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bpf/verifier: remove varlen_map_value_access flag 

The optimisation it does is broken when the 'new' register value has a
 variable offset and the 'old' was constant.  I broke it with my pointer
 types unification (see Fixes tag below), before which the 'new' value
 would have type PTR_TO_MAP_VALUE_ADJ and would thus not compare equal;
 other changes in that patch mean that its original behaviour (ignore
 min/max values) cannot be restored.
Tests on a sample set of cilium programs show no change in count of
 processed instructions.

Fixes: f1174f77b5 ("bpf/verifier: rework value tracking")
Signed-off-by: Edward Cree <ecree@solarflare.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
hifive-unleashed-5.1
Edward Cree 2017-08-23 15:10:50 +01:00 committed by David S. Miller
parent df20cb7ec1
commit 1b688a19a9
2 changed files with 12 additions and 30 deletions
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1
include/linux/bpf_verifier.h
View File

@ -125,7 +125,6 @@ struct bpf_verifier_env {
u32 id_gen; /* used to generate unique reg IDs */
bool allow_ptr_leaks;
bool seen_direct_write;
bool varlen_map_value_access;
struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */
};

41
kernel/bpf/verifier.c
View File

@ -832,11 +832,6 @@ static int check_map_access(struct bpf_verifier_env *env, u32 regno,
*/
if (log_level)
print_verifier_state(state);
/* If the offset is variable, we will need to be stricter in state
* pruning from now on.
*/
if (!tnum_is_const(reg->var_off))
env->varlen_map_value_access = true;
/* The minimum value is only important with signed
* comparisons where we can't assume the floor of a
* value is 0. If we are using signed variables for our
@ -3247,9 +3242,8 @@ static bool check_ids(u32 old_id, u32 cur_id, struct idpair *idmap)
}
/* Returns true if (rold safe implies rcur safe) */
static bool regsafe(struct bpf_reg_state *rold,
struct bpf_reg_state *rcur,
bool varlen_map_access, struct idpair *idmap)
static bool regsafe(struct bpf_reg_state *rold, struct bpf_reg_state *rcur,
struct idpair *idmap)
{
if (!(rold->live & REG_LIVE_READ))
/* explored state didn't use this */
@ -3281,22 +3275,14 @@ static bool regsafe(struct bpf_reg_state *rold,
tnum_is_unknown(rold->var_off);
}
case PTR_TO_MAP_VALUE:
if (varlen_map_access) {
/* If the new min/max/var_off satisfy the old ones and
* everything else matches, we are OK.
* We don't care about the 'id' value, because nothing
* uses it for PTR_TO_MAP_VALUE (only for ..._OR_NULL)
*/
return memcmp(rold, rcur, offsetof(struct bpf_reg_state, id)) == 0 &&
range_within(rold, rcur) &&
tnum_in(rold->var_off, rcur->var_off);
} else {
/* If the ranges/var_off were not the same, but
* everything else was and we didn't do a variable
* access into a map then we are a-ok.
*/
return memcmp(rold, rcur, offsetof(struct bpf_reg_state, id)) == 0;
}
/* If the new min/max/var_off satisfy the old ones and
* everything else matches, we are OK.
* We don't care about the 'id' value, because nothing
* uses it for PTR_TO_MAP_VALUE (only for ..._OR_NULL)
*/
return memcmp(rold, rcur, offsetof(struct bpf_reg_state, id)) == 0 &&
range_within(rold, rcur) &&
tnum_in(rold->var_off, rcur->var_off);
case PTR_TO_MAP_VALUE_OR_NULL:
/* a PTR_TO_MAP_VALUE could be safe to use as a
* PTR_TO_MAP_VALUE_OR_NULL into the same map.
@ -3380,7 +3366,6 @@ static bool states_equal(struct bpf_verifier_env *env,
struct bpf_verifier_state *old,
struct bpf_verifier_state *cur)
{
bool varlen_map_access = env->varlen_map_value_access;
struct idpair *idmap;
bool ret = false;
int i;
@ -3391,8 +3376,7 @@ static bool states_equal(struct bpf_verifier_env *env,
return false;
for (i = 0; i < MAX_BPF_REG; i++) {
if (!regsafe(&old->regs[i], &cur->regs[i], varlen_map_access,
idmap))
if (!regsafe(&old->regs[i], &cur->regs[i], idmap))
goto out_free;
}
@ -3412,7 +3396,7 @@ static bool states_equal(struct bpf_verifier_env *env,
continue;
if (!regsafe(&old->spilled_regs[i / BPF_REG_SIZE],
&cur->spilled_regs[i / BPF_REG_SIZE],
varlen_map_access, idmap))
idmap))
/* when explored and current stack slot are both storing
* spilled registers, check that stored pointers types
* are the same as well.
@ -3555,7 +3539,6 @@ static int do_check(struct bpf_verifier_env *env)
init_reg_state(regs);
state->parent = NULL;
insn_idx = 0;
env->varlen_map_value_access = false;
for (;;) {
struct bpf_insn *insn;
u8 class;