[PATCH bpf-next 4/4] selftests/bpf: Add tests for ld_{abs,ind} failure path in subprogs

[Daniel Borkmann <daniel@iogearbox.net>]

Extend the verifier_ld_ind BPF selftests with subprogs containing
ld_{abs,ind} and craft the test in a way where the invalid register
read is rejected in the fixed case. Also add a success case each,
and add additional coverage related to the BTF return type enforcement.

  # LDLIBS=-static PKG_CONFIG='pkg-config --static' ./vmtest.sh -- ./test_progs -t verifier_ld_ind
  [...]
  #611/1   verifier_ld_ind/ld_ind: check calling conv, r1:OK
  #611/2   verifier_ld_ind/ld_ind: check calling conv, r1 @unpriv:OK
  #611/3   verifier_ld_ind/ld_ind: check calling conv, r2:OK
  #611/4   verifier_ld_ind/ld_ind: check calling conv, r2 @unpriv:OK
  #611/5   verifier_ld_ind/ld_ind: check calling conv, r3:OK
  #611/6   verifier_ld_ind/ld_ind: check calling conv, r3 @unpriv:OK
  #611/7   verifier_ld_ind/ld_ind: check calling conv, r4:OK
  #611/8   verifier_ld_ind/ld_ind: check calling conv, r4 @unpriv:OK
  #611/9   verifier_ld_ind/ld_ind: check calling conv, r5:OK
  #611/10  verifier_ld_ind/ld_ind: check calling conv, r5 @unpriv:OK
  #611/11  verifier_ld_ind/ld_ind: check calling conv, r7:OK
  #611/12  verifier_ld_ind/ld_ind: check calling conv, r7 @unpriv:OK
  #611/13  verifier_ld_ind/ld_abs: subprog early exit on ld_abs failure:OK
  #611/14  verifier_ld_ind/ld_ind: subprog early exit on ld_ind failure:OK
  #611/15  verifier_ld_ind/ld_abs: subprog with both paths safe:OK
  #611/16  verifier_ld_ind/ld_ind: subprog with both paths safe:OK
  #611/17  verifier_ld_ind/ld_abs: reject void return subprog:OK
  #611/18  verifier_ld_ind/ld_ind: reject void return subprog:OK
  #611     verifier_ld_ind:OK
  Summary: 1/18 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 .../selftests/bpf/progs/verifier_ld_ind.c     | 142 ++++++++++++++++++
 1 file changed, 142 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_ld_ind.c b/tools/testing/selftests/bpf/progs/verifier_ld_ind.c
index c925ba9a2e74..09e81b99eecb 100644
--- a/tools/testing/selftests/bpf/progs/verifier_ld_ind.c
+++ b/tools/testing/selftests/bpf/progs/verifier_ld_ind.c
@@ -107,4 +107,146 @@ __naked void ind_check_calling_conv_r7(void)
 	: __clobber_all);
 }
 
+/*
+ * ld_{abs,ind} subprog that always sets r0=1 on the success path.
+ * bpf_gen_ld_abs() emits a hidden exit with r0=0 when the load helper
+ * fails. The verifier must model this failure return so that callers
+ * account for r0=0 as a possible return value.
+ */
+__naked __noinline __used
+static int ldabs_subprog(void)
+{
+	asm volatile (
+	"r6 = r1;"
+	".8byte %[ld_abs];"
+	"r0 = 1;"
+	"exit;"
+	:
+	: __imm_insn(ld_abs, BPF_LD_ABS(BPF_W, 0))
+	: __clobber_all);
+}
+
+__naked __noinline __used
+static int ldind_subprog(void)
+{
+	asm volatile (
+	"r6 = r1;"
+	"r7 = 0;"
+	".8byte %[ld_ind];"
+	"r0 = 1;"
+	"exit;"
+	:
+	: __imm_insn(ld_ind, BPF_LD_IND(BPF_W, BPF_REG_7, 0))
+	: __clobber_all);
+}
+
+SEC("socket")
+__description("ld_abs: subprog early exit on ld_abs failure")
+__failure __msg("R9 !read_ok")
+__naked void ld_abs_subprog_early_exit(void)
+{
+	asm volatile (
+	"call ldabs_subprog;"
+	"if r0 != 0 goto l_exit_%=;"
+	"r0 = r9;"
+	"l_exit_%=:"
+	"r0 = 0;"
+	"exit;"
+	::: __clobber_all);
+}
+
+SEC("socket")
+__description("ld_ind: subprog early exit on ld_ind failure")
+__failure __msg("R9 !read_ok")
+__naked void ld_ind_subprog_early_exit(void)
+{
+	asm volatile (
+	"call ldind_subprog;"
+	"if r0 != 0 goto l_exit_%=;"
+	"r0 = r9;"
+	"l_exit_%=:"
+	"r0 = 0;"
+	"exit;"
+	::: __clobber_all);
+}
+
+SEC("socket")
+__description("ld_abs: subprog with both paths safe")
+__success
+__naked void ld_abs_subprog_both_paths_safe(void)
+{
+	asm volatile (
+	"call ldabs_subprog;"
+	"r0 = 0;"
+	"exit;"
+	::: __clobber_all);
+}
+
+SEC("socket")
+__description("ld_ind: subprog with both paths safe")
+__success
+__naked void ld_ind_subprog_both_paths_safe(void)
+{
+	asm volatile (
+	"call ldind_subprog;"
+	"r0 = 0;"
+	"exit;"
+	::: __clobber_all);
+}
+
+/*
+ * ld_{abs,ind} in subprogs require scalar (int) return type in BTF.
+ * A test with void return must be rejected.
+ */
+__naked __noinline __used
+static void ldabs_void_subprog(void)
+{
+	asm volatile (
+	"r6 = r1;"
+	".8byte %[ld_abs];"
+	"r0 = 1;"
+	"exit;"
+	:
+	: __imm_insn(ld_abs, BPF_LD_ABS(BPF_W, 0))
+	: __clobber_all);
+}
+
+SEC("socket")
+__description("ld_abs: reject void return subprog")
+__failure __msg("LD_ABS is only allowed in functions that return 'int'")
+__naked void ld_abs_void_subprog_reject(void)
+{
+	asm volatile (
+	"call ldabs_void_subprog;"
+	"r0 = 0;"
+	"exit;"
+	::: __clobber_all);
+}
+
+__naked __noinline __used
+static void ldind_void_subprog(void)
+{
+	asm volatile (
+	"r6 = r1;"
+	"r7 = 0;"
+	".8byte %[ld_ind];"
+	"r0 = 1;"
+	"exit;"
+	:
+	: __imm_insn(ld_ind, BPF_LD_IND(BPF_W, BPF_REG_7, 0))
+	: __clobber_all);
+}
+
+SEC("socket")
+__description("ld_ind: reject void return subprog")
+__failure __msg("LD_ABS is only allowed in functions that return 'int'")
+__naked void ld_ind_void_subprog_reject(void)
+{
+	asm volatile (
+	"call ldind_void_subprog;"
+	"r0 = 0;"
+	"exit;"
+	::: __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.43.0