On Sat, Mar 19, 2022 at 11:45:38PM IST, Alexei Starovoitov wrote:
> On Thu, Mar 17, 2022 at 05:29:45PM +0530, Kumar Kartikeya Dwivedi wrote:
> > This commit introduces a new pointer type 'kptr' which can be embedded
> > in a map value as holds a PTR_TO_BTF_ID stored by a BPF program during
> > its invocation. Storing to such a kptr, BPF program's PTR_TO_BTF_ID
> > register must have the same type as in the map value's BTF, and loading
> > a kptr marks the destination register as PTR_TO_BTF_ID with the correct
> > kernel BTF and BTF ID.
> >
> > Such kptr are unreferenced, i.e. by the time another invocation of the
> > BPF program loads this pointer, the object which the pointer points to
> > may not longer exist. Since PTR_TO_BTF_ID loads (using BPF_LDX) are
> > patched to PROBE_MEM loads by the verifier, it would safe to allow user
> > to still access such invalid pointer, but passing such pointers into
> > BPF helpers and kfuncs should not be permitted. A future patch in this
> > series will close this gap.
> >
> > The flexibility offered by allowing programs to dereference such invalid
> > pointers while being safe at runtime frees the verifier from doing
> > complex lifetime tracking. As long as the user may ensure that the
> > object remains valid, it can ensure data read by it from the kernel
> > object is valid.
> >
> > The user indicates that a certain pointer must be treated as kptr
> > capable of accepting stores of PTR_TO_BTF_ID of a certain type, by using
> > a BTF type tag 'kptr' on the pointed to type of the pointer. Then, this
> > information is recorded in the object BTF which will be passed into the
> > kernel by way of map's BTF information. The name and kind from the map
> > value BTF is used to look up the in-kernel type, and the actual BTF and
> > BTF ID is recorded in the map struct in a new kptr_off_tab member. For
> > now, only storing pointers to structs is permitted.
> >
> > An example of this specification is shown below:
> >
> > #define __kptr __attribute__((btf_type_tag("kptr")))
> >
> > struct map_value {
> > ...
> > struct task_struct __kptr *task;
> > ...
> > };
> >
> > Then, in a BPF program, user may store PTR_TO_BTF_ID with the type
> > task_struct into the map, and then load it later.
> >
> > Note that the destination register is marked PTR_TO_BTF_ID_OR_NULL, as
> > the verifier cannot know whether the value is NULL or not statically, it
> > must treat all potential loads at that map value offset as loading a
> > possibly NULL pointer.
> >
> > Only BPF_LDX, BPF_STX, and BPF_ST with insn->imm = 0 (to denote NULL)
> > are allowed instructions that can access such a pointer. On BPF_LDX, the
> > destination register is updated to be a PTR_TO_BTF_ID, and on BPF_STX,
> > it is checked whether the source register type is a PTR_TO_BTF_ID with
> > same BTF type as specified in the map BTF. The access size must always
> > be BPF_DW.
> >
> > For the map in map support, the kptr_off_tab for outer map is copied
> > from the inner map's kptr_off_tab. It was chosen to do a deep copy
> > instead of introducing a refcount to kptr_off_tab, because the copy only
> > needs to be done when paramterizing using inner_map_fd in the map in map
> > case, hence would be unnecessary for all other users.
> >
> > It is not permitted to use MAP_FREEZE command and mmap for BPF map
> > having kptr, similar to the bpf_timer case.
> >
> > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> > ---
> > include/linux/bpf.h | 29 +++++-
> > include/linux/btf.h | 2 +
> > kernel/bpf/btf.c | 151 +++++++++++++++++++++++++----
> > kernel/bpf/map_in_map.c | 5 +-
> > kernel/bpf/syscall.c | 110 ++++++++++++++++++++-
> > kernel/bpf/verifier.c | 207 ++++++++++++++++++++++++++++++++--------
> > 6 files changed, 442 insertions(+), 62 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index 88449fbbe063..f35920d279dd 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -155,6 +155,22 @@ struct bpf_map_ops {
> > const struct bpf_iter_seq_info *iter_seq_info;
> > };
> >
> > +enum {
> > + /* Support at most 8 pointers in a BPF map value */
> > + BPF_MAP_VALUE_OFF_MAX = 8,
> > +};
> > +
> > +struct bpf_map_value_off_desc {
> > + u32 offset;
> > + u32 btf_id;
> > + struct btf *btf;
> > +};
> > +
> > +struct bpf_map_value_off {
> > + u32 nr_off;
> > + struct bpf_map_value_off_desc off[];
> > +};
> > +
> > struct bpf_map {
> > /* The first two cachelines with read-mostly members of which some
> > * are also accessed in fast-path (e.g. ops, max_entries).
> > @@ -171,6 +187,7 @@ struct bpf_map {
> > u64 map_extra; /* any per-map-type extra fields */
> > u32 map_flags;
> > int spin_lock_off; /* >=0 valid offset, <0 error */
> > + struct bpf_map_value_off *kptr_off_tab;
> > int timer_off; /* >=0 valid offset, <0 error */
> > u32 id;
> > int numa_node;
> > @@ -184,7 +201,7 @@ struct bpf_map {
> > char name[BPF_OBJ_NAME_LEN];
> > bool bypass_spec_v1;
> > bool frozen; /* write-once; write-protected by freeze_mutex */
> > - /* 14 bytes hole */
> > + /* 6 bytes hole */
> >
> > /* The 3rd and 4th cacheline with misc members to avoid false sharing
> > * particularly with refcounting.
> > @@ -217,6 +234,11 @@ static inline bool map_value_has_timer(const struct bpf_map *map)
> > return map->timer_off >= 0;
> > }
> >
> > +static inline bool map_value_has_kptr(const struct bpf_map *map)
> > +{
> > + return !IS_ERR_OR_NULL(map->kptr_off_tab);
> > +}
> > +
> > static inline void check_and_init_map_value(struct bpf_map *map, void *dst)
> > {
> > if (unlikely(map_value_has_spin_lock(map)))
> > @@ -1497,6 +1519,11 @@ void bpf_prog_put(struct bpf_prog *prog);
> > void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock);
> > void bpf_map_free_id(struct bpf_map *map, bool do_idr_lock);
> >
> > +struct bpf_map_value_off_desc *bpf_map_kptr_off_contains(struct bpf_map *map, u32 offset);
> > +void bpf_map_free_kptr_off_tab(struct bpf_map *map);
> > +struct bpf_map_value_off *bpf_map_copy_kptr_off_tab(const struct bpf_map *map);
> > +bool bpf_map_equal_kptr_off_tab(const struct bpf_map *map_a, const struct bpf_map *map_b);
> > +
> > struct bpf_map *bpf_map_get(u32 ufd);
> > struct bpf_map *bpf_map_get_with_uref(u32 ufd);
> > struct bpf_map *__bpf_map_get(struct fd f);
> > diff --git a/include/linux/btf.h b/include/linux/btf.h
> > index 36bc09b8e890..5b578dc81c04 100644
> > --- a/include/linux/btf.h
> > +++ b/include/linux/btf.h
> > @@ -123,6 +123,8 @@ bool btf_member_is_reg_int(const struct btf *btf, const struct btf_type *s,
> > u32 expected_offset, u32 expected_size);
> > int btf_find_spin_lock(const struct btf *btf, const struct btf_type *t);
> > int btf_find_timer(const struct btf *btf, const struct btf_type *t);
> > +struct bpf_map_value_off *btf_find_kptr(const struct btf *btf,
> > + const struct btf_type *t);
> > bool btf_type_is_void(const struct btf_type *t);
> > s32 btf_find_by_name_kind(const struct btf *btf, const char *name, u8 kind);
> > const struct btf_type *btf_type_skip_modifiers(const struct btf *btf,
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index 5b2824332880..9ac9364ef533 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -3164,33 +3164,79 @@ static void btf_struct_log(struct btf_verifier_env *env,
> > enum {
> > BTF_FIELD_SPIN_LOCK,
> > BTF_FIELD_TIMER,
> > + BTF_FIELD_KPTR,
> > +};
> > +
> > +enum {
> > + BTF_FIELD_IGNORE = 0,
> > + BTF_FIELD_FOUND = 1,
> > };
> >
> > struct btf_field_info {
> > + const struct btf_type *type;
> > u32 off;
> > };
> >
> > static int btf_find_field_struct(const struct btf *btf, const struct btf_type *t,
> > - u32 off, int sz, struct btf_field_info *info)
> > + u32 off, int sz, struct btf_field_info *info,
> > + int info_cnt, int idx)
> > {
> > if (!__btf_type_is_struct(t))
> > - return 0;
> > + return BTF_FIELD_IGNORE;
> > if (t->size != sz)
> > - return 0;
> > - if (info->off != -ENOENT)
> > - /* only one such field is allowed */
> > + return BTF_FIELD_IGNORE;
> > + if (idx >= info_cnt)
>
> No need to pass info_cnt, idx into this function.
> Move idx >= info_cnt check into the caller and let
> caller do 'info++' and pass that.
That was what I did initially, but this check actually needs to happen after we
see that the field is of interest (i.e. not ignored by btf_find_field_*). Doing
it in caller limits total fields to info_cnt. Moving those checks out into the
caller may be the other option, but I didn't like that. I can add a comment if
it makes things clear.
> This function will simply write into 'info'.
>
> > return -E2BIG;
> > + info[idx].off = off;
> > info->off = off;
>
> This can't be right.
>
Ouch, thanks for catching this.
> > - return 0;
> > + return BTF_FIELD_FOUND;
> > +}
> > +
> > +static int btf_find_field_kptr(const struct btf *btf, const struct btf_type *t,
> > + u32 off, int sz, struct btf_field_info *info,
> > + int info_cnt, int idx)
> > +{
> > + bool kptr_tag = false;
> > +
> > + /* For PTR, sz is always == 8 */
> > + if (!btf_type_is_ptr(t))
> > + return BTF_FIELD_IGNORE;
> > + t = btf_type_by_id(btf, t->type);
> > +
> > + while (btf_type_is_type_tag(t)) {
> > + if (!strcmp("kptr", __btf_name_by_offset(btf, t->name_off))) {
> > + /* repeated tag */
> > + if (kptr_tag)
> > + return -EEXIST;
> > + kptr_tag = true;
> > + }
> > + /* Look for next tag */
> > + t = btf_type_by_id(btf, t->type);
> > + }
>
> There is no need for while() loop and 4 bool kptr_*_tag checks.
> Just do:
> if (!btf_type_is_type_tag(t))
> return BTF_FIELD_IGNORE;
> /* check next tag */
> if (btf_type_is_type_tag(btf_type_by_id(btf, t->type))
> return -EINVAL;
But there may be other tags also in the future? Then on older kernels it would
return an error, instead of skipping over them and ignoring them.
> if (!strcmp("kptr", __btf_name_by_offset(btf, t->name_off)))
> flag = 0;
> else if (!strcmp("kptr_ref", __btf_name_by_offset(btf, t->name_off)))
> flag = BPF_MAP_VALUE_OFF_F_REF;
> ...
>
> > + if (!kptr_tag)
> > + return BTF_FIELD_IGNORE;
> > +
> > + /* Get the base type */
> > + if (btf_type_is_modifier(t))
> > + t = btf_type_skip_modifiers(btf, t->type, NULL);
> > + /* Only pointer to struct is allowed */
> > + if (!__btf_type_is_struct(t))
> > + return -EINVAL;
> > +
> > + if (idx >= info_cnt)
> > + return -E2BIG;
> > + info[idx].type = t;
> > + info[idx].off = off;
> > + return BTF_FIELD_FOUND;
> > }
> >
> > static int btf_find_struct_field(const struct btf *btf, const struct btf_type *t,
> > const char *name, int sz, int align, int field_type,
> > - struct btf_field_info *info)
> > + struct btf_field_info *info, int info_cnt)
> > {
> > const struct btf_member *member;
> > + int ret, idx = 0;
> > u32 i, off;
> > - int ret;
> >
> > for_each_member(i, t, member) {
> > const struct btf_type *member_type = btf_type_by_id(btf,
> > @@ -3210,24 +3256,33 @@ static int btf_find_struct_field(const struct btf *btf, const struct btf_type *t
> > switch (field_type) {
> > case BTF_FIELD_SPIN_LOCK:
> > case BTF_FIELD_TIMER:
> > - ret = btf_find_field_struct(btf, member_type, off, sz, info);
> > + ret = btf_find_field_struct(btf, member_type, off, sz, info, info_cnt, idx);
> > + if (ret < 0)
> > + return ret;
> > + break;
> > + case BTF_FIELD_KPTR:
> > + ret = btf_find_field_kptr(btf, member_type, off, sz, info, info_cnt, idx);
> > if (ret < 0)
> > return ret;
> > break;
> > default:
> > return -EFAULT;
> > }
> > +
> > + if (ret == BTF_FIELD_IGNORE)
> > + continue;
> > + ++idx;
> > }
> > - return 0;
> > + return idx;
> > }
> >
> > static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t,
> > const char *name, int sz, int align, int field_type,
> > - struct btf_field_info *info)
> > + struct btf_field_info *info, int info_cnt)
> > {
> > const struct btf_var_secinfo *vsi;
> > + int ret, idx = 0;
> > u32 i, off;
> > - int ret;
> >
> > for_each_vsi(i, t, vsi) {
> > const struct btf_type *var = btf_type_by_id(btf, vsi->type);
> > @@ -3245,25 +3300,34 @@ static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t,
> > switch (field_type) {
> > case BTF_FIELD_SPIN_LOCK:
> > case BTF_FIELD_TIMER:
> > - ret = btf_find_field_struct(btf, var_type, off, sz, info);
> > + ret = btf_find_field_struct(btf, var_type, off, sz, info, info_cnt, idx);
> > + if (ret < 0)
> > + return ret;
> > + break;
> > + case BTF_FIELD_KPTR:
> > + ret = btf_find_field_kptr(btf, var_type, off, sz, info, info_cnt, idx);
> > if (ret < 0)
> > return ret;
> > break;
> > default:
> > return -EFAULT;
> > }
> > +
> > + if (ret == BTF_FIELD_IGNORE)
> > + continue;
> > + ++idx;
> > }
> > - return 0;
> > + return idx;
> > }
> >
> > static int btf_find_field(const struct btf *btf, const struct btf_type *t,
> > const char *name, int sz, int align, int field_type,
> > - struct btf_field_info *info)
> > + struct btf_field_info *info, int info_cnt)
> > {
> > if (__btf_type_is_struct(t))
> > - return btf_find_struct_field(btf, t, name, sz, align, field_type, info);
> > + return btf_find_struct_field(btf, t, name, sz, align, field_type, info, info_cnt);
> > else if (btf_type_is_datasec(t))
> > - return btf_find_datasec_var(btf, t, name, sz, align, field_type, info);
> > + return btf_find_datasec_var(btf, t, name, sz, align, field_type, info, info_cnt);
> > return -EINVAL;
> > }
> >
> > @@ -3279,7 +3343,7 @@ int btf_find_spin_lock(const struct btf *btf, const struct btf_type *t)
> > ret = btf_find_field(btf, t, "bpf_spin_lock",
> > sizeof(struct bpf_spin_lock),
> > __alignof__(struct bpf_spin_lock),
> > - BTF_FIELD_SPIN_LOCK, &info);
> > + BTF_FIELD_SPIN_LOCK, &info, 1);
> > if (ret < 0)
> > return ret;
> > return info.off;
> > @@ -3293,12 +3357,61 @@ int btf_find_timer(const struct btf *btf, const struct btf_type *t)
> > ret = btf_find_field(btf, t, "bpf_timer",
> > sizeof(struct bpf_timer),
> > __alignof__(struct bpf_timer),
> > - BTF_FIELD_TIMER, &info);
> > + BTF_FIELD_TIMER, &info, 1);
> > if (ret < 0)
> > return ret;
> > return info.off;
> > }
> >
> > +struct bpf_map_value_off *btf_find_kptr(const struct btf *btf,
> > + const struct btf_type *t)
> > +{
> > + struct btf_field_info info_arr[BPF_MAP_VALUE_OFF_MAX];
> > + struct bpf_map_value_off *tab;
> > + int ret, i, nr_off;
> > +
> > + /* Revisit stack usage when bumping BPF_MAP_VALUE_OFF_MAX */
> > + BUILD_BUG_ON(BPF_MAP_VALUE_OFF_MAX != 8);
> > +
> > + ret = btf_find_field(btf, t, NULL, sizeof(u64), __alignof__(u64),
>
> these pointless args will be gone with suggestion in the previous patch.
>
Agreed, will change.
> > + BTF_FIELD_KPTR, info_arr, ARRAY_SIZE(info_arr));
> > + if (ret < 0)
> > + return ERR_PTR(ret);
> > + if (!ret)
> > + return 0;
> > +
> > + nr_off = ret;
> > + tab = kzalloc(offsetof(struct bpf_map_value_off, off[nr_off]), GFP_KERNEL | __GFP_NOWARN);
> > + if (!tab)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + tab->nr_off = 0;
> > + for (i = 0; i < nr_off; i++) {
> > + const struct btf_type *t;
> > + struct btf *off_btf;
> > + s32 id;
> > +
> > + t = info_arr[i].type;
> > + id = bpf_find_btf_id(__btf_name_by_offset(btf, t->name_off), BTF_INFO_KIND(t->info),
> > + &off_btf);
> > + if (id < 0) {
> > + ret = id;
> > + goto end;
> > + }
> > +
> > + tab->off[i].offset = info_arr[i].off;
> > + tab->off[i].btf_id = id;
> > + tab->off[i].btf = off_btf;
> > + tab->nr_off = i + 1;
> > + }
> > + return tab;
> > +end:
> > + while (tab->nr_off--)
> > + btf_put(tab->off[tab->nr_off].btf);
> > + kfree(tab);
> > + return ERR_PTR(ret);
> > +}
> > +
> > static void __btf_struct_show(const struct btf *btf, const struct btf_type *t,
> > u32 type_id, void *data, u8 bits_offset,
> > struct btf_show *show)
> > diff --git a/kernel/bpf/map_in_map.c b/kernel/bpf/map_in_map.c
> > index 5cd8f5277279..135205d0d560 100644
> > --- a/kernel/bpf/map_in_map.c
> > +++ b/kernel/bpf/map_in_map.c
> > @@ -52,6 +52,7 @@ struct bpf_map *bpf_map_meta_alloc(int inner_map_ufd)
> > inner_map_meta->max_entries = inner_map->max_entries;
> > inner_map_meta->spin_lock_off = inner_map->spin_lock_off;
> > inner_map_meta->timer_off = inner_map->timer_off;
> > + inner_map_meta->kptr_off_tab = bpf_map_copy_kptr_off_tab(inner_map);
> > if (inner_map->btf) {
> > btf_get(inner_map->btf);
> > inner_map_meta->btf = inner_map->btf;
> > @@ -71,6 +72,7 @@ struct bpf_map *bpf_map_meta_alloc(int inner_map_ufd)
> >
> > void bpf_map_meta_free(struct bpf_map *map_meta)
> > {
> > + bpf_map_free_kptr_off_tab(map_meta);
> > btf_put(map_meta->btf);
> > kfree(map_meta);
> > }
> > @@ -83,7 +85,8 @@ bool bpf_map_meta_equal(const struct bpf_map *meta0,
> > meta0->key_size == meta1->key_size &&
> > meta0->value_size == meta1->value_size &&
> > meta0->timer_off == meta1->timer_off &&
> > - meta0->map_flags == meta1->map_flags;
> > + meta0->map_flags == meta1->map_flags &&
> > + bpf_map_equal_kptr_off_tab(meta0, meta1);
> > }
> >
> > void *bpf_map_fd_get_ptr(struct bpf_map *map,
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index 9beb585be5a6..87263b07f40b 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -6,6 +6,7 @@
> > #include <linux/bpf_trace.h>
> > #include <linux/bpf_lirc.h>
> > #include <linux/bpf_verifier.h>
> > +#include <linux/bsearch.h>
> > #include <linux/btf.h>
> > #include <linux/syscalls.h>
> > #include <linux/slab.h>
> > @@ -472,12 +473,95 @@ static void bpf_map_release_memcg(struct bpf_map *map)
> > }
> > #endif
> >
> > +static int bpf_map_kptr_off_cmp(const void *a, const void *b)
> > +{
> > + const struct bpf_map_value_off_desc *off_desc1 = a, *off_desc2 = b;
> > +
> > + if (off_desc1->offset < off_desc2->offset)
> > + return -1;
> > + else if (off_desc1->offset > off_desc2->offset)
> > + return 1;
> > + return 0;
> > +}
> > +
> > +struct bpf_map_value_off_desc *bpf_map_kptr_off_contains(struct bpf_map *map, u32 offset)
> > +{
> > + /* Since members are iterated in btf_find_field in increasing order,
> > + * offsets appended to kptr_off_tab are in increasing order, so we can
> > + * do bsearch to find exact match.
> > + */
> > + struct bpf_map_value_off *tab;
> > +
> > + if (!map_value_has_kptr(map))
> > + return NULL;
> > + tab = map->kptr_off_tab;
> > + return bsearch(&offset, tab->off, tab->nr_off, sizeof(tab->off[0]), bpf_map_kptr_off_cmp);
> > +}
> > +
> > +void bpf_map_free_kptr_off_tab(struct bpf_map *map)
> > +{
> > + struct bpf_map_value_off *tab = map->kptr_off_tab;
> > + int i;
> > +
> > + if (!map_value_has_kptr(map))
> > + return;
> > + for (i = 0; i < tab->nr_off; i++) {
> > + struct btf *btf = tab->off[i].btf;
> > +
> > + btf_put(btf);
> > + }
> > + kfree(tab);
> > + map->kptr_off_tab = NULL;
> > +}
> > +
> > +struct bpf_map_value_off *bpf_map_copy_kptr_off_tab(const struct bpf_map *map)
> > +{
> > + struct bpf_map_value_off *tab = map->kptr_off_tab, *new_tab;
> > + int size, i, ret;
> > +
> > + if (!map_value_has_kptr(map))
> > + return ERR_PTR(-ENOENT);
> > + /* Do a deep copy of the kptr_off_tab */
> > + for (i = 0; i < tab->nr_off; i++)
> > + btf_get(tab->off[i].btf);
> > +
> > + size = offsetof(struct bpf_map_value_off, off[tab->nr_off]);
> > + new_tab = kzalloc(size, GFP_KERNEL | __GFP_NOWARN);
> > + if (!new_tab) {
> > + ret = -ENOMEM;
> > + goto end;
> > + }
> > + memcpy(new_tab, tab, size);
> > + return new_tab;
> > +end:
> > + while (i--)
> > + btf_put(tab->off[i].btf);
> > + return ERR_PTR(ret);
> > +}
> > +
> > +bool bpf_map_equal_kptr_off_tab(const struct bpf_map *map_a, const struct bpf_map *map_b)
> > +{
> > + struct bpf_map_value_off *tab_a = map_a->kptr_off_tab, *tab_b = map_b->kptr_off_tab;
> > + bool a_has_kptr = map_value_has_kptr(map_a), b_has_kptr = map_value_has_kptr(map_b);
> > + int size;
> > +
> > + if (!a_has_kptr && !b_has_kptr)
> > + return true;
> > + if ((a_has_kptr && !b_has_kptr) || (!a_has_kptr && b_has_kptr))
> > + return false;
> > + if (tab_a->nr_off != tab_b->nr_off)
> > + return false;
> > + size = offsetof(struct bpf_map_value_off, off[tab_a->nr_off]);
> > + return !memcmp(tab_a, tab_b, size);
> > +}
> > +
> > /* called from workqueue */
> > static void bpf_map_free_deferred(struct work_struct *work)
> > {
> > struct bpf_map *map = container_of(work, struct bpf_map, work);
> >
> > security_bpf_map_free(map);
> > + bpf_map_free_kptr_off_tab(map);
> > bpf_map_release_memcg(map);
> > /* implementation dependent freeing */
> > map->ops->map_free(map);
> > @@ -639,7 +723,7 @@ static int bpf_map_mmap(struct file *filp, struct vm_area_struct *vma)
> > int err;
> >
> > if (!map->ops->map_mmap || map_value_has_spin_lock(map) ||
> > - map_value_has_timer(map))
> > + map_value_has_timer(map) || map_value_has_kptr(map))
> > return -ENOTSUPP;
> >
> > if (!(vma->vm_flags & VM_SHARED))
> > @@ -819,9 +903,29 @@ static int map_check_btf(struct bpf_map *map, const struct btf *btf,
> > return -EOPNOTSUPP;
> > }
> >
> > - if (map->ops->map_check_btf)
> > + map->kptr_off_tab = btf_find_kptr(btf, value_type);
> > + if (map_value_has_kptr(map)) {
> > + if (map->map_flags & BPF_F_RDONLY_PROG) {
> > + ret = -EACCES;
> > + goto free_map_tab;
> > + }
> > + if (map->map_type != BPF_MAP_TYPE_HASH &&
> > + map->map_type != BPF_MAP_TYPE_LRU_HASH &&
> > + map->map_type != BPF_MAP_TYPE_ARRAY) {
> > + ret = -EOPNOTSUPP;
> > + goto free_map_tab;
> > + }
> > + }
> > +
> > + if (map->ops->map_check_btf) {
> > ret = map->ops->map_check_btf(map, btf, key_type, value_type);
> > + if (ret < 0)
> > + goto free_map_tab;
> > + }
> >
> > + return ret;
> > +free_map_tab:
> > + bpf_map_free_kptr_off_tab(map);
> > return ret;
> > }
> >
> > @@ -1638,7 +1742,7 @@ static int map_freeze(const union bpf_attr *attr)
> > return PTR_ERR(map);
> >
> > if (map->map_type == BPF_MAP_TYPE_STRUCT_OPS ||
> > - map_value_has_timer(map)) {
> > + map_value_has_timer(map) || map_value_has_kptr(map)) {
> > fdput(f);
> > return -ENOTSUPP;
> > }
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index cf92f9c01556..881d1381757b 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -3469,6 +3469,143 @@ static int check_mem_region_access(struct bpf_verifier_env *env, u32 regno,
> > return 0;
> > }
> >
> > +static int __check_ptr_off_reg(struct bpf_verifier_env *env,
> > + const struct bpf_reg_state *reg, int regno,
> > + bool fixed_off_ok)
> > +{
> > + /* Access to this pointer-typed register or passing it to a helper
> > + * is only allowed in its original, unmodified form.
> > + */
> > +
> > + if (reg->off < 0) {
> > + verbose(env, "negative offset %s ptr R%d off=%d disallowed\n",
> > + reg_type_str(env, reg->type), regno, reg->off);
> > + return -EACCES;
> > + }
> > +
> > + if (!fixed_off_ok && reg->off) {
> > + verbose(env, "dereference of modified %s ptr R%d off=%d disallowed\n",
> > + reg_type_str(env, reg->type), regno, reg->off);
> > + return -EACCES;
> > + }
> > +
> > + if (!tnum_is_const(reg->var_off) || reg->var_off.value) {
> > + char tn_buf[48];
> > +
> > + tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off);
> > + verbose(env, "variable %s access var_off=%s disallowed\n",
> > + reg_type_str(env, reg->type), tn_buf);
> > + return -EACCES;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +int check_ptr_off_reg(struct bpf_verifier_env *env,
> > + const struct bpf_reg_state *reg, int regno)
> > +{
> > + return __check_ptr_off_reg(env, reg, regno, false);
> > +}
> > +
> > +static int map_kptr_match_type(struct bpf_verifier_env *env,
> > + struct bpf_map_value_off_desc *off_desc,
> > + struct bpf_reg_state *reg, u32 regno)
> > +{
> > + const char *targ_name = kernel_type_name(off_desc->btf, off_desc->btf_id);
> > + const char *reg_name = "";
> > +
> > + if (reg->type != PTR_TO_BTF_ID && reg->type != PTR_TO_BTF_ID_OR_NULL)
> > + goto bad_type;
> > +
> > + if (!btf_is_kernel(reg->btf)) {
> > + verbose(env, "R%d must point to kernel BTF\n", regno);
> > + return -EINVAL;
> > + }
> > + /* We need to verify reg->type and reg->btf, before accessing reg->btf */
> > + reg_name = kernel_type_name(reg->btf, reg->btf_id);
> > +
> > + if (__check_ptr_off_reg(env, reg, regno, true))
> > + return -EACCES;
> > +
> > + if (!btf_struct_ids_match(&env->log, reg->btf, reg->btf_id, reg->off,
> > + off_desc->btf, off_desc->btf_id))
> > + goto bad_type;
> > + return 0;
> > +bad_type:
> > + verbose(env, "invalid kptr access, R%d type=%s%s ", regno,
> > + reg_type_str(env, reg->type), reg_name);
> > + verbose(env, "expected=%s%s\n", reg_type_str(env, PTR_TO_BTF_ID), targ_name);
> > + return -EINVAL;
> > +}
> > +
> > +/* Returns an error, or 0 if ignoring the access, or 1 if register state was
> > + * updated, in which case later updates must be skipped.
> > + */
> > +static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,
> > + int off, int size, int value_regno,
> > + enum bpf_access_type t, int insn_idx)
> > +{
> > + struct bpf_reg_state *reg = reg_state(env, regno), *val_reg;
> > + struct bpf_insn *insn = &env->prog->insnsi[insn_idx];
> > + struct bpf_map_value_off_desc *off_desc;
> > + int insn_class = BPF_CLASS(insn->code);
> > + struct bpf_map *map = reg->map_ptr;
> > +
> > + /* Things we already checked for in check_map_access:
> > + * - Reject cases where variable offset may touch BTF ID pointer
> > + * - size of access (must be BPF_DW)
> > + * - off_desc->offset == off + reg->var_off.value
> > + */
> > + if (!tnum_is_const(reg->var_off))
> > + return 0;
> > +
> > + off_desc = bpf_map_kptr_off_contains(map, off + reg->var_off.value);
> > + if (!off_desc)
> > + return 0;
> > +
> > + if (WARN_ON_ONCE(size != bpf_size_to_bytes(BPF_DW)))
>
> since the check was made, please avoid defensive progamming.
>
Ok.
> > + return -EACCES;
> > +
> > + if (BPF_MODE(insn->code) != BPF_MEM)
>
> what is this? a fancy way to filter ldx/stx/st insns?
> Pls add a comment if so.
>
> > + goto end;
> > +
> > + if (!env->bpf_capable) {
> > + verbose(env, "kptr access only allowed for CAP_BPF and CAP_SYS_ADMIN\n");
> > + return -EPERM;
>
> Please move this check into map_check_btf().
> That's the earliest place we can issue such error.
> Doing it here is so late and it doesn't help users, but makes run-time slower,
> since this function is called a lot more times than map_check_btf.
>
Ok, will do.
> > + }
> > +
> > + if (insn_class == BPF_LDX) {
> > + if (WARN_ON_ONCE(value_regno < 0))
> > + return -EFAULT;
>
> defensive programming? Pls dont.
>
Ok.
> > + val_reg = reg_state(env, value_regno);
> > + /* We can simply mark the value_regno receiving the pointer
> > + * value from map as PTR_TO_BTF_ID, with the correct type.
> > + */
> > + mark_btf_ld_reg(env, cur_regs(env), value_regno, PTR_TO_BTF_ID, off_desc->btf,
> > + off_desc->btf_id, PTR_MAYBE_NULL);
> > + val_reg->id = ++env->id_gen;
> > + } else if (insn_class == BPF_STX) {
> > + if (WARN_ON_ONCE(value_regno < 0))
> > + return -EFAULT;
> > + val_reg = reg_state(env, value_regno);
> > + if (!register_is_null(val_reg) &&
> > + map_kptr_match_type(env, off_desc, val_reg, value_regno))
> > + return -EACCES;
> > + } else if (insn_class == BPF_ST) {
> > + if (insn->imm) {
> > + verbose(env, "BPF_ST imm must be 0 when storing to kptr at off=%u\n",
> > + off_desc->offset);
> > + return -EACCES;
> > + }
> > + } else {
> > + goto end;
> > + }
> > + return 1;
> > +end:
> > + verbose(env, "kptr in map can only be accessed using BPF_LDX/BPF_STX/BPF_ST\n");
> > + return -EACCES;
> > +}
> > +
> > /* check read/write into a map element with possible variable offset */
> > static int check_map_access(struct bpf_verifier_env *env, u32 regno,
> > int off, int size, bool zero_size_allowed)
> > @@ -3507,6 +3644,32 @@ static int check_map_access(struct bpf_verifier_env *env, u32 regno,
> > return -EACCES;
> > }
> > }
> > + if (map_value_has_kptr(map)) {
> > + struct bpf_map_value_off *tab = map->kptr_off_tab;
> > + int i;
> > +
> > + for (i = 0; i < tab->nr_off; i++) {
> > + u32 p = tab->off[i].offset;
> > +
> > + if (reg->smin_value + off < p + sizeof(u64) &&
> > + p < reg->umax_value + off + size) {
> > + if (!tnum_is_const(reg->var_off)) {
> > + verbose(env, "kptr access cannot have variable offset\n");
> > + return -EACCES;
> > + }
> > + if (p != off + reg->var_off.value) {
> > + verbose(env, "kptr access misaligned expected=%u off=%llu\n",
> > + p, off + reg->var_off.value);
> > + return -EACCES;
> > + }
> > + if (size != bpf_size_to_bytes(BPF_DW)) {
> > + verbose(env, "kptr access size must be BPF_DW\n");
> > + return -EACCES;
> > + }
> > + break;
> > + }
> > + }
> > + }
> > return err;
> > }
> >
> > @@ -3980,44 +4143,6 @@ static int get_callee_stack_depth(struct bpf_verifier_env *env,
> > }
> > #endif
> >
> > -static int __check_ptr_off_reg(struct bpf_verifier_env *env,
> > - const struct bpf_reg_state *reg, int regno,
> > - bool fixed_off_ok)
> > -{
> > - /* Access to this pointer-typed register or passing it to a helper
> > - * is only allowed in its original, unmodified form.
> > - */
> > -
> > - if (reg->off < 0) {
> > - verbose(env, "negative offset %s ptr R%d off=%d disallowed\n",
> > - reg_type_str(env, reg->type), regno, reg->off);
> > - return -EACCES;
> > - }
> > -
> > - if (!fixed_off_ok && reg->off) {
> > - verbose(env, "dereference of modified %s ptr R%d off=%d disallowed\n",
> > - reg_type_str(env, reg->type), regno, reg->off);
> > - return -EACCES;
> > - }
> > -
> > - if (!tnum_is_const(reg->var_off) || reg->var_off.value) {
> > - char tn_buf[48];
> > -
> > - tnum_strn(tn_buf, sizeof(tn_buf), reg->var_off);
> > - verbose(env, "variable %s access var_off=%s disallowed\n",
> > - reg_type_str(env, reg->type), tn_buf);
> > - return -EACCES;
> > - }
> > -
> > - return 0;
> > -}
> > -
> > -int check_ptr_off_reg(struct bpf_verifier_env *env,
> > - const struct bpf_reg_state *reg, int regno)
> > -{
> > - return __check_ptr_off_reg(env, reg, regno, false);
> > -}
> > -
>
> please split the hunk that moves code around into separate patch.
> Don't mix it with actual changes.
>
Ok, will split into a separate patch.
> > static int __check_buffer_access(struct bpf_verifier_env *env,
> > const char *buf_info,
> > const struct bpf_reg_state *reg,
> > @@ -4421,6 +4546,10 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
> > if (err)
> > return err;
> > err = check_map_access(env, regno, off, size, false);
> > + err = err ?: check_map_kptr_access(env, regno, off, size, value_regno, t, insn_idx);
> > + if (err < 0)
> > + return err;
> > + /* if err == 0, check_map_kptr_access ignored the access */
> > if (!err && t == BPF_READ && value_regno >= 0) {
> > struct bpf_map *map = reg->map_ptr;
> >
> > @@ -4442,6 +4571,8 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
> > mark_reg_unknown(env, regs, value_regno);
> > }
> > }
> > + /* clear err == 1 */
> > + err = err < 0 ? err : 0;
> > } else if (base_type(reg->type) == PTR_TO_MEM) {
> > bool rdonly_mem = type_is_rdonly_mem(reg->type);
> >
> > --
> > 2.35.1
> >
>
> --
--
Kartikeya
