[PATCH 5.13 094/104] bpf: verifier: Allocate idmap scratch in verifier env

Greg Kroah-Hartman
2021-08-02T14:16:23Z

From: Lorenz Bauer <lmb@cloudflare.com>

commit c9e73e3d2b1eb1ea7ff068e05007eec3bd8ef1c9 upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/bpf_verifier.h | 8 +++++++
kernel/bpf/verifier.c | 46 ++++++++++++++-----------------------------
2 files changed, 23 insertions(+), 31 deletions(-)

--- 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;
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9779,13 +9779,6 @@ static bool range_within(struct bpf_reg_
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.
@@ -9796,11 +9789,11 @@ 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;
@@ -9913,7 +9906,7 @@ 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;

@@ -10031,7 +10024,7 @@ static bool regsafe(struct bpf_reg_state

static bool stacksafe(struct bpf_func_state *old,
struct bpf_func_state *cur,
- struct idpair *idmap)
+ struct bpf_id_pair *idmap)
{
int i, spi;

@@ -10128,32 +10121,23 @@ static bool refsafe(struct bpf_func_stat
* 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,
@@ -10180,7 +10164,7 @@ static bool states_equal(struct bpf_veri
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;