selftests/bpf: test if state loops are detected in a tricky case

A convoluted test case for iterators convergence logic that
demonstrates that states with branch count equal to 0 might still be
a part of not completely explored loop.

E.g. consider the following state diagram:

               initial     Here state 'succ' was processed first,
                 |         it was eventually tracked to produce a
                 V         state identical to 'hdr'.
    .---------> hdr        All branches from 'succ' had been explored
    |            |         and thus 'succ' has its .branches == 0.
    |            V
    |    .------...        Suppose states 'cur' and 'succ' correspond
    |    |       |         to the same instruction + callsites.
    |    V       V         In such case it is necessary to check
    |   ...     ...        whether 'succ' and 'cur' are identical.
    |    |       |         If 'succ' and 'cur' are a part of the same loop
    |    V       V         they have to be compared exactly.
    |   succ <- cur
    |    |
    |    V
    |   ...
    |    |
    '----'

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20231024000917.12153-7-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/testing/selftests/bpf/progs/iters.c b/tools/testing/selftests/bpf/progs/iters.c
index 764a68420c3e9ed23fc606054dda5ec45449e30b..c20c4e38b71c5b9a7db16b6519dfbdf3fea5b89b 100644 (file)
--- a/tools/testing/selftests/bpf/progs/iters.c
+++ b/tools/testing/selftests/bpf/progs/iters.c
@@ -998,6 +998,183 @@ __naked int loop_state_deps1(void)
        );
 }
 
+SEC("?raw_tp")
+__failure
+__msg("math between fp pointer and register with unbounded")
+__flag(BPF_F_TEST_STATE_FREQ)
+__naked int loop_state_deps2(void)
+{
+       /* This is equivalent to C program below.
+        *
+        * The case turns out to be tricky in a sense that:
+        * - states with read+precise mark on c are explored only on a second
+        *   iteration of the first inner loop and in a state which is pushed to
+        *   states stack first.
+        * - states with c=-25 are explored only on a second iteration of the
+        *   second 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);
+        *     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) {
+        *           a = 0;
+        *           c = -25;
+        *         }
+        *       }
+        *     }
+        *     iter_destroy(i);
+        *   }
+        *   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_%=;"
+
+               /* first inner loop */
+               "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];"
+
+               /* second inner loop */
+               "r1 = r10;"
+               "r1 += -8;"
+               "r2 = 0;"
+               "r3 = 10;"
+               "call %[bpf_iter_num_new];"
+               "r6 = 0;"
+               "r7 = 0;"
+       "i2_loop_%=:"
+               "r1 = r10;"
+               "r1 += -8;"
+               "call %[bpf_iter_num_next];"
+               "if r0 == 0 goto i2_loop_end_%=;"
+       "check2_one_r6_%=:"
+               "if r6 != 1 goto check2_zero_r6_%=;"
+               "r6 = 0;"
+               "r7 = 1;"
+               "goto i2_loop_%=;"
+       "check2_zero_r6_%=:"
+               "if r6 != 0 goto i2_loop_%=;"
+               "r6 = 1;"
+               "call %[bpf_get_prandom_u32];"
+               "if r0 != 42 goto check2_one_r7_%=;"
+               "goto i2_loop_%=;"
+       "check2_one_r7_%=:"
+               "if r7 != 1 goto i2_loop_%=;"
+               "r6 = 0;"
+               "r8 = -25;"
+               "goto i2_loop_%=;"
+       "i2_loop_end_%=:"
+               "r1 = r10;"
+               "r1 += -8;"
+               "call %[bpf_iter_num_destroy];"
+
+               "r6 = 0;"
+               "r7 = 0;"
+               "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)