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Date: Thu, 11 May 2017 12:05:40 -0400 (EDT)
From: David Miller <davem@...emloft.net>
To: daniel@...earbox.net
CC: ast@...com, alexei.starovoitov@...il.com, netdev@...r.kernel.org
Subject: [PATCH v2 3/7] bpf: Add strict alignment flag for BPF_PROG_LOAD.
Add a new field, "prog_flags", and an initial flag value
BPF_F_STRCIT_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@...emloft.net>
Acked-by: Daniel Borkmann <daniel@...earbox.net>
---
include/linux/bpf_verifier.h | 1 +
include/uapi/linux/bpf.h | 8 ++++++++
kernel/bpf/syscall.c | 5 ++++-
kernel/bpf/verifier.c | 23 +++++++++++++++++------
tools/build/feature/test-bpf.c | 1 +
tools/include/uapi/linux/bpf.h | 11 +++++++++--
6 files changed, 40 insertions(+), 9 deletions(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 7c6a519..d5093b5 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 945a1f5..94dfa9d 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 */
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index fd2411f..265a0d8 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -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)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index ff2bfe1..e74fb1b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -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 *),
diff --git a/tools/build/feature/test-bpf.c b/tools/build/feature/test-bpf.c
index ebc6dce..7598361 100644
--- a/tools/build/feature/test-bpf.c
+++ b/tools/build/feature/test-bpf.c
@@ -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.
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index e553529..94dfa9d 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/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 */
@@ -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), \
--
2.7.4
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