sys/linux: replace id_or_fd with more precise version

The id_or_fd union was introduced before we had conditional fields to
represent IDs or fds for BPF programs or links. The union was
overapproximating those specific types.

With conditional fields, we can now use information from other fields to
determine precisely which type from the union is expected. For example,
with BPF_PROG_ATTACH, if BPF_F_ID is the only flag, then the relative_fd
field should be interpreted as a program ID.

Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>

3 files changed, 39 insertions, 31 deletions

diff --git a/sys/linux/bpf.txt b/sys/linux/bpf.txt
index c0c29dce2..dfdb83f40 100644
--- a/sys/linux/bpf.txt
+++ b/sys/linux/bpf.txt
@@ -272,9 +272,12 @@ link_create_netfilter {
 }
 
 link_create_tcx {
-	relative	id_or_fd
-	exp_revision	bpf_revision
-}
+	relative_link_fd	fd_bpf_link	(if[value[bpf_link_create_arg_t:flags] & BPF_F_LINK_OR_ID == BPF_F_LINK])
+	relative_prog_fd	fd_bpf_prog	(if[value[bpf_link_create_arg_t:flags] & BPF_F_LINK_OR_ID == 0])
+	relative_link_id	bpf_link_id	(if[value[bpf_link_create_arg_t:flags] & BPF_F_LINK_OR_ID == BPF_F_LINK_OR_ID])
+	relative_prog_id	bpf_prog_id	(if[value[bpf_link_create_arg_t:flags] & BPF_F_LINK_OR_ID == BPF_F_ID])
+	exp_revision		bpf_revision
+} [packed]
 
 link_create_uprobe_multi {
 	path		ptr64[in, filename]
@@ -287,9 +290,12 @@ link_create_uprobe_multi {
 }
 
 link_create_netkit {
-	relative	id_or_fd
-	exp_revision	bpf_revision
-}
+	relative_link_fd	fd_bpf_link	(if[value[bpf_link_create_arg_t:flags] & BPF_F_LINK_OR_ID == BPF_F_LINK])
+	relative_prog_fd	fd_bpf_prog	(if[value[bpf_link_create_arg_t:flags] & BPF_F_LINK_OR_ID == 0])
+	relative_link_id	bpf_link_id	(if[value[bpf_link_create_arg_t:flags] & BPF_F_LINK_OR_ID == BPF_F_LINK_OR_ID])
+	relative_prog_id	bpf_prog_id	(if[value[bpf_link_create_arg_t:flags] & BPF_F_LINK_OR_ID == BPF_F_ID])
+	exp_revision		bpf_revision
+} [packed]
 
 link_create_arg_extra [
 	target_btf_id	bpf_btf_id
@@ -301,7 +307,7 @@ link_create_arg_extra [
 	tcx		link_create_tcx
 	uprobe_multi	link_create_uprobe_multi
 	netkit		link_create_netkit
-]
+] [varlen]
 
 type bpf_link_create_arg_t[PROG_FD, TARGET_FD, ATTACH_TYPE, FLAGS] {
 	prog_fd		PROG_FD
@@ -396,32 +402,33 @@ bpf_attach_targets [
 	ifindex	ifindex
 ]
 
-id_or_fd [
-	link_fd	fd_bpf_link
-	prog_fd	fd_bpf_prog
-	link_id	bpf_link_id
-	prog_id	bpf_prog_id
-]
+define BPF_F_LINK_OR_ID	BPF_F_LINK | BPF_F_ID
 
 bpf_attach_arg {
-	target		bpf_attach_targets
-	attach_bpf_fd	fd_bpf_prog
-	type		flags[bpf_attach_type, int32]
-	flags		flags[bpf_attach_flags, int32]
-	replace_bpf_fd	fd_bpf_prog
-	relative_obj	id_or_fd
-	exp_revision	bpf_revision
-}
+	target			bpf_attach_targets
+	attach_bpf_fd		fd_bpf_prog
+	type			flags[bpf_attach_type, int32]
+	flags			flags[bpf_attach_flags, int32]
+	replace_bpf_fd		fd_bpf_prog
+	relative_link_fd	fd_bpf_link	(if[value[flags] & BPF_F_LINK_OR_ID == BPF_F_LINK])
+	relative_prog_fd	fd_bpf_prog	(if[value[flags] & BPF_F_LINK_OR_ID == 0])
+	relative_link_id	bpf_link_id	(if[value[flags] & BPF_F_LINK_OR_ID == BPF_F_LINK_OR_ID])
+	relative_prog_id	bpf_prog_id	(if[value[flags] & BPF_F_LINK_OR_ID == BPF_F_ID])
+	exp_revision		bpf_revision
+} [packed]
 
 bpf_detach_arg {
-	target		bpf_attach_targets
-	prog		fd_bpf_prog
-	type		flags[bpf_attach_type, int32]
-	flags		flags[bpf_mprog_attach_flags, int32]
-	replace_bpf_fd	const[0, int32]
-	relative_obj	id_or_fd
-	exp_revision	bpf_revision
-}
+	target			bpf_attach_targets
+	prog			fd_bpf_prog
+	type			flags[bpf_attach_type, int32]
+	flags			flags[bpf_mprog_attach_flags, int32]
+	replace_bpf_fd		const[0, int32]
+	relative_link_fd	fd_bpf_link	(if[value[flags] & BPF_F_LINK_OR_ID == BPF_F_LINK])
+	relative_prog_fd	fd_bpf_prog	(if[value[flags] & BPF_F_LINK_OR_ID == 0])
+	relative_link_id	bpf_link_id	(if[value[flags] & BPF_F_LINK_OR_ID == BPF_F_LINK_OR_ID])
+	relative_prog_id	bpf_prog_id	(if[value[flags] & BPF_F_LINK_OR_ID == BPF_F_ID])
+	exp_revision		bpf_revision
+} [packed]
 
 bpf_test_prog_arg {
 	prog		fd_bpf_prog
diff --git a/sys/linux/bpf.txt.const b/sys/linux/bpf.txt.const
index 3701a8177..c95f44494 100644
--- a/sys/linux/bpf.txt.const
+++ b/sys/linux/bpf.txt.const
@@ -62,6 +62,7 @@ BPF_F_ID = 32
 BPF_F_INNER_MAP = 4096
 BPF_F_KPROBE_MULTI_RETURN = 1
 BPF_F_LINK = 8192
+BPF_F_LINK_OR_ID = 8224
 BPF_F_LOCK = 4
 BPF_F_MMAPABLE = 1024
 BPF_F_NETFILTER_IP_DEFRAG = 1
diff --git a/sys/linux/test/bpf_cgroup b/sys/linux/test/bpf_cgroup
index 0c31e3442..1ec4c55a9 100644
--- a/sys/linux/test/bpf_cgroup
+++ b/sys/linux/test/bpf_cgroup
@@ -10,7 +10,7 @@ r2 = bpf$PROG_LOAD(AUTO, &AUTO={0x17, AUTO, &AUTO=@framed={{AUTO, AUTO, AUTO, AU
 
 r3 = openat(0xffffffffffffff9c, &AUTO='./cgroup\x00', 0x0, 0x0)
 
-r4 = bpf$BPF_PROG_ATTACH(AUTO, &AUTO={@cgroup=r3, r2, 0x12, 0x0, 0x0, @prog_id=0x0, 0x0}, AUTO)
+r4 = bpf$BPF_PROG_ATTACH(AUTO, &AUTO={@cgroup=r3, r2, 0x12, 0x0, 0x0, @void, @value=0x0, @void, @void, 0x0}, AUTO)
 
 # It should fail now.
 
@@ -18,7 +18,7 @@ r5 = write$tcp_congestion(r0, &AUTO='reno\x00', AUTO) # EPERM
 
 # Detach the BPF program.
 
-r6 = bpf$BPF_PROG_DETACH(AUTO, &AUTO={@cgroup=r3, r2, 0x12, 0x0, 0x0, @prog_id=0x0, 0x0}, AUTO)
+r6 = bpf$BPF_PROG_DETACH(AUTO, &AUTO={@cgroup=r3, r2, 0x12, 0x0, 0x0, @void, @value=0x0, @void, @void, 0x0}, AUTO)
 
 # It should work again.