On Sat, Apr 9, 2022 at 6:18 AM Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> 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 kptrs, 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 | 160 ++++++++++++++++++++++++++++++++++------
> kernel/bpf/map_in_map.c | 5 +-
> kernel/bpf/syscall.c | 114 +++++++++++++++++++++++++++-
> kernel/bpf/verifier.c | 116 ++++++++++++++++++++++++++++-
> 6 files changed, 399 insertions(+), 27 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index bdb5298735ce..e267db260cb7 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,
> +};
nit: should this be a typedef instead of an enum?
> +
> +struct bpf_map_value_off_desc {
> + u32 offset;
> + u32 btf_id;
> + struct btf *btf;
nit: Since bpf_map_value_off_desc is generic and will support
non-kptrs as well, I think embedding "btf_id" and "btf" in a "union {
} kptr;" would make it more clear that only kptrs will have these
fields used
> +};
> +
> +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_kptrs(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..19c297f9a52f 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_parse_kptrs(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 db7bf05adfc5..28b1d9e9124e 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -3166,9 +3166,16 @@ 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 {
> + u32 type_id;
> u32 off;
> };
>
> @@ -3176,23 +3183,50 @@ static int btf_find_field_struct(const struct btf *btf, const struct btf_type *t
> u32 off, int sz, struct btf_field_info *info)
> {
> 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 -E2BIG;
> + return BTF_FIELD_IGNORE;
> info->off = off;
> - 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)
> +{
> + u32 res_id;
> +
> + /* For PTR, sz is always == 8 */
> + if (!btf_type_is_ptr(t))
> + return BTF_FIELD_IGNORE;
> + t = btf_type_by_id(btf, t->type);
> +
> + if (!btf_type_is_type_tag(t))
> + return BTF_FIELD_IGNORE;
> + /* Reject extra tags */
> + if (btf_type_is_type_tag(btf_type_by_id(btf, t->type)))
> + return -EINVAL;
> + if (strcmp("kptr", __btf_name_by_offset(btf, t->name_off)))
> + return -EINVAL;
> +
> + /* Get the base type */
> + t = btf_type_skip_modifiers(btf, t->type, &res_id);
> + /* Only pointer to struct is allowed */
> + if (!__btf_type_is_struct(t))
> + return -EINVAL;
> +
> + info->type_id = res_id;
> + info->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)
Ah okay. I should have read this patch first before commenting on the
previous one :) I see now why you are passing in info instead of just
returning the offset.
> {
> const struct btf_member *member;
> + struct btf_field_info tmp;
> + 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,
> @@ -3212,24 +3246,38 @@ 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, idx < info_cnt ?
> + &info[idx] : &tmp);
> + if (ret < 0)
> + return ret;
> + break;
> + case BTF_FIELD_KPTR:
> + ret = btf_find_field_kptr(btf, member_type, off, sz, idx < info_cnt ?
> + &info[idx] : &tmp);
> if (ret < 0)
> return ret;
> break;
> default:
> return -EFAULT;
> }
> +
> + if (ret == BTF_FIELD_FOUND && idx >= info_cnt)
> + return -E2BIG;
> + else if (ret == BTF_FIELD_IGNORE)
> + continue;
nit: I think if you check the "ret == BTF_FIELD_IGNORE" first, then
you just need to check idx >= info_cnt instead of "ret ==
BTF_FIELD_FOUND && idx >= info_cnt"
> + ++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;
> + struct btf_field_info tmp;
> + 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);
> @@ -3247,19 +3295,32 @@ 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, idx < info_cnt ?
> + &info[idx] : &tmp);
> + if (ret < 0)
> + return ret;
> + break;
> + case BTF_FIELD_KPTR:
> + ret = btf_find_field_kptr(btf, var_type, off, sz, idx < info_cnt ?
> + &info[idx] : &tmp);
> if (ret < 0)
> return ret;
> break;
> default:
> return -EFAULT;
> }
> +
> + if (ret == BTF_FIELD_FOUND && idx >= info_cnt)
> + return -E2BIG;
> + 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,
> - int field_type, struct btf_field_info *info)
> + int field_type, struct btf_field_info *info, int info_cnt)
> {
> const char *name;
> int sz, align;
> @@ -3275,14 +3336,19 @@ static int btf_find_field(const struct btf *btf, const struct btf_type *t,
> sz = sizeof(struct bpf_timer);
> align = __alignof__(struct bpf_timer);
> break;
> + case BTF_FIELD_KPTR:
> + name = NULL;
I see now why you added the if (name) check in the previous patch.
Maybe that should be part of this patch instead to make it more clear?
> + sz = sizeof(u64);
> + align = 8;
> + break;
> default:
> return -EFAULT;
> }
>
> 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;
> }
>
> @@ -3292,26 +3358,78 @@ static int btf_find_field(const struct btf *btf, const struct btf_type *t,
> */
> int btf_find_spin_lock(const struct btf *btf, const struct btf_type *t)
> {
> - struct btf_field_info info = { .off = -ENOENT };
> + struct btf_field_info info;
> int ret;
>
> - ret = btf_find_field(btf, t, BTF_FIELD_SPIN_LOCK, &info);
> + ret = btf_find_field(btf, t, BTF_FIELD_SPIN_LOCK, &info, 1);
> if (ret < 0)
> return ret;
> + if (!ret)
> + return -ENOENT;
> return info.off;
> }
>
> int btf_find_timer(const struct btf *btf, const struct btf_type *t)
> {
> - struct btf_field_info info = { .off = -ENOENT };
> + struct btf_field_info info;
> int ret;
>
> - ret = btf_find_field(btf, t, BTF_FIELD_TIMER, &info);
> + ret = btf_find_field(btf, t, BTF_FIELD_TIMER, &info, 1);
> if (ret < 0)
> return ret;
> + if (!ret)
> + return -ENOENT;
> return info.off;
> }
>
> +struct bpf_map_value_off *btf_parse_kptrs(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, BTF_FIELD_KPTR, info_arr, ARRAY_SIZE(info_arr));
> + if (ret < 0)
> + return ERR_PTR(ret);
> + if (!ret)
> + return NULL;
> +
> + 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;
tab is kzalloced - I think we can just remove this line
> + for (i = 0; i < nr_off; i++) {
> + const struct btf_type *t;
> + struct btf *off_btf;
> + s32 id;
> +
> + t = btf_type_by_id(btf, info_arr[i].type_id);
> + 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;
> + }
Instead of incrementing tab in every loop iteration, why not just set
"tab->nr_off = nr_off" here after the loop? And then in the end: case
where there's an error, we could just do
while (i--)
btf_put(tab->off[i].btf);
> + 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 cdaa1152436a..edfe691284b0 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>
> @@ -473,12 +474,95 @@ 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_kptrs(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_kptrs(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_kptrs(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);
I think we can get away with not zero-ing out the memory, since we're
going to be memcpying over its contents right after
> + 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_kptrs(map_a), b_has_kptr = map_value_has_kptrs(map_b);
> + int size;
> +
> + if (!a_has_kptr && !b_has_kptr)
> + return true;
> + if (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);
> @@ -640,7 +724,7 @@ 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_kptrs(map))
> return -ENOTSUPP;
>
> if (!(vma->vm_flags & VM_SHARED))
> @@ -820,9 +904,33 @@ 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_parse_kptrs(btf, value_type);
Since btf_parse_kptrs can return back ERR_PTR, I think we need to
check here whether map->kptr_offtab is an ERR_PTR.
> + if (map_value_has_kptrs(map)) {
> + if (!bpf_capable()) {
> + ret = -EPERM;
> + goto free_map_tab;
> + }
> + if (map->map_flags & BPF_F_RDONLY_PROG) {
Why is it an error if BPF_F_RDONLY_PROG is set? Maybe I'm
misunderstanding what BPF_F_RDONLY_PROG means, but why can't a program
have read-only access to the kptr value?
> + 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) {
Out of curiosity, do you also plan to add kptr support in the future
to local storage maps as well?
> + 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;
> }
>
> @@ -1639,7 +1747,7 @@ 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_kptrs(map)) {
> fdput(f);
> return -ENOTSUPP;
> }
Maybe I'm missing something, but I'm not seeing it in this patch - do
we also need to add checks that prohibit userspace programs from
trying to do bpf_map_update_elem syscalls that manipulate kptr map
values?
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 71827d14724a..01d45c5010f9 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -3507,6 +3507,83 @@ int check_ptr_off_reg(struct bpf_verifier_env *env,
> 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 (base_type(reg->type) != PTR_TO_BTF_ID || type_flag(reg->type) != PTR_MAYBE_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;
> +}
> +
> +static int check_map_kptr_access(struct bpf_verifier_env *env, u32 regno,
> + int value_regno, int insn_idx,
> + struct bpf_map_value_off_desc *off_desc)
> +{
> + struct bpf_insn *insn = &env->prog->insnsi[insn_idx];
> + int class = BPF_CLASS(insn->code);
> + struct bpf_reg_state *val_reg;
> +
> + /* Things we already checked for in check_map_access and caller:
> + * - Reject cases where variable offset may touch kptr
> + * - size of access (must be BPF_DW)
> + * - tnum_is_const(reg->var_off)
> + * - off_desc->offset == off + reg->var_off.value
> + */
> + /* Only BPF_[LDX,STX,ST] | BPF_MEM | BPF_DW is supported */
> + if (BPF_MODE(insn->code) != BPF_MEM)
> + goto end;
I think this needs its own verbose statement - the one in end: doesn't
seem to match this error
> +
> + if (class == BPF_LDX) {
> + 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 (class == BPF_STX) {
> + 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 (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 0;
> +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)
> @@ -3545,6 +3622,32 @@ static int check_map_access(struct bpf_verifier_env *env, u32 regno,
> return -EACCES;
> }
> }
> + if (map_value_has_kptrs(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;
> }
>
> @@ -4412,6 +4515,8 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
> if (value_regno >= 0)
> mark_reg_unknown(env, regs, value_regno);
> } else if (reg->type == PTR_TO_MAP_VALUE) {
> + struct bpf_map_value_off_desc *off_desc = NULL;
> +
> if (t == BPF_WRITE && value_regno >= 0 &&
> is_pointer_value(env, value_regno)) {
> verbose(env, "R%d leaks addr into map\n", value_regno);
> @@ -4421,7 +4526,16 @@ 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);
> - if (!err && t == BPF_READ && value_regno >= 0) {
> + if (err)
> + return err;
> + if (tnum_is_const(reg->var_off))
> + off_desc = bpf_map_kptr_off_contains(reg->map_ptr,
> + off + reg->var_off.value);
> + if (off_desc) {
I think this logic would be a little clearer if you renamed off_desc
to kptr_off_desc to denote that this only applies to kptrs.
> + err = check_map_kptr_access(env, regno, value_regno, insn_idx, off_desc);
> + if (err)
> + return err;
I don't think you need this if check - it'll return err by default at
the end of the function.
> + } else if (t == BPF_READ && value_regno >= 0) {
> struct bpf_map *map = reg->map_ptr;
>
> /* if map is read-only, track its contents as scalars */
> --
> 2.35.1
>
