[PATCH bpf-next 2/2] selftests/bpf: Add load-acquire test for dst_reg == src_reg from ctx

Add a verifier test that a load-acquire fetching into its own source
register (dst_reg == src_reg) from a ctx pointer is rejected.

  # LDLIBS=-static PKG_CONFIG='pkg-config --static' ./vmtest.sh -- ./test_progs -t verifier_load_acquire
  [...]
  #614/1   verifier_load_acquire/load-acquire, 8-bit:OK
  #614/2   verifier_load_acquire/load-acquire, 8-bit @unpriv:OK
  #614/3   verifier_load_acquire/load-acquire, 16-bit:OK
  #614/4   verifier_load_acquire/load-acquire, 16-bit @unpriv:OK
  #614/5   verifier_load_acquire/load-acquire, 32-bit:OK
  #614/6   verifier_load_acquire/load-acquire, 32-bit @unpriv:OK
  #614/7   verifier_load_acquire/load-acquire, 64-bit:OK
  #614/8   verifier_load_acquire/load-acquire, 64-bit @unpriv:OK
  #614/9   verifier_load_acquire/load-acquire with uninitialized src_reg:OK
  #614/10  verifier_load_acquire/load-acquire with uninitialized src_reg @unpriv:OK
  #614/11  verifier_load_acquire/load-acquire with non-pointer src_reg:OK
  #614/12  verifier_load_acquire/load-acquire with non-pointer src_reg @unpriv:OK
  #614/13  verifier_load_acquire/misaligned load-acquire:OK
  #614/14  verifier_load_acquire/misaligned load-acquire @unpriv:OK
  #614/15  verifier_load_acquire/load-acquire from ctx pointer:OK
  #614/16  verifier_load_acquire/load-acquire from ctx pointer @unpriv:OK
  #614/17  verifier_load_acquire/load-acquire from ctx pointer, same dst and src register:OK
  #614/18  verifier_load_acquire/load-acquire from ctx pointer, same dst and src register @unpriv:OK
  #614/19  verifier_load_acquire/load-acquire with invalid register R15:OK
  #614/20  verifier_load_acquire/load-acquire with invalid register R15 @unpriv:OK
  #614/21  verifier_load_acquire/load-acquire from pkt pointer:OK
  #614/22  verifier_load_acquire/load-acquire from flow_keys pointer:OK
  #614/23  verifier_load_acquire/load-acquire from sock pointer:OK
  #614     verifier_load_acquire:OK
  Summary: 1/23 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Daniel Borkmann <[email protected]>
---
 .../selftests/bpf/progs/verifier_load_acquire.c  | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_load_acquire.c b/tools/testing/selftests/bpf/progs/verifier_load_acquire.c
index 74f4f19c10b8..ae1dab1b0cbb 100644
--- a/tools/testing/selftests/bpf/progs/verifier_load_acquire.c
+++ b/tools/testing/selftests/bpf/progs/verifier_load_acquire.c
@@ -148,6 +148,22 @@ __naked void load_acquire_from_ctx_pointer(void)
 	: __clobber_all);
 }
 
+SEC("socket")
+__description("load-acquire from ctx pointer, same dst and src register")
+__failure __failure_unpriv __msg("BPF_ATOMIC loads from R6 ctx is not allowed")
+__naked void load_acquire_ctx_same_dst_src(void)
+{
+	asm volatile (
+	"r6 = r1;"
+	".8byte %[load_acquire_insn];"	// w6 = load_acquire((u32 *)(r6 + 0));
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm_insn(load_acquire_insn,
+		     BPF_ATOMIC_OP(BPF_W, BPF_LOAD_ACQ, BPF_REG_6, BPF_REG_6, 0))
+	: __clobber_all);
+}
+
 SEC("xdp")
 __description("load-acquire from pkt pointer")
 __failure __msg("BPF_ATOMIC loads from R2 pkt is not allowed")
-- 
2.43.0