From 5c19e1d05e9e71b42d8e779f41959254239709da Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Sat, 2 Dec 2023 09:57:04 -0800 Subject: [PATCH] selftests/bpf: adjust global_func15 test to validate prog exit precision Add one more subtest to global_func15 selftest to validate that verifier properly marks r0 as precise and avoids erroneous state pruning of the branch that has return value outside of expected [0, 1] value. Acked-by: Eduard Zingerman Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/r/20231202175705.885270-11-andrii@kernel.org Signed-off-by: Alexei Starovoitov --- .../selftests/bpf/progs/test_global_func15.c | 32 +++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/test_global_func15.c b/tools/testing/selftests/bpf/progs/test_global_func15.c index f80207480e8ad..b4e089d6981da 100644 --- a/tools/testing/selftests/bpf/progs/test_global_func15.c +++ b/tools/testing/selftests/bpf/progs/test_global_func15.c @@ -22,3 +22,35 @@ int global_func15(struct __sk_buff *skb) return v; } + +SEC("cgroup_skb/ingress") +__log_level(2) __flag(BPF_F_TEST_STATE_FREQ) +__failure +/* check that fallthrough code path marks r0 as precise */ +__msg("mark_precise: frame0: regs=r0 stack= before 2: (b7) r0 = 1") +/* check that branch code path marks r0 as precise */ +__msg("mark_precise: frame0: regs=r0 stack= before 0: (85) call bpf_get_prandom_u32#7") +__msg("At program exit the register R0 has ") +__naked int global_func15_tricky_pruning(void) +{ + asm volatile ( + "call %[bpf_get_prandom_u32];" + "if r0 s> 1000 goto 1f;" + "r0 = 1;" + "1:" + "goto +0;" /* checkpoint */ + /* cgroup_skb/ingress program is expected to return [0, 1] + * values, so branch above makes sure that in a fallthrough + * case we have a valid 1 stored in R0 register, but in + * a branch case we assign some random value to R0. So if + * there is something wrong with precision tracking for R0 at + * program exit, we might erronenously prune branch case, + * because R0 in fallthrough case is imprecise (and thus any + * value is valid from POV of verifier is_state_equal() logic) + */ + "exit;" + : + : __imm(bpf_get_prandom_u32) + : __clobber_common + ); +}