On 12/7/23 4:05 PM, Eduard Zingerman wrote:
Add __attribute__((preserve_static_offset)) for the following BPF
related structures:
- __sk_buff
- bpf_cgroup_dev_ctx
- bpf_perf_event_data
- bpf_sk_lookup
- bpf_sock
- bpf_sock_addr
- bpf_sock_ops
- bpf_sockopt
- bpf_sysctl
- sk_msg_md
- sk_reuseport_md
- xdp_md
Access to these structures is rewritten by BPF verifier.
(See verifier.c:convert_ctx_access).
The rewrite requires that offsets used in access to fields of these
structures are constant values. __attribute__((preserve_static_offset))
is a hint to clang that ensures that constant offsets are used.
(See https://reviews.llvm.org/D133361 for details).
Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
---
include/uapi/linux/bpf.h | 28 ++++++++++++++---------
include/uapi/linux/bpf_perf_event.h | 8 ++++++-
tools/include/uapi/linux/bpf.h | 28 ++++++++++++++---------
tools/include/uapi/linux/bpf_perf_event.h | 8 ++++++-
4 files changed, 48 insertions(+), 24 deletions(-)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index e0545201b55f..75eee56ed732 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -69,6 +69,12 @@ enum {
/* BPF has 10 general purpose 64-bit registers and stack frame. */
#define MAX_BPF_REG __MAX_BPF_REG
+#if __has_attribute(preserve_static_offset) && defined(__bpf__)
+#define __bpf_ctx __attribute__((preserve_static_offset))
+#else
+#define __bpf_ctx
+#endif
+
struct bpf_insn {
__u8 code; /* opcode */
__u8 dst_reg:4; /* dest register */
@@ -6190,7 +6196,7 @@ struct __sk_buff {
__u8 tstamp_type;
__u32 :24; /* Padding, future use. */
__u64 hwtstamp;
-};
+} __bpf_ctx;
struct bpf_tunnel_key {
__u32 tunnel_id;
@@ -6271,7 +6277,7 @@ struct bpf_sock {
__u32 dst_ip6[4];
__u32 state;
__s32 rx_queue_mapping;
-};
+} __bpf_ctx;
struct bpf_tcp_sock {
__u32 snd_cwnd; /* Sending congestion window */
@@ -6379,7 +6385,7 @@ struct xdp_md {
__u32 rx_queue_index; /* rxq->queue_index */
__u32 egress_ifindex; /* txq->dev->ifindex */
-};
+} __bpf_ctx;
/* DEVMAP map-value layout
*
@@ -6429,7 +6435,7 @@ struct sk_msg_md {
__u32 size; /* Total size of sk_msg */
__bpf_md_ptr(struct bpf_sock *, sk); /* current socket */
-};
+} __bpf_ctx;
struct sk_reuseport_md {
/*
@@ -6468,7 +6474,7 @@ struct sk_reuseport_md {
*/
__bpf_md_ptr(struct bpf_sock *, sk);
__bpf_md_ptr(struct bpf_sock *, migrating_sk);
-};
+} __bpf_ctx;
#define BPF_TAG_SIZE 8
@@ -6678,7 +6684,7 @@ struct bpf_sock_addr {
* Stored in network byte order.
*/
__bpf_md_ptr(struct bpf_sock *, sk);
-};
+} __bpf_ctx;
/* User bpf_sock_ops struct to access socket values and specify request ops
* and their replies.
@@ -6761,7 +6767,7 @@ struct bpf_sock_ops {
* been written yet.
*/
__u64 skb_hwtstamp;
-};
+} __bpf_ctx;
/* Definitions for bpf_sock_ops_cb_flags */
enum {
@@ -7034,7 +7040,7 @@ struct bpf_cgroup_dev_ctx {
__u32 access_type;
__u32 major;
__u32 minor;
-};
+} __bpf_ctx;
struct bpf_raw_tracepoint_args {
__u64 args[0];
@@ -7245,7 +7251,7 @@ struct bpf_sysctl {
__u32 file_pos; /* Sysctl file position to read from, write to.
* Allows 1,2,4-byte read an 4-byte write.
*/
-};
+} __bpf_ctx;
struct bpf_sockopt {
__bpf_md_ptr(struct bpf_sock *, sk);
@@ -7256,7 +7262,7 @@ struct bpf_sockopt {
__s32 optname;
__s32 optlen;
__s32 retval;
-};
+} __bpf_ctx;
struct bpf_pidns_info {
__u32 pid;
@@ -7280,7 +7286,7 @@ struct bpf_sk_lookup {
__u32 local_ip6[4]; /* Network byte order */
__u32 local_port; /* Host byte order */
__u32 ingress_ifindex; /* The arriving interface. Determined by inet_iif. */
-};
+} __bpf_ctx;
should we undef __bpf_ctx at the end of the file?
The same for below bpf_perf_event.h file.
/*
* struct btf_ptr is used for typed pointer representation; the
diff --git a/include/uapi/linux/bpf_perf_event.h b/include/uapi/linux/bpf_perf_event.h
index eb1b9d21250c..cf614ddf0381 100644
--- a/include/uapi/linux/bpf_perf_event.h
+++ b/include/uapi/linux/bpf_perf_event.h
@@ -10,10 +10,16 @@
#include <asm/bpf_perf_event.h>
+#if __has_attribute(preserve_static_offset) && defined(__bpf__)
+#define __bpf_ctx __attribute__((preserve_static_offset))
+#else
+#define __bpf_ctx
+#endif
+
struct bpf_perf_event_data {
bpf_user_pt_regs_t regs;
__u64 sample_period;
__u64 addr;
-};
+} __bpf_ctx;
#endif /* _UAPI__LINUX_BPF_PERF_EVENT_H__ */
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index e0545201b55f..75eee56ed732 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
[...]
