This change prepares strobemeta for update in callbacks verification
logic. To allow bpf_loop() verification converge when multiple
callback iterations are considered:
- track offset inside strobemeta_payload->payload directly as scalar
value;
- at each iteration make sure that remaining
strobemeta_payload->payload capacity is sufficient for execution of
read_{map,str}_var functions;
- make sure that offset is tracked as unbound scalar between
iterations, otherwise verifier won't be able infer that bpf_loop
callback reaches identical states.
Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
---
.../testing/selftests/bpf/progs/strobemeta.h | 78 ++++++++++++-------
1 file changed, 48 insertions(+), 30 deletions(-)
diff --git a/tools/testing/selftests/bpf/progs/strobemeta.h b/tools/testing/selftests/bpf/progs/strobemeta.h
index e02cfd380746..40df2cc26eaf 100644
--- a/tools/testing/selftests/bpf/progs/strobemeta.h
+++ b/tools/testing/selftests/bpf/progs/strobemeta.h
@@ -24,9 +24,11 @@ struct task_struct {};
#define STACK_TABLE_EPOCH_SHIFT 20
#define STROBE_MAX_STR_LEN 1
#define STROBE_MAX_CFGS 32
+#define READ_MAP_VAR_PAYLOAD_CAP \
+ ((1 + STROBE_MAX_MAP_ENTRIES * 2) * STROBE_MAX_STR_LEN)
#define STROBE_MAX_PAYLOAD \
(STROBE_MAX_STRS * STROBE_MAX_STR_LEN + \
- STROBE_MAX_MAPS * (1 + STROBE_MAX_MAP_ENTRIES * 2) * STROBE_MAX_STR_LEN)
+ STROBE_MAX_MAPS * READ_MAP_VAR_PAYLOAD_CAP)
struct strobe_value_header {
/*
@@ -355,7 +357,7 @@ static __always_inline uint64_t read_str_var(struct strobemeta_cfg *cfg,
size_t idx, void *tls_base,
struct strobe_value_generic *value,
struct strobemeta_payload *data,
- void *payload)
+ size_t off)
{
void *location;
uint64_t len;
@@ -366,7 +368,7 @@ static __always_inline uint64_t read_str_var(struct strobemeta_cfg *cfg,
return 0;
bpf_probe_read_user(value, sizeof(struct strobe_value_generic), location);
- len = bpf_probe_read_user_str(payload, STROBE_MAX_STR_LEN, value->ptr);
+ len = bpf_probe_read_user_str(&data->payload[off], STROBE_MAX_STR_LEN, value->ptr);
/*
* if bpf_probe_read_user_str returns error (<0), due to casting to
* unsinged int, it will become big number, so next check is
@@ -378,14 +380,14 @@ static __always_inline uint64_t read_str_var(struct strobemeta_cfg *cfg,
return 0;
data->str_lens[idx] = len;
- return len;
+ return off + len;
}
-static __always_inline void *read_map_var(struct strobemeta_cfg *cfg,
- size_t idx, void *tls_base,
- struct strobe_value_generic *value,
- struct strobemeta_payload *data,
- void *payload)
+static __always_inline uint64_t read_map_var(struct strobemeta_cfg *cfg,
+ size_t idx, void *tls_base,
+ struct strobe_value_generic *value,
+ struct strobemeta_payload *data,
+ size_t off)
{
struct strobe_map_descr* descr = &data->map_descrs[idx];
struct strobe_map_raw map;
@@ -397,11 +399,11 @@ static __always_inline void *read_map_var(struct strobemeta_cfg *cfg,
location = calc_location(&cfg->map_locs[idx], tls_base);
if (!location)
- return payload;
+ return off;
bpf_probe_read_user(value, sizeof(struct strobe_value_generic), location);
if (bpf_probe_read_user(&map, sizeof(struct strobe_map_raw), value->ptr))
- return payload;
+ return off;
descr->id = map.id;
descr->cnt = map.cnt;
@@ -410,10 +412,10 @@ static __always_inline void *read_map_var(struct strobemeta_cfg *cfg,
data->req_meta_valid = 1;
}
- len = bpf_probe_read_user_str(payload, STROBE_MAX_STR_LEN, map.tag);
+ len = bpf_probe_read_user_str(&data->payload[off], STROBE_MAX_STR_LEN, map.tag);
if (len <= STROBE_MAX_STR_LEN) {
descr->tag_len = len;
- payload += len;
+ off += len;
}
#ifdef NO_UNROLL
@@ -426,22 +428,22 @@ static __always_inline void *read_map_var(struct strobemeta_cfg *cfg,
break;
descr->key_lens[i] = 0;
- len = bpf_probe_read_user_str(payload, STROBE_MAX_STR_LEN,
+ len = bpf_probe_read_user_str(&data->payload[off], STROBE_MAX_STR_LEN,
map.entries[i].key);
if (len <= STROBE_MAX_STR_LEN) {
descr->key_lens[i] = len;
- payload += len;
+ off += len;
}
descr->val_lens[i] = 0;
- len = bpf_probe_read_user_str(payload, STROBE_MAX_STR_LEN,
+ len = bpf_probe_read_user_str(&data->payload[off], STROBE_MAX_STR_LEN,
map.entries[i].val);
if (len <= STROBE_MAX_STR_LEN) {
descr->val_lens[i] = len;
- payload += len;
+ off += len;
}
}
- return payload;
+ return off;
}
#ifdef USE_BPF_LOOP
@@ -455,14 +457,20 @@ struct read_var_ctx {
struct strobemeta_payload *data;
void *tls_base;
struct strobemeta_cfg *cfg;
- void *payload;
+ size_t payload_off;
/* value gets mutated */
struct strobe_value_generic *value;
enum read_type type;
};
-static int read_var_callback(__u32 index, struct read_var_ctx *ctx)
+static int read_var_callback(__u64 index, struct read_var_ctx *ctx)
{
+ /* lose precision info for ctx->payload_off, verifier won't track
+ * double xor, barrier_var() is needed to force clang keep both xors.
+ */
+ ctx->payload_off ^= index;
+ barrier_var(ctx->payload_off);
+ ctx->payload_off ^= index;
switch (ctx->type) {
case READ_INT_VAR:
if (index >= STROBE_MAX_INTS)
@@ -472,14 +480,18 @@ static int read_var_callback(__u32 index, struct read_var_ctx *ctx)
case READ_MAP_VAR:
if (index >= STROBE_MAX_MAPS)
return 1;
- ctx->payload = read_map_var(ctx->cfg, index, ctx->tls_base,
- ctx->value, ctx->data, ctx->payload);
+ if (ctx->payload_off > sizeof(ctx->data->payload) - READ_MAP_VAR_PAYLOAD_CAP)
+ return 1;
+ ctx->payload_off = read_map_var(ctx->cfg, index, ctx->tls_base,
+ ctx->value, ctx->data, ctx->payload_off);
break;
case READ_STR_VAR:
if (index >= STROBE_MAX_STRS)
return 1;
- ctx->payload += read_str_var(ctx->cfg, index, ctx->tls_base,
- ctx->value, ctx->data, ctx->payload);
+ if (ctx->payload_off > sizeof(ctx->data->payload) - STROBE_MAX_STR_LEN)
+ return 1;
+ ctx->payload_off = read_str_var(ctx->cfg, index, ctx->tls_base,
+ ctx->value, ctx->data, ctx->payload_off);
break;
}
return 0;
@@ -501,7 +513,8 @@ static void *read_strobe_meta(struct task_struct *task,
pid_t pid = bpf_get_current_pid_tgid() >> 32;
struct strobe_value_generic value = {0};
struct strobemeta_cfg *cfg;
- void *tls_base, *payload;
+ size_t payload_off;
+ void *tls_base;
cfg = bpf_map_lookup_elem(&strobemeta_cfgs, &pid);
if (!cfg)
@@ -509,7 +522,7 @@ static void *read_strobe_meta(struct task_struct *task,
data->int_vals_set_mask = 0;
data->req_meta_valid = 0;
- payload = data->payload;
+ payload_off = 0;
/*
* we don't have struct task_struct definition, it should be:
* tls_base = (void *)task->thread.fsbase;
@@ -522,7 +535,7 @@ static void *read_strobe_meta(struct task_struct *task,
.tls_base = tls_base,
.value = &value,
.data = data,
- .payload = payload,
+ .payload_off = 0,
};
int err;
@@ -540,6 +553,11 @@ static void *read_strobe_meta(struct task_struct *task,
err = bpf_loop(STROBE_MAX_MAPS, read_var_callback, &ctx, 0);
if (err != STROBE_MAX_MAPS)
return NULL;
+
+ payload_off = ctx.payload_off;
+ /* this should not really happen, here only to satisfy verifer */
+ if (payload_off > sizeof(data->payload))
+ payload_off = sizeof(data->payload);
#else
#ifdef NO_UNROLL
#pragma clang loop unroll(disable)
@@ -555,7 +573,7 @@ static void *read_strobe_meta(struct task_struct *task,
#pragma unroll
#endif /* NO_UNROLL */
for (int i = 0; i < STROBE_MAX_STRS; ++i) {
- payload += read_str_var(cfg, i, tls_base, &value, data, payload);
+ payload_off = read_str_var(cfg, i, tls_base, &value, data, payload_off);
}
#ifdef NO_UNROLL
#pragma clang loop unroll(disable)
@@ -563,7 +581,7 @@ static void *read_strobe_meta(struct task_struct *task,
#pragma unroll
#endif /* NO_UNROLL */
for (int i = 0; i < STROBE_MAX_MAPS; ++i) {
- payload = read_map_var(cfg, i, tls_base, &value, data, payload);
+ payload_off = read_map_var(cfg, i, tls_base, &value, data, payload_off);
}
#endif /* USE_BPF_LOOP */
@@ -571,7 +589,7 @@ static void *read_strobe_meta(struct task_struct *task,
* return pointer right after end of payload, so it's possible to
* calculate exact amount of useful data that needs to be sent
*/
- return payload;
+ return &data->payload[payload_off];
}
SEC("raw_tracepoint/kfree_skb")
--
2.42.1
