer' that takes offset and len and returns a packet pointer. There we want to statically enforce offset is in range [0, 0xffff], and that len is a constant value, in range [1, 0xffff]. This also helps us avoid a pointless runtime check. To make these checks possible, we need to ensure we only get a scalar type. Although a lot of other argument types take scalars, their intent is different. Hence add general ARG_SCALAR and ARG_CONSTANT types, where the latter is also checked to be constant in addition to being scalar. Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> --- include/linux/bpf.h | 2 ++ kernel/bpf/verifier.c | 13 +++++++++++++ 2 files changed, 15 insertions(+)