Merge branch 'Support kernel module ksym variables'

Andrii Nakryiko says:

====================

Add support for using kernel module global variables (__ksym externs in BPF
program). BPF verifier will now support ldimm64 with src_reg=BPF_PSEUDO_BTF_ID
and non-zero insn[1].imm field, specifying module BTF's FD. In such case,
module BTF object, similarly to BPF maps referenced from ldimm64 with
src_reg=BPF_PSEUDO_MAP_FD, will be recorded in bpf_progran's auxiliary data
and refcnt will be increased for both BTF object itself and its kernel module.
This makes sure kernel module won't be unloaded from under active attached BPF
program. These refcounts will be dropped when BPF program is unloaded.

New selftest validates all this is working as intended. bpf_testmod.ko is
extended with per-CPU variable. Selftests expects the latest pahole changes
(soon to be released as v1.20) to generate per-CPU variable BTF info for
kernel module.

v2->v3:
  - added comments, addressed feedack (Yonghong, Hao);
v1->v2:
  - fixed few compiler warnings, posted as separate pre-patches;
rfc->v1:
  - use sys_membarrier(MEMBARRIER_CMD_GLOBAL) (Alexei).

Cc: Hao Luo <haoluo@google.com>
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index e941fe1484e5..dfe6f85d97dd 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -340,6 +340,7 @@ struct bpf_insn_aux_data {
 };
 
 #define MAX_USED_MAPS 64 /* max number of maps accessed by one eBPF program */
+#define MAX_USED_BTFS 64 /* max number of BTFs accessed by one BPF program */
 
 #define BPF_VERIFIER_TMP_LOG_SIZE	1024
 
@@ -398,7 +399,9 @@ struct bpf_verifier_env {
 	struct bpf_verifier_state_list **explored_states; /* search pruning optimization */
 	struct bpf_verifier_state_list *free_list;
 	struct bpf_map *used_maps[MAX_USED_MAPS]; /* array of map's used by eBPF program */
+	struct btf_mod_pair used_btfs[MAX_USED_BTFS]; /* array of BTF's used by BPF program */
 	u32 used_map_cnt;		/* number of used maps */
+	u32 used_btf_cnt;		/* number of used BTF objects */
 	u32 id_gen;			/* used to generate unique reg IDs */
 	bool allow_ptr_leaks;
 	bool allow_ptr_to_map_access;