[PATCH bpf-next v2 4/7] selftests/bpf: tests with delayed read/precision makrs in loop body

[Eduard Zingerman <eddyz87@gmail.com>]

These test cases try to hide read and precision marks from loop
convergence logic: marks would only be assigned on subsequent loop
iterations or after exploring states pushed to env->head stack first.
Without verifier fix to use exact states comparison logic for
iterators convergence these tests (except 'triple_continue') would be
errorneously marked as safe.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
 tools/testing/selftests/bpf/progs/iters.c | 443 ++++++++++++++++++++++
 1 file changed, 443 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/iters.c b/tools/testing/selftests/bpf/progs/iters.c
index 6b9b3c56f009..ee85cc6d3444 100644
--- a/tools/testing/selftests/bpf/progs/iters.c
+++ b/tools/testing/selftests/bpf/progs/iters.c
@@ -14,6 +14,13 @@ int my_pid;
 int arr[256];
 int small_arr[16] SEC(".data.small_arr");
 
+struct {
+	__uint(type, BPF_MAP_TYPE_HASH);
+	__uint(max_entries, 10);
+	__type(key, int);
+	__type(value, int);
+} amap SEC(".maps");
+
 #ifdef REAL_TEST
 #define MY_PID_GUARD() if (my_pid != (bpf_get_current_pid_tgid() >> 32)) return 0
 #else
@@ -716,4 +723,440 @@ int iter_pass_iter_ptr_to_subprog(const void *ctx)
 	return 0;
 }
 
+SEC("?raw_tp")
+__failure
+__msg("R1 type=scalar expected=fp")
+__naked int delayed_read_mark(void)
+{
+	/* This is equivalent to C program below.
+	 * The call to bpf_iter_num_next() is reachable with r7 values &fp[-16] and 0xdead.
+	 * State with r7=&fp[-16] is visited first and follows r6 != 42 ... continue branch.
+	 * At this point iterator next() call is reached with r7 that has no read mark.
+	 * Loop body with r7=0xdead would only be visited if verifier would decide to continue
+	 * with second loop iteration. Absence of read mark on r7 might affect state
+	 * equivalent logic used for iterator convergence tracking.
+	 *
+	 * r7 = &fp[-16]
+	 * fp[-16] = 0
+	 * r6 = bpf_get_prandom_u32()
+	 * bpf_iter_num_new(&fp[-8], 0, 10)
+	 * while (bpf_iter_num_next(&fp[-8])) {
+	 *   r6++
+	 *   if (r6 != 42) {
+	 *     r7 = 0xdead
+	 *     continue;
+	 *   }
+	 *   bpf_probe_read_user(r7, 8, 0xdeadbeef); // this is not safe
+	 * }
+	 * bpf_iter_num_destroy(&fp[-8])
+	 * return 0
+	 */
+	asm volatile (
+		"r7 = r10;"
+		"r7 += -16;"
+		"r0 = 0;"
+		"*(u64 *)(r7 + 0) = r0;"
+		"call %[bpf_get_prandom_u32];"
+		"r6 = r0;"
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+	"1:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto 2f;"
+		"r6 += 1;"
+		"if r6 != 42 goto 3f;"
+		"r7 = 0xdead;"
+		"goto 1b;"
+	"3:"
+		"r1 = r7;"
+		"r2 = 8;"
+		"r3 = 0xdeadbeef;"
+		"call %[bpf_probe_read_user];"
+		"goto 1b;"
+	"2:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+		:
+		: __imm(bpf_get_prandom_u32),
+		  __imm(bpf_iter_num_new),
+		  __imm(bpf_iter_num_next),
+		  __imm(bpf_iter_num_destroy),
+		  __imm(bpf_probe_read_user)
+		: __clobber_all
+	);
+}
+
+SEC("?raw_tp")
+__failure
+__msg("math between fp pointer and register with unbounded")
+__naked int delayed_precision_mark(void)
+{
+	/* This is equivalent to C program below.
+	 * The test is similar to delayed_iter_mark but verifies that incomplete
+	 * precision don't fool verifier.
+	 * The call to bpf_iter_num_next() is reachable with r7 values -16 and -32.
+	 * State with r7=-16 is visited first and follows r6 != 42 ... continue branch.
+	 * At this point iterator next() call is reached with r7 that has no read
+	 * and precision marks.
+	 * Loop body with r7=-32 would only be visited if verifier would decide to continue
+	 * with second loop iteration. Absence of precision mark on r7 might affect state
+	 * equivalent logic used for iterator convergence tracking.
+	 *
+	 * r8 = 0
+	 * fp[-16] = 0
+	 * r7 = -16
+	 * r6 = bpf_get_prandom_u32()
+	 * bpf_iter_num_new(&fp[-8], 0, 10)
+	 * while (bpf_iter_num_next(&fp[-8])) {
+	 *   if (r6 != 42) {
+	 *     r7 = -32
+	 *     r6 = bpf_get_prandom_u32()
+	 *     continue;
+	 *   }
+	 *   r0 = r10
+	 *   r0 += r7
+	 *   r8 = *(u64 *)(r0 + 0)           // this is not safe
+	 *   r6 = bpf_get_prandom_u32()
+	 * }
+	 * bpf_iter_num_destroy(&fp[-8])
+	 * return r8
+	 */
+	asm volatile (
+		"r8 = 0;"
+		"*(u64 *)(r10 - 16) = r8;"
+		"r7 = -16;"
+		"call %[bpf_get_prandom_u32];"
+		"r6 = r0;"
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+	"1:"
+		"r1 = r10;"
+		"r1 += -8;\n"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto 2f;"
+		"if r6 != 42 goto 3f;"
+		"r7 = -32;"
+		"call %[bpf_get_prandom_u32];"
+		"r6 = r0;"
+		"goto 1b;\n"
+	"3:"
+		"r0 = r10;"
+		"r0 += r7;"
+		"r8 = *(u64 *)(r0 + 0);"
+		"call %[bpf_get_prandom_u32];"
+		"r6 = r0;"
+		"goto 1b;\n"
+	"2:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = r8;"
+		"exit;"
+		:
+		: __imm(bpf_get_prandom_u32),
+		  __imm(bpf_iter_num_new),
+		  __imm(bpf_iter_num_next),
+		  __imm(bpf_iter_num_destroy),
+		  __imm(bpf_probe_read_user)
+		: __clobber_all
+	);
+}
+
+SEC("?raw_tp")
+__failure
+__msg("math between fp pointer and register with unbounded")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked int loop_state_deps1(void)
+{
+	/* This is equivalent to C program below.
+	 *
+	 * The case turns out to be tricky in a sense that:
+	 * - states with c=-25 are explored only on a second iteration
+	 *   of the outer loop;
+	 * - states with read+precise mark on c are explored only on
+	 *   second iteration of the inner loop and in a state which
+	 *   is pushed to states stack first.
+	 *
+	 * Depending on the details of iterator convergence logic
+	 * verifier might stop states traversal too early and miss
+	 * unsafe c=-25 memory access.
+	 *
+	 *   j = iter_new();		 // fp[-16]
+	 *   a = 0;			 // r6
+	 *   b = 0;			 // r7
+	 *   c = -24;			 // r8
+	 *   while (iter_next(j)) {
+	 *     i = iter_new();		 // fp[-8]
+	 *     a = 0;			 // r6
+	 *     b = 0;			 // r7
+	 *     while (iter_next(i)) {
+	 *	 if (a == 1) {
+	 *	   a = 0;
+	 *	   b = 1;
+	 *	 } else if (a == 0) {
+	 *	   a = 1;
+	 *	   if (random() == 42)
+	 *	     continue;
+	 *	   if (b == 1) {
+	 *	     *(r10 + c) = 7;  // this is not safe
+	 *	     iter_destroy(i);
+	 *	     iter_destroy(j);
+	 *	     return;
+	 *	   }
+	 *	 }
+	 *     }
+	 *     iter_destroy(i);
+	 *     a = 0;
+	 *     b = 0;
+	 *     c = -25;
+	 *   }
+	 *   iter_destroy(j);
+	 *   return;
+	 */
+	asm volatile (
+		"r1 = r10;"
+		"r1 += -16;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+		"r6 = 0;"
+		"r7 = 0;"
+		"r8 = -24;"
+	"j_loop_%=:"
+		"r1 = r10;"
+		"r1 += -16;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto j_loop_end_%=;"
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+		"r6 = 0;"
+		"r7 = 0;"
+	"i_loop_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto i_loop_end_%=;"
+	"check_one_r6_%=:"
+		"if r6 != 1 goto check_zero_r6_%=;"
+		"r6 = 0;"
+		"r7 = 1;"
+		"goto i_loop_%=;"
+	"check_zero_r6_%=:"
+		"if r6 != 0 goto i_loop_%=;"
+		"r6 = 1;"
+		"call %[bpf_get_prandom_u32];"
+		"if r0 != 42 goto check_one_r7_%=;"
+		"goto i_loop_%=;"
+	"check_one_r7_%=:"
+		"if r7 != 1 goto i_loop_%=;"
+		"r0 = r10;"
+		"r0 += r8;"
+		"r1 = 7;"
+		"*(u64 *)(r0 + 0) = r1;"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r1 = r10;"
+		"r1 += -16;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+	"i_loop_end_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r6 = 0;"
+		"r7 = 0;"
+		"r8 = -25;"
+		"goto j_loop_%=;"
+	"j_loop_end_%=:"
+		"r1 = r10;"
+		"r1 += -16;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+		:
+		: __imm(bpf_get_prandom_u32),
+		  __imm(bpf_iter_num_new),
+		  __imm(bpf_iter_num_next),
+		  __imm(bpf_iter_num_destroy)
+		: __clobber_all
+	);
+}
+
+SEC("?raw_tp")
+__success
+__naked int triple_continue(void)
+{
+	/* This is equivalent to C program below.
+	 * High branching factor of the loop body turned out to be
+	 * problematic for one of the iterator convergence tracking
+	 * algorithms explored.
+	 *
+	 * r6 = bpf_get_prandom_u32()
+	 * bpf_iter_num_new(&fp[-8], 0, 10)
+	 * while (bpf_iter_num_next(&fp[-8])) {
+	 *   if (bpf_get_prandom_u32() != 42)
+	 *     continue;
+	 *   if (bpf_get_prandom_u32() != 42)
+	 *     continue;
+	 *   if (bpf_get_prandom_u32() != 42)
+	 *     continue;
+	 *   r0 += 0;
+	 * }
+	 * bpf_iter_num_destroy(&fp[-8])
+	 * return 0
+	 */
+	asm volatile (
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+	"loop_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto loop_end_%=;"
+		"call %[bpf_get_prandom_u32];"
+		"if r0 != 42 goto loop_%=;"
+		"call %[bpf_get_prandom_u32];"
+		"if r0 != 42 goto loop_%=;"
+		"call %[bpf_get_prandom_u32];"
+		"if r0 != 42 goto loop_%=;"
+		"r0 += 0;"
+		"goto loop_%=;"
+	"loop_end_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+		:
+		: __imm(bpf_get_prandom_u32),
+		  __imm(bpf_iter_num_new),
+		  __imm(bpf_iter_num_next),
+		  __imm(bpf_iter_num_destroy)
+		: __clobber_all
+	);
+}
+
+SEC("raw_tp")
+__success
+__naked int checkpoint_states_deletion(void)
+{
+	/* This is equivalent to C program below.
+	 *
+	 *   int i;
+	 *   int sum = 0;
+	 *   bpf_for(i, 0, 10) {
+	 *     int *a = bpf_map_lookup_elem(&amap, &i);
+	 *     int *b = bpf_map_lookup_elem(&amap, &i);
+	 *     int *c = bpf_map_lookup_elem(&amap, &i);
+	 *     if (a)
+	 *             sum += 1;
+	 *     if (b)
+	 *             sum += 1;
+	 *     if (c)
+	 *             sum += 1;
+	 *     // a = NULL;
+	 *   }
+	 *   return 0;
+	 *
+	 * Note the commented out 'a = NULL;'.
+	 * The body of the loop spawns multiple simulation paths
+	 * with different combination of NULL/non-NULL information for a/b/c.
+	 * Each combination is unique from states_equal() point of view.
+	 * Explored states checkpoint is created after each iterator next call.
+	 * Iterator convergence logic expects that eventually current state
+	 * would get equal to one of the explored states and thus loop
+	 * exploration would be finished (at-least for a specific path).
+	 * Verifier evicts explored states with high miss to hit ratio
+	 * to to avoid comparing current state with too many explored
+	 * states per instruction.
+	 * This test is designed to trick the following eviction policy:
+	 *
+	 *    sl->miss_cnt > sl->hit_cnt * 3 + 3 // if true sl->state is evicted
+	 *
+	 * *If* checkpoint states are allowed to be evicted and the
+	 * policy above is used, verifier would remove states too early,
+	 * before loop convergence could be established.
+	 * Uncommenting 'a = NULL;' reduces number of distinct states
+	 * and program verifies.
+	 */
+	asm volatile (
+		"r6 = 0;"   /* a */
+		"r7 = 0;"   /* b */
+		"r8 = 0;"   /* c */
+		"r9 = 0;"   /* sum */
+		"r1 = r10;"
+		"r1 += -8;"
+		"r2 = 0;"
+		"r3 = 10;"
+		"call %[bpf_iter_num_new];"
+	"loop_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_next];"
+		"if r0 == 0 goto loop_end_%=;"
+
+		"*(u64 *)(r10 - 16) = r0;"
+
+		"r1 = %[amap] ll;"
+		"r2 = r10;"
+		"r2 += -16;"
+		"call %[bpf_map_lookup_elem];"
+		"r6 = r0;"
+
+		"r1 = %[amap] ll;"
+		"r2 = r10;"
+		"r2 += -16;"
+		"call %[bpf_map_lookup_elem];"
+		"r7 = r0;"
+
+		"r1 = %[amap] ll;"
+		"r2 = r10;"
+		"r2 += -16;"
+		"call %[bpf_map_lookup_elem];"
+		"r8 = r0;"
+
+		"if r6 == 0 goto +1;"
+		"r9 += 1;"
+		"if r7 == 0 goto +1;"
+		"r9 += 1;"
+		"if r8 == 0 goto +1;"
+		"r9 += 1;"
+
+		/* "r6 = 0;" // Commented out 'a = NULL;' */
+		"goto loop_%=;"
+	"loop_end_%=:"
+		"r1 = r10;"
+		"r1 += -8;"
+		"call %[bpf_iter_num_destroy];"
+		"r0 = 0;"
+		"exit;"
+		:
+		: __imm(bpf_map_lookup_elem),
+		  __imm(bpf_iter_num_new),
+		  __imm(bpf_iter_num_next),
+		  __imm(bpf_iter_num_destroy),
+		  __imm_addr(amap)
+		: __clobber_all
+	);
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.42.0