[PATCHv9 bpf-next 1/5] bpf: add a new bpf argument type ARG_CONST_MAP_PTR_OR_NULL

Hangbin Liu
2020-08-26T13:20:43Z

Add a new bpf argument type ARG_CONST_MAP_PTR_OR_NULL which could be
used when we want to allow NULL pointer for map parameter. The bpf helper
need to take care and check if the map is NULL when use this type.

Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
---

v9: merge the patch from [1] in to this series.
v1-v8: no this patch

[1] https://lore.kernel.org/bpf/20200715070001.2048207-1-liuhangbin@gmail.com/
---
include/linux/bpf.h | 2 ++
kernel/bpf/verifier.c | 23 ++++++++++++++++-------
2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a6131d95e31e..cb40a1281ea2 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -276,6 +276,7 @@ enum bpf_arg_type {
ARG_PTR_TO_ALLOC_MEM, /* pointer to dynamically allocated memory */
ARG_PTR_TO_ALLOC_MEM_OR_NULL, /* pointer to dynamically allocated memory or NULL */
ARG_CONST_ALLOC_SIZE_OR_ZERO, /* number of allocated bytes requested */
+ ARG_CONST_MAP_PTR_OR_NULL, /* const argument used as pointer to bpf_map or NULL */
};

/* type of values returned from helper functions */
@@ -369,6 +370,7 @@ enum bpf_reg_type {
PTR_TO_RDONLY_BUF_OR_NULL, /* reg points to a readonly buffer or NULL */
PTR_TO_RDWR_BUF, /* reg points to a read/write buffer */
PTR_TO_RDWR_BUF_OR_NULL, /* reg points to a read/write buffer or NULL */
+ CONST_PTR_TO_MAP_OR_NULL, /* reg points to struct bpf_map or NULL */
};

/* The information passed from prog-specific *_is_valid_access
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 7e5908b83ec7..53a84335a8fd 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -411,7 +411,8 @@ static bool reg_type_may_be_null(enum bpf_reg_type type)
type == PTR_TO_BTF_ID_OR_NULL ||
type == PTR_TO_MEM_OR_NULL ||
type == PTR_TO_RDONLY_BUF_OR_NULL ||
- type == PTR_TO_RDWR_BUF_OR_NULL;
+ type == PTR_TO_RDWR_BUF_OR_NULL ||
+ type == CONST_PTR_TO_MAP_OR_NULL;
}

static bool reg_may_point_to_spin_lock(const struct bpf_reg_state *reg)
@@ -427,7 +428,8 @@ static bool reg_type_may_be_refcounted_or_null(enum bpf_reg_type type)
type == PTR_TO_TCP_SOCK ||
type == PTR_TO_TCP_SOCK_OR_NULL ||
type == PTR_TO_MEM ||
- type == PTR_TO_MEM_OR_NULL;
+ type == PTR_TO_MEM_OR_NULL ||
+ type == CONST_PTR_TO_MAP_OR_NULL;
}

static bool arg_type_may_be_refcounted(enum bpf_arg_type type)
@@ -509,6 +511,7 @@ static const char * const reg_type_str[] = {
[PTR_TO_RDONLY_BUF_OR_NULL] = "rdonly_buf_or_null",
[PTR_TO_RDWR_BUF] = "rdwr_buf",
[PTR_TO_RDWR_BUF_OR_NULL] = "rdwr_buf_or_null",
+ [CONST_PTR_TO_MAP_OR_NULL] = "map_ptr_or_null",
};

static char slot_type_char[] = {
@@ -3957,9 +3960,13 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
expected_type = SCALAR_VALUE;
if (type != expected_type)
goto err_type;
- } else if (arg_type == ARG_CONST_MAP_PTR) {
+ } else if (arg_type == ARG_CONST_MAP_PTR ||
+ arg_type == ARG_CONST_MAP_PTR_OR_NULL) {
expected_type = CONST_PTR_TO_MAP;
- if (type != expected_type)
+ if (register_is_null(reg) &&
+ arg_type == ARG_CONST_MAP_PTR_OR_NULL)
+ /* final test in check_stack_boundary() */;
+ else if (type != expected_type)
goto err_type;
} else if (arg_type == ARG_PTR_TO_CTX ||
arg_type == ARG_PTR_TO_CTX_OR_NULL) {
@@ -4076,9 +4083,9 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
return -EFAULT;
}

- if (arg_type == ARG_CONST_MAP_PTR) {
- /* bpf_map_xxx(map_ptr) call: remember that map_ptr */
- meta->map_ptr = reg->map_ptr;
+ if (arg_type == ARG_CONST_MAP_PTR ||
+ arg_type == ARG_CONST_MAP_PTR_OR_NULL) {
+ meta->map_ptr = register_is_null(reg) ? NULL : reg->map_ptr;
} else if (arg_type == ARG_PTR_TO_MAP_KEY) {
/* bpf_map_xxx(..., map_ptr, ..., key) call:
* check that [key, key + map->key_size) are within
@@ -6977,6 +6984,8 @@ static void mark_ptr_or_null_reg(struct bpf_func_state *state,
reg->type = PTR_TO_RDONLY_BUF;
} else if (reg->type == PTR_TO_RDWR_BUF_OR_NULL) {
reg->type = PTR_TO_RDWR_BUF;
+ } else if (reg->type == CONST_PTR_TO_MAP_OR_NULL) {
+ reg->type = CONST_PTR_TO_MAP;
}
if (is_null) {
/* We don't need id and ref_obj_id from this point
--
2.25.4