A test case to verify that variable offset BPF_ST instruction
preserves STACK_ZERO marks when writes zeros, e.g. in the following
situation:
*(u64*)(r10 - 8) = 0 ; STACK_ZERO marks for fp[-8]
r0 = random(-7, -1) ; some random number in range of [-7, -1]
r0 += r10 ; r0 is now variable offset pointer to stack
*(u8*)(r0) = 0 ; BPF_ST writing zero, STACK_ZERO mark for
; fp[-8] should be preserved.
Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
---
.../selftests/bpf/verifier/bpf_st_mem.c | 30 +++++++++++++++++++
1 file changed, 30 insertions(+)
diff --git a/tools/testing/selftests/bpf/verifier/bpf_st_mem.c b/tools/testing/selftests/bpf/verifier/bpf_st_mem.c
index 932903f9e585..3af2501082b2 100644
--- a/tools/testing/selftests/bpf/verifier/bpf_st_mem.c
+++ b/tools/testing/selftests/bpf/verifier/bpf_st_mem.c
@@ -35,3 +35,33 @@
.expected_attach_type = BPF_SK_LOOKUP,
.runs = -1,
},
+{
+ "BPF_ST_MEM stack imm zero, variable offset",
+ .insns = {
+ /* set fp[-16], fp[-24] to zeros */
+ BPF_ST_MEM(BPF_DW, BPF_REG_10, -16, 0),
+ BPF_ST_MEM(BPF_DW, BPF_REG_10, -24, 0),
+ /* r0 = random value in range [-32, -15] */
+ BPF_EMIT_CALL(BPF_FUNC_get_prandom_u32),
+ BPF_JMP_IMM(BPF_JLE, BPF_REG_0, 16, 2),
+ BPF_MOV64_IMM(BPF_REG_0, 0),
+ BPF_EXIT_INSN(),
+ BPF_ALU64_IMM(BPF_SUB, BPF_REG_0, 32),
+ /* fp[r0] = 0, make a variable offset write of zero,
+ * this should preserve zero marks on stack.
+ */
+ BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_10),
+ BPF_ST_MEM(BPF_B, BPF_REG_0, 0, 0),
+ /* r0 = fp[-20], if variable offset write was tracked correctly
+ * r0 would be a known zero.
+ */
+ BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_10, -20),
+ /* Would fail return code verification if r0 range is not tracked correctly. */
+ BPF_EXIT_INSN(),
+ },
+ .result = ACCEPT,
+ /* Use prog type that requires return value in range [0, 1] */
+ .prog_type = BPF_PROG_TYPE_SK_LOOKUP,
+ .expected_attach_type = BPF_SK_LOOKUP,
+ .runs = -1,
+},
--
2.39.1
