From c6ff14f1cd9e9b7d5631882ff509fbc29e90cfe0 Mon Sep 17 00:00:00 2001 From: Eduard Zingerman Date: Thu, 27 Aug 2026 15:48:24 -0700 Subject: [PATCH] selftests/bpf: half-dead scalar zero stack spill test A test case demonstrating unsafe pruning when spill of a scalar zero spilled on a first pass in replaced by STACK_ZERO in the __clean_func_state(). Signed-off-by: Eduard Zingerman Link: https://lore.kernel.org/r/20260827-bug-011-cleanfunc-stack-zero-simple-v1-v1-2-c0e996589a52@gmail.com Signed-off-by: Alexei Starovoitov --- .../selftests/bpf/progs/verifier_spill_fill.c | 40 +++++++++++++++++++ 1 file changed, 40 insertions(+) diff --git a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c index 8b166c42c4e0..39a1766dae3f 100644 --- a/tools/testing/selftests/bpf/progs/verifier_spill_fill.c +++ b/tools/testing/selftests/bpf/progs/verifier_spill_fill.c @@ -1403,6 +1403,46 @@ __naked void partial_fill_from_cleaned_pointer_spill(void) ::: __clobber_all); } +SEC("raw_tp") +__failure +__msg("access may be outside object bounds") +__flag(BPF_F_TEST_STATE_FREQ) +__naked void imprecise_scalar_spill_half_dead(void) +{ + asm volatile ( + /* + * Fork two paths: the one explored first spills an imprecise zero, + * the one explored second, an imprecise non-zero scalar. + */ + "call %[bpf_get_prandom_u32];" + "if r0 > 42 goto 1f;" + "r6 = 0;" + "goto 2f;" +"1:" + /* causes out of bounds access on a second path. */ + "r6 = 100500;" +"2:" + /* Force a checkpoint before the spill. */ + "goto +0;" + "*(u64 *)(r10 - 8) = r6;" + /* + * Force stack cleanup, only the low half of the spill is alive, + * so the dead high half is degraded to raw stack bytes. + * Buggy verifier converted it to STACK_ZERO w/o proper precision propagation. + */ + "goto +0;" + "r7 = *(u32 *)(r10 - 4);" + /* Use r7 as an offset into a one-byte buffer. */ + "r1 = %[single_byte_buf] ll;" + "r1 += r7;" + "r0 = *(u8 *)(r1 + 0);" + "exit;" +: +: __imm(bpf_get_prandom_u32), + __imm_addr(single_byte_buf) +: __clobber_all); +} + /* check valid spill/fill, ptr to tp buffer */ SEC("raw_tracepoint.w") __success