| Message ID | 20200401110907.2669564-2-jolsa@kernel.org |
|---|---|
| State | RFC |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | bpf: Add d_path helper | expand |
On Wed, Apr 01, 2020 at 01:09:05PM +0200, Jiri Olsa wrote: > Adding btf_struct_address function that takes 2 BTF objects > and offset as arguments and checks wether object A is nested > in object B on given offset. > > This function is be used when checking the helper function > PTR_TO_BTF_ID arguments. If the argument has an offset value, > the btf_struct_address will check if the final address is > the expected BTF ID. > > This way we can access nested BTF objects under PTR_TO_BTF_ID > pointer type and pass them to helpers, while they still point > to valid kernel BTF objects. > > Signed-off-by: Jiri Olsa <jolsa@kernel.org> > --- > include/linux/bpf.h | 3 ++ > kernel/bpf/btf.c | 69 +++++++++++++++++++++++++++++++++++++++++++ > kernel/bpf/verifier.c | 18 +++++++++-- > 3 files changed, 88 insertions(+), 2 deletions(-) > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index fd2b2322412d..d3bad7ee60c6 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -1196,6 +1196,9 @@ int btf_struct_access(struct bpf_verifier_log *log, > const struct btf_type *t, int off, int size, > enum bpf_access_type atype, > u32 *next_btf_id); > +int btf_struct_address(struct bpf_verifier_log *log, > + const struct btf_type *t, > + u32 off, u32 exp_id); > int btf_resolve_helper_id(struct bpf_verifier_log *log, > const struct bpf_func_proto *fn, int); > > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c > index d65c6912bdaf..9aafffa57d8b 100644 > --- a/kernel/bpf/btf.c > +++ b/kernel/bpf/btf.c > @@ -4002,6 +4002,75 @@ int btf_struct_access(struct bpf_verifier_log *log, > return -EINVAL; > } > > +int btf_struct_address(struct bpf_verifier_log *log, > + const struct btf_type *t, > + u32 off, u32 exp_id) > +{ > + u32 i, moff, mtrue_end, msize = 0; > + const struct btf_member *member; > + const struct btf_type *mtype; > + const char *tname, *mname; > + > +again: > + tname = __btf_name_by_offset(btf_vmlinux, t->name_off); > + if (!btf_type_is_struct(t)) { > + bpf_log(log, "Type '%s' is not a struct\n", tname); > + return -EINVAL; > + } > + > + if (off > t->size) { > + bpf_log(log, "address beyond struct %s at off %u size %u\n", > + tname, off, t->size); > + return -EACCES; > + } > + > + for_each_member(i, t, member) { > + /* offset of the field in bytes */ > + moff = btf_member_bit_offset(t, member) / 8; > + if (off < moff) > + /* won't find anything, field is already too far */ > + break; > + > + /* we found the member */ > + if (off == moff && member->type == exp_id) > + return 0; > + > + /* type of the field */ > + mtype = btf_type_by_id(btf_vmlinux, member->type); > + mname = __btf_name_by_offset(btf_vmlinux, member->name_off); > + > + mtype = btf_resolve_size(btf_vmlinux, mtype, &msize, > + NULL, NULL); > + if (IS_ERR(mtype)) { > + bpf_log(log, "field %s doesn't have size\n", mname); > + return -EFAULT; > + } > + > + mtrue_end = moff + msize; > + if (off >= mtrue_end) > + /* no overlap with member, keep iterating */ > + continue; > + > + /* the 'off' we're looking for is either equal to start > + * of this field or inside of this struct > + */ > + if (btf_type_is_struct(mtype)) { > + /* our field must be inside that union or struct */ > + t = mtype; > + > + /* adjust offset we're looking for */ > + off -= moff; > + goto again; > + } Looks like copy-paste that should be generalized into common helper. > + > + bpf_log(log, "struct %s doesn't have struct field at offset %d\n", tname, off); > + return -EACCES; > + } > + > + bpf_log(log, "struct %s doesn't have field at offset %d\n", tname, off); > + return -EACCES; > +} > + > static int __btf_resolve_helper_id(struct bpf_verifier_log *log, void *fn, > int arg) > { > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index 04c6630cc18f..6eb88bef4379 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -3103,6 +3103,18 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env, > return 0; > } > > +static void check_ptr_in_btf(struct bpf_verifier_env *env, > + struct bpf_reg_state *reg, > + u32 exp_id) > +{ > + const struct btf_type *t = btf_type_by_id(btf_vmlinux, reg->btf_id); > + > + if (!btf_struct_address(&env->log, t, reg->off, exp_id)) { > + reg->btf_id = exp_id; > + reg->off = 0; This doesn't look right. If you simply overwrite btf_id and off in the reg it will contain wrong info in any subsequent instruction. Typically it would be ok, since this reg is a function argument and will be scratched after the call, but consider: bpf_foo(&file->f_path, &file->f_owner); The same base register will be used to construct R1 and R2 and above re-assign will screw up R1.
On Mon, Apr 06, 2020 at 06:16:01PM -0700, Alexei Starovoitov wrote: SNIP > > + continue; > > + > > + /* the 'off' we're looking for is either equal to start > > + * of this field or inside of this struct > > + */ > > + if (btf_type_is_struct(mtype)) { > > + /* our field must be inside that union or struct */ > > + t = mtype; > > + > > + /* adjust offset we're looking for */ > > + off -= moff; > > + goto again; > > + } > > Looks like copy-paste that should be generalized into common helper. right, I think we could have some common code with btf_struct_access, but id not want to complicate the change for rfc > > > + > > + bpf_log(log, "struct %s doesn't have struct field at offset %d\n", tname, off); > > + return -EACCES; > > + } > > + > > + bpf_log(log, "struct %s doesn't have field at offset %d\n", tname, off); > > + return -EACCES; > > +} > > + > > static int __btf_resolve_helper_id(struct bpf_verifier_log *log, void *fn, > > int arg) > > { > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > > index 04c6630cc18f..6eb88bef4379 100644 > > --- a/kernel/bpf/verifier.c > > +++ b/kernel/bpf/verifier.c > > @@ -3103,6 +3103,18 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env, > > return 0; > > } > > > > +static void check_ptr_in_btf(struct bpf_verifier_env *env, > > + struct bpf_reg_state *reg, > > + u32 exp_id) > > +{ > > + const struct btf_type *t = btf_type_by_id(btf_vmlinux, reg->btf_id); > > + > > + if (!btf_struct_address(&env->log, t, reg->off, exp_id)) { > > + reg->btf_id = exp_id; > > + reg->off = 0; > > This doesn't look right. > If you simply overwrite btf_id and off in the reg it will contain wrong info > in any subsequent instruction. > Typically it would be ok, since this reg is a function argument and will be > scratched after the call, but consider: > bpf_foo(&file->f_path, &file->f_owner); > The same base register will be used to construct R1 and R2 > and above re-assign will screw up R1. ok.. I'll use the 'new btf id' just to do check on the helper args and not change the reg's btf id thanks, jirka
diff --git a/include/linux/bpf.h b/include/linux/bpf.h index fd2b2322412d..d3bad7ee60c6 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -1196,6 +1196,9 @@ int btf_struct_access(struct bpf_verifier_log *log, const struct btf_type *t, int off, int size, enum bpf_access_type atype, u32 *next_btf_id); +int btf_struct_address(struct bpf_verifier_log *log, + const struct btf_type *t, + u32 off, u32 exp_id); int btf_resolve_helper_id(struct bpf_verifier_log *log, const struct bpf_func_proto *fn, int); diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index d65c6912bdaf..9aafffa57d8b 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -4002,6 +4002,75 @@ int btf_struct_access(struct bpf_verifier_log *log, return -EINVAL; } +int btf_struct_address(struct bpf_verifier_log *log, + const struct btf_type *t, + u32 off, u32 exp_id) +{ + u32 i, moff, mtrue_end, msize = 0; + const struct btf_member *member; + const struct btf_type *mtype; + const char *tname, *mname; + +again: + tname = __btf_name_by_offset(btf_vmlinux, t->name_off); + if (!btf_type_is_struct(t)) { + bpf_log(log, "Type '%s' is not a struct\n", tname); + return -EINVAL; + } + + if (off > t->size) { + bpf_log(log, "address beyond struct %s at off %u size %u\n", + tname, off, t->size); + return -EACCES; + } + + for_each_member(i, t, member) { + /* offset of the field in bytes */ + moff = btf_member_bit_offset(t, member) / 8; + if (off < moff) + /* won't find anything, field is already too far */ + break; + + /* we found the member */ + if (off == moff && member->type == exp_id) + return 0; + + /* type of the field */ + mtype = btf_type_by_id(btf_vmlinux, member->type); + mname = __btf_name_by_offset(btf_vmlinux, member->name_off); + + mtype = btf_resolve_size(btf_vmlinux, mtype, &msize, + NULL, NULL); + if (IS_ERR(mtype)) { + bpf_log(log, "field %s doesn't have size\n", mname); + return -EFAULT; + } + + mtrue_end = moff + msize; + if (off >= mtrue_end) + /* no overlap with member, keep iterating */ + continue; + + /* the 'off' we're looking for is either equal to start + * of this field or inside of this struct + */ + if (btf_type_is_struct(mtype)) { + /* our field must be inside that union or struct */ + t = mtype; + + /* adjust offset we're looking for */ + off -= moff; + goto again; + } + + bpf_log(log, "struct %s doesn't have struct field at offset %d\n", tname, off); + return -EACCES; + } + + bpf_log(log, "struct %s doesn't have field at offset %d\n", tname, off); + return -EACCES; +} + static int __btf_resolve_helper_id(struct bpf_verifier_log *log, void *fn, int arg) { diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 04c6630cc18f..6eb88bef4379 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3103,6 +3103,18 @@ static int check_ptr_to_btf_access(struct bpf_verifier_env *env, return 0; } +static void check_ptr_in_btf(struct bpf_verifier_env *env, + struct bpf_reg_state *reg, + u32 exp_id) +{ + const struct btf_type *t = btf_type_by_id(btf_vmlinux, reg->btf_id); + + if (!btf_struct_address(&env->log, t, reg->off, exp_id)) { + reg->btf_id = exp_id; + reg->off = 0; + } +} + /* check whether memory at (regno + off) is accessible for t = (read | write) * if t==write, value_regno is a register which value is stored into memory * if t==read, value_regno is a register which will receive the value from memory @@ -3696,10 +3708,12 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno, expected_type = PTR_TO_BTF_ID; if (type != expected_type) goto err_type; + if (reg->off) + check_ptr_in_btf(env, reg, meta->btf_id); if (reg->btf_id != meta->btf_id) { - verbose(env, "Helper has type %s got %s in R%d\n", + verbose(env, "Helper has type %s got %s in R%d, off %d\n", kernel_type_name(meta->btf_id), - kernel_type_name(reg->btf_id), regno); + kernel_type_name(reg->btf_id), regno, reg->off); return -EACCES; }
Adding btf_struct_address function that takes 2 BTF objects and offset as arguments and checks wether object A is nested in object B on given offset. This function is be used when checking the helper function PTR_TO_BTF_ID arguments. If the argument has an offset value, the btf_struct_address will check if the final address is the expected BTF ID. This way we can access nested BTF objects under PTR_TO_BTF_ID pointer type and pass them to helpers, while they still point to valid kernel BTF objects. Signed-off-by: Jiri Olsa <jolsa@kernel.org> --- include/linux/bpf.h | 3 ++ kernel/bpf/btf.c | 69 +++++++++++++++++++++++++++++++++++++++++++ kernel/bpf/verifier.c | 18 +++++++++-- 3 files changed, 88 insertions(+), 2 deletions(-)