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bpf: Add strict alignment flag for BPF_PROG_LOAD.

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Add a new field, "prog_flags", and an initial flag value
BPF_F_STRICT_ALIGNMENT.

When set, the verifier will enforce strict pointer alignment
regardless of the setting of CONFIG_EFFICIENT_UNALIGNED_ACCESS.

The verifier, in this mode, will also use a fixed value of "2" in
place of NET_IP_ALIGN.

This facilitates test cases that will exercise and validate this part
of the verifier even when run on architectures where alignment doesn't
matter.

Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
David S. Miller 2017-05-10 11:38:07 -07:00
parent c5fc9692d1
commit e07b98d9bf
6 changed files with 40 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/bpf_verifier.h
View File

@ -90,6 +90,7 @@ struct bpf_verifier_env {
struct bpf_prog *prog; /* eBPF program being verified */
struct bpf_verifier_stack_elem *head; /* stack of verifier states to be processed */
int stack_size; /* number of states to be processed */
bool strict_alignment; /* perform strict pointer alignment checks */
struct bpf_verifier_state cur_state; /* current verifier state */
struct bpf_verifier_state_list **explored_states; /* search pruning optimization */
const struct bpf_ext_analyzer_ops *analyzer_ops; /* external analyzer ops */

8
include/uapi/linux/bpf.h
View File

@ -132,6 +132,13 @@ enum bpf_attach_type {
*/
#define BPF_F_ALLOW_OVERRIDE (1U << 0)
/* If BPF_F_STRICT_ALIGNMENT is used in BPF_PROG_LOAD command, the
* verifier will perform strict alignment checking as if the kernel
* has been built with CONFIG_EFFICIENT_UNALIGNED_ACCESS not set,
* and NET_IP_ALIGN defined to 2.
*/
#define BPF_F_STRICT_ALIGNMENT (1U << 0)
#define BPF_PSEUDO_MAP_FD 1
/* flags for BPF_MAP_UPDATE_ELEM command */
@ -177,6 +184,7 @@ union bpf_attr {
__u32 log_size; /* size of user buffer */
__aligned_u64 log_buf; /* user supplied buffer */
__u32 kern_version; /* checked when prog_type=kprobe */
__u32 prog_flags;
};
struct { /* anonymous struct used by BPF_OBJ_* commands */

5
kernel/bpf/syscall.c
View File

@ -783,7 +783,7 @@ struct bpf_prog *bpf_prog_get_type(u32 ufd, enum bpf_prog_type type)
EXPORT_SYMBOL_GPL(bpf_prog_get_type);
/* last field in 'union bpf_attr' used by this command */
#define BPF_PROG_LOAD_LAST_FIELD kern_version
#define BPF_PROG_LOAD_LAST_FIELD prog_flags
static int bpf_prog_load(union bpf_attr *attr)
{
@ -796,6 +796,9 @@ static int bpf_prog_load(union bpf_attr *attr)
if (CHECK_ATTR(BPF_PROG_LOAD))
return -EINVAL;
if (attr->prog_flags & ~BPF_F_STRICT_ALIGNMENT)
return -EINVAL;
/* copy eBPF program license from user space */
if (strncpy_from_user(license, u64_to_user_ptr(attr->license),
sizeof(license) - 1) < 0)

23
kernel/bpf/verifier.c
View File

@ -791,6 +791,7 @@ static bool is_pointer_value(struct bpf_verifier_env *env, int regno)
static int check_pkt_ptr_alignment(const struct bpf_reg_state *reg,
int off, int size, bool strict)
{
int ip_align;
int reg_off;
/* Byte size accesses are always allowed. */
@ -807,10 +808,14 @@ static int check_pkt_ptr_alignment(const struct bpf_reg_state *reg,
reg_off += reg->aux_off;
}
/* skb->data is NET_IP_ALIGN-ed */
if ((NET_IP_ALIGN + reg_off + off) % size != 0) {
/* skb->data is NET_IP_ALIGN-ed, but for strict alignment checking
* we force this to 2 which is universally what architectures use
* when they don't set CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS.
*/
ip_align = strict ? 2 : NET_IP_ALIGN;
if ((ip_align + reg_off + off) % size != 0) {
verbose("misaligned packet access off %d+%d+%d size %d\n",
NET_IP_ALIGN, reg_off, off, size);
ip_align, reg_off, off, size);
return -EACCES;
}
@ -828,10 +833,11 @@ static int check_val_ptr_alignment(const struct bpf_reg_state *reg,
return 0;
}
static int check_ptr_alignment(const struct bpf_reg_state *reg,
static int check_ptr_alignment(struct bpf_verifier_env *env,
const struct bpf_reg_state *reg,
int off, int size)
{
bool strict = false;
bool strict = env->strict_alignment;
if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
strict = true;
@ -873,7 +879,7 @@ static int check_mem_access(struct bpf_verifier_env *env, u32 regno, int off,
if (size < 0)
return size;
err = check_ptr_alignment(reg, off, size);
err = check_ptr_alignment(env, reg, off, size);
if (err)
return err;
@ -3568,6 +3574,10 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr)
} else {
log_level = 0;
}
if (attr->prog_flags & BPF_F_STRICT_ALIGNMENT)
env->strict_alignment = true;
else
env->strict_alignment = false;
ret = replace_map_fd_with_map_ptr(env);
if (ret < 0)
@ -3673,6 +3683,7 @@ int bpf_analyzer(struct bpf_prog *prog, const struct bpf_ext_analyzer_ops *ops,
mutex_lock(&bpf_verifier_lock);
log_level = 0;
env->strict_alignment = false;
env->explored_states = kcalloc(env->prog->len,
sizeof(struct bpf_verifier_state_list *),

1
tools/build/feature/test-bpf.c
View File

@ -29,6 +29,7 @@ int main(void)
attr.log_size = 0;
attr.log_level = 0;
attr.kern_version = 0;
attr.prog_flags = 0;
/*
* Test existence of __NR_bpf and BPF_PROG_LOAD.

11
tools/include/uapi/linux/bpf.h
View File

@ -132,6 +132,13 @@ enum bpf_attach_type {
*/
#define BPF_F_ALLOW_OVERRIDE (1U << 0)
/* If BPF_F_STRICT_ALIGNMENT is used in BPF_PROG_LOAD command, the
* verifier will perform strict alignment checking as if the kernel
* has been built with CONFIG_EFFICIENT_UNALIGNED_ACCESS not set,
* and NET_IP_ALIGN defined to 2.
*/
#define BPF_F_STRICT_ALIGNMENT (1U << 0)
#define BPF_PSEUDO_MAP_FD 1
/* flags for BPF_MAP_UPDATE_ELEM command */
@ -177,6 +184,7 @@ union bpf_attr {
__u32 log_size; /* size of user buffer */
__aligned_u64 log_buf; /* user supplied buffer */
__u32 kern_version; /* checked when prog_type=kprobe */
__u32 prog_flags;
};
struct { /* anonymous struct used by BPF_OBJ_* commands */
@ -481,8 +489,7 @@ union bpf_attr {
* u32 bpf_get_socket_uid(skb)
* Get the owner uid of the socket stored inside sk_buff.
* @skb: pointer to skb
* Return: uid of the socket owner on success or 0 if the socket pointer
* inside sk_buff is NULL
* Return: uid of the socket owner on success or overflowuid if failed.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \