bpf: fix regs_exact() logic in regsafe() to remap IDs correctly

Comparing IDs exactly between two separate states is not just
suboptimal, but also incorrect in some cases. So update regs_exact()
check to do byte-by-byte memcmp() only up to id/ref_obj_id. For id and
ref_obj_id perform proper check_ids() checks, taking into account idmap.

This change makes more states equivalent improving insns and states
stats across a bunch of selftest BPF programs:

File                                         Program                           Insns (A)  Insns (B)  Insns   (DIFF)  States (A)  States (B)  States (DIFF)
-------------------------------------------  --------------------------------  ---------  ---------  --------------  ----------  ----------  -------------
cgrp_kfunc_success.bpf.linked1.o             test_cgrp_get_release                   141        137     -4 (-2.84%)          13          13    +0 (+0.00%)
cgrp_kfunc_success.bpf.linked1.o             test_cgrp_xchg_release                  142        139     -3 (-2.11%)          14          13    -1 (-7.14%)
connect6_prog.bpf.linked1.o                  connect_v6_prog                         139        102   -37 (-26.62%)           9           6   -3 (-33.33%)
ima.bpf.linked1.o                            bprm_creds_for_exec                      68         61    -7 (-10.29%)           6           5   -1 (-16.67%)
linked_list.bpf.linked1.o                    global_list_in_list                     569        499   -70 (-12.30%)          60          52   -8 (-13.33%)
linked_list.bpf.linked1.o                    global_list_push_pop                    167        150   -17 (-10.18%)          18          16   -2 (-11.11%)
linked_list.bpf.linked1.o                    global_list_push_pop_multiple           881        815    -66 (-7.49%)          74          63  -11 (-14.86%)
linked_list.bpf.linked1.o                    inner_map_list_in_list                  579        534    -45 (-7.77%)          61          55    -6 (-9.84%)
linked_list.bpf.linked1.o                    inner_map_list_push_pop                 190        181     -9 (-4.74%)          19          18    -1 (-5.26%)
linked_list.bpf.linked1.o                    inner_map_list_push_pop_multiple        916        850    -66 (-7.21%)          75          64  -11 (-14.67%)
linked_list.bpf.linked1.o                    map_list_in_list                        588        525   -63 (-10.71%)          62          55   -7 (-11.29%)
linked_list.bpf.linked1.o                    map_list_push_pop                       183        174     -9 (-4.92%)          18          17    -1 (-5.56%)
linked_list.bpf.linked1.o                    map_list_push_pop_multiple              909        843    -66 (-7.26%)          75          64  -11 (-14.67%)
map_kptr.bpf.linked1.o                       test_map_kptr                           264        256     -8 (-3.03%)          26          26    +0 (+0.00%)
map_kptr.bpf.linked1.o                       test_map_kptr_ref                        95         91     -4 (-4.21%)           9           8   -1 (-11.11%)
task_kfunc_success.bpf.linked1.o             test_task_xchg_release                  139        136     -3 (-2.16%)          14          13    -1 (-7.14%)
test_bpf_nf.bpf.linked1.o                    nf_skb_ct_test                          815        509  -306 (-37.55%)          57          30  -27 (-47.37%)
test_bpf_nf.bpf.linked1.o                    nf_xdp_ct_test                          815        509  -306 (-37.55%)          57          30  -27 (-47.37%)
test_cls_redirect.bpf.linked1.o              cls_redirect                          78925      78390   -535 (-0.68%)        4782        4704   -78 (-1.63%)
test_cls_redirect_subprogs.bpf.linked1.o     cls_redirect                          64901      63897  -1004 (-1.55%)        4612        4470  -142 (-3.08%)
test_sk_lookup.bpf.linked1.o                 access_ctx_sk                           181         95   -86 (-47.51%)          19          10   -9 (-47.37%)
test_sk_lookup.bpf.linked1.o                 ctx_narrow_access                       447        437    -10 (-2.24%)          38          37    -1 (-2.63%)
test_sk_lookup_kern.bpf.linked1.o            sk_lookup_success                       148        133   -15 (-10.14%)          14          12   -2 (-14.29%)
test_tcp_check_syncookie_kern.bpf.linked1.o  check_syncookie_clsact                  304        300     -4 (-1.32%)          23          22    -1 (-4.35%)
test_tcp_check_syncookie_kern.bpf.linked1.o  check_syncookie_xdp                     304        300     -4 (-1.32%)          23          22    -1 (-4.35%)
test_verify_pkcs7_sig.bpf.linked1.o          bpf                                      87         76   -11 (-12.64%)           7           6   -1 (-14.29%)
-------------------------------------------  --------------------------------  ---------  ---------  --------------  ----------  ----------  -------------
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20221223054921.958283-7-andrii@kernel.orgSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/verifier.c

@@ -12946,6 +12946,13 @@ static bool check_ids(u32 old_id, u32 cur_id, struct bpf_id_pair *idmap)
 {
 	unsigned int i;
 
+	/* either both IDs should be set or both should be zero */
+	if (!!old_id != !!cur_id)
+		return false;
+
+	if (old_id == 0) /* cur_id == 0 as well */
+		return true;
+
 	for (i = 0; i < BPF_ID_MAP_SIZE; i++) {
 		if (!idmap[i].old) {
 			/* Reached an empty slot; haven't seen this id before */
@@ -13058,9 +13065,12 @@ static void clean_live_states(struct bpf_verifier_env *env, int insn,
 }
 
 static bool regs_exact(const struct bpf_reg_state *rold,
-		       const struct bpf_reg_state *rcur)
+		       const struct bpf_reg_state *rcur,
+		       struct bpf_id_pair *idmap)
 {
-	return memcmp(rold, rcur, offsetof(struct bpf_reg_state, parent)) == 0;
+	return memcmp(rold, rcur, offsetof(struct bpf_reg_state, id)) == 0 && 
+	       check_ids(rold->id, rcur->id, idmap) &&
+	       check_ids(rold->ref_obj_id, rcur->ref_obj_id, idmap);
 }
 
 /* Returns true if (rold safe implies rcur safe) */
@@ -13102,7 +13112,7 @@ static bool regsafe(struct bpf_verifier_env *env, struct bpf_reg_state *rold,
 
 	switch (base_type(rold->type)) {
 	case SCALAR_VALUE:
-		if (regs_exact(rold, rcur))
+		if (regs_exact(rold, rcur, idmap))
 			return true;
 		if (env->explore_alu_limits)
 			return false;
@@ -13136,7 +13146,7 @@ static bool regsafe(struct bpf_verifier_env *env, struct bpf_reg_state *rold,
 		if (rold->off != rcur->off)
 			return false;
 		/* id relations must be preserved */
-		if (rold->id && !check_ids(rold->id, rcur->id, idmap))
+		if (!check_ids(rold->id, rcur->id, idmap))
 			return false;
 		/* new val must satisfy old val knowledge */
 		return range_within(rold, rcur) &&
@@ -13145,10 +13155,9 @@ static bool regsafe(struct bpf_verifier_env *env, struct bpf_reg_state *rold,
 		/* two stack pointers are equal only if they're pointing to
 		 * the same stack frame, since fp-8 in foo != fp-8 in bar
 		 */
-		return regs_exact(rold, rcur) && rold->frameno == rcur->frameno;
+		return regs_exact(rold, rcur, idmap) && rold->frameno == rcur->frameno;
 	default:
-		/* Only valid matches are exact, which memcmp() */
-		return regs_exact(rold, rcur);
+		return regs_exact(rold, rcur, idmap);
 	}
 }