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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
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23
kernel/bpf/verifier.c
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@@ -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 *),