bpf: Add strict alignment flag for BPF_PROG_LOAD.

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>

2 files changed, 9 insertions, 0 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 7c6a51924afc..d5093b52b485 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -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 */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 945a1f5f63c5..94dfa9def355 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -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 */