bpf: verifier: Allocate idmap scratch in verifier env

func_states_equal makes a very short lived allocation for idmap,
probably because it's too large to fit on the stack. However the
function is called quite often, leading to a lot of alloc / free
churn. Replace the temporary allocation with dedicated scratch
space in struct bpf_verifier_env.

Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Edward Cree <ecree.xilinx@gmail.com>
Link: https://lore.kernel.org/bpf/20210429134656.122225-4-lmb@cloudflare.com

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 0684151..d4632aa 100644 (file)
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -215,6 +215,13 @@ struct bpf_idx_pair {
        u32 idx;
 };
 
+struct bpf_id_pair {
+       u32 old;
+       u32 cur;
+};
+
+/* Maximum number of register states that can exist at once */
+#define BPF_ID_MAP_SIZE (MAX_BPF_REG + MAX_BPF_STACK / BPF_REG_SIZE)
 #define MAX_CALL_FRAMES 8
 struct bpf_verifier_state {
        /* call stack tracking */
@@ -418,6 +425,7 @@ struct bpf_verifier_env {
        const struct bpf_line_info *prev_linfo;
        struct bpf_verifier_log log;
        struct bpf_subprog_info subprog_info[BPF_MAX_SUBPROGS + 1];
+       struct bpf_id_pair idmap_scratch[BPF_ID_MAP_SIZE];
        struct {
                int *insn_state;
                int *insn_stack;

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 380c8ad..bdfdb54 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9748,13 +9748,6 @@ static bool range_within(struct bpf_reg_state *old,
               old->s32_max_value >= cur->s32_max_value;
 }
 
-/* Maximum number of register states that can exist at once */
-#define ID_MAP_SIZE    (MAX_BPF_REG + MAX_BPF_STACK / BPF_REG_SIZE)
-struct idpair {
-       u32 old;
-       u32 cur;
-};
-
 /* If in the old state two registers had the same id, then they need to have
  * the same id in the new state as well.  But that id could be different from
  * the old state, so we need to track the mapping from old to new ids.
@@ -9765,11 +9758,11 @@ struct idpair {
  * So we look through our idmap to see if this old id has been seen before.  If
  * so, we require the new id to match; otherwise, we add the id pair to the map.
  */
-static bool check_ids(u32 old_id, u32 cur_id, struct idpair *idmap)
+static bool check_ids(u32 old_id, u32 cur_id, struct bpf_id_pair *idmap)
 {
        unsigned int i;
 
-       for (i = 0; i < ID_MAP_SIZE; i++) {
+       for (i = 0; i < BPF_ID_MAP_SIZE; i++) {
                if (!idmap[i].old) {
                        /* Reached an empty slot; haven't seen this id before */
                        idmap[i].old = old_id;
@@ -9882,7 +9875,7 @@ next:
 
 /* Returns true if (rold safe implies rcur safe) */
 static bool regsafe(struct bpf_reg_state *rold, struct bpf_reg_state *rcur,
-                   struct idpair *idmap)
+                   struct bpf_id_pair *idmap)
 {
        bool equal;
 
@@ -10000,7 +9993,7 @@ static bool regsafe(struct bpf_reg_state *rold, struct bpf_reg_state *rcur,
 
 static bool stacksafe(struct bpf_func_state *old,
                      struct bpf_func_state *cur,
-                     struct idpair *idmap)
+                     struct bpf_id_pair *idmap)
 {
        int i, spi;
 
@@ -10097,32 +10090,23 @@ static bool refsafe(struct bpf_func_state *old, struct bpf_func_state *cur)
  * whereas register type in current state is meaningful, it means that
  * the current state will reach 'bpf_exit' instruction safely
  */
-static bool func_states_equal(struct bpf_func_state *old,
+static bool func_states_equal(struct bpf_verifier_env *env, struct bpf_func_state *old,
                              struct bpf_func_state *cur)
 {
-       struct idpair *idmap;
-       bool ret = false;
        int i;
 
-       idmap = kcalloc(ID_MAP_SIZE, sizeof(struct idpair), GFP_KERNEL);
-       /* If we failed to allocate the idmap, just say it's not safe */
-       if (!idmap)
-               return false;
-
-       for (i = 0; i < MAX_BPF_REG; i++) {
-               if (!regsafe(&old->regs[i], &cur->regs[i], idmap))
-                       goto out_free;
-       }
+       memset(env->idmap_scratch, 0, sizeof(env->idmap_scratch));
+       for (i = 0; i < MAX_BPF_REG; i++)
+               if (!regsafe(&old->regs[i], &cur->regs[i], env->idmap_scratch))
+                       return false;
 
-       if (!stacksafe(old, cur, idmap))
-               goto out_free;
+       if (!stacksafe(old, cur, env->idmap_scratch))
+               return false;
 
        if (!refsafe(old, cur))
-               goto out_free;
-       ret = true;
-out_free:
-       kfree(idmap);
-       return ret;
+               return false;
+
+       return true;
 }
 
 static bool states_equal(struct bpf_verifier_env *env,
@@ -10149,7 +10133,7 @@ static bool states_equal(struct bpf_verifier_env *env,
        for (i = 0; i <= old->curframe; i++) {
                if (old->frame[i]->callsite != cur->frame[i]->callsite)
                        return false;
-               if (!func_states_equal(old->frame[i], cur->frame[i]))
+               if (!func_states_equal(env, old->frame[i], cur->frame[i]))
                        return false;
        }
        return true;