[PATCH v2 net-next 3/6] bpf: perf_event progs should only use preallocated maps

[Alexei Starovoitov]

Make sure that BPF_PROG_TYPE_PERF_EVENT programs only use
preallocated hash maps, since doing memory allocation
in overflow_handler can crash depending on where nmi got triggered.

Signed-off-by: Alexei Starovoitov <a...@kernel.org>
Acked-by: Daniel Borkmann <dan...@iogearbox.net>
---
 kernel/bpf/verifier.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c1c9e441f0f5..48c2705db22c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2511,6 +2511,20 @@ process_bpf_exit:
        return 0;
 }
 
+static int check_map_prog_compatibility(struct bpf_map *map,
+                                       struct bpf_prog *prog)
+
+{
+       if (prog->type == BPF_PROG_TYPE_PERF_EVENT &&
+           (map->map_type == BPF_MAP_TYPE_HASH ||
+            map->map_type == BPF_MAP_TYPE_PERCPU_HASH) &&
+           (map->map_flags & BPF_F_NO_PREALLOC)) {
+               verbose("perf_event programs can only use preallocated hash 
map\n");
+               return -EINVAL;
+       }
+       return 0;
+}
+
 /* look for pseudo eBPF instructions that access map FDs and
  * replace them with actual map pointers
  */
@@ -2518,7 +2532,7 @@ static int replace_map_fd_with_map_ptr(struct 
verifier_env *env)
 {
        struct bpf_insn *insn = env->prog->insnsi;
        int insn_cnt = env->prog->len;
-       int i, j;
+       int i, j, err;
 
        for (i = 0; i < insn_cnt; i++, insn++) {
                if (BPF_CLASS(insn->code) == BPF_LDX &&
@@ -2562,6 +2576,12 @@ static int replace_map_fd_with_map_ptr(struct 
verifier_env *env)
                                return PTR_ERR(map);
                        }
 
+                       err = check_map_prog_compatibility(map, env->prog);
+                       if (err) {
+                               fdput(f);
+                               return err;
+                       }
+
                        /* store map pointer inside BPF_LD_IMM64 instruction */
                        insn[0].imm = (u32) (unsigned long) map;
                        insn[1].imm = ((u64) (unsigned long) map) >> 32;
-- 
2.8.0