test(fspy): retry Chromium zygote handshake

Co-authored-by: GPT-5 Codex <codex@openai.com>

Author: wan9chi

.github/workflows/fspy-sigsys-research.yml

@@ -141,7 +141,7 @@ jobs:
           observer_pid=$!
 
           set +e
-          FSPY_MINIMAL_FILTER=true VITEST_CHROMIUM_SANDBOX=true \
+          VITEST_CHROMIUM_SANDBOX=true \
             DEBUG=vitest:browser:playwright,pw:browser \
             timeout 120s "$injector" "$vitest" run \
             2>&1 | tee "$probe_dir/bridge.log"

research/ptrace-exec-prototype/recursive_injector.c

@@ -153,13 +153,33 @@ __asm__(
     "  mov (%r13,%rcx), %rsi\n"
     "  mov fspy_recursive_slot_rdx(%rip), %rcx\n"
     "  mov (%r13,%rcx), %rdx\n"
+    "  mov 40(%rsi), %r8\n" /* preserve msghdr.msg_controllen */
+    "  xor %r10d, %r10d\n"  /* one zero-length record may be skipped */
+    ".Lfspy_recvmsg_retry:\n"
     "  mov fspy_recursive_slot_magic(%rip), %r9\n"
     "  mov $47, %eax\n" /* __NR_recvmsg */
     "  syscall\n"
     "  mov %rax, %r15\n"
     "  test %rax, %rax\n"
     "  js .Lfspy_recvmsg_error\n"
-    "  jz .Lfspy_recvmsg_eof\n"
+    "  jnz .Lfspy_recvmsg_positive\n"
+    "  test %r10d, %r10d\n"
+    "  jnz .Lfspy_recvmsg_eof\n"
+    "  mov $1, %r10d\n"
+    "  mov %r8, 40(%rsi)\n"
+    "  lea .Lfspy_recvmsg_retry_message(%rip), %rsi\n"
+    "  mov $34, %edx\n"
+    "  mov $2, %edi\n"
+    "  mov $1, %eax\n" /* __NR_write */
+    "  syscall\n"
+    "  mov fspy_recursive_slot_rsi(%rip), %rcx\n"
+    "  mov (%r13,%rcx), %rsi\n"
+    "  mov fspy_recursive_slot_rdi(%rip), %rcx\n"
+    "  mov (%r13,%rcx), %rdi\n"
+    "  mov fspy_recursive_slot_rdx(%rip), %rcx\n"
+    "  mov (%r13,%rcx), %rdx\n"
+    "  jmp .Lfspy_recvmsg_retry\n"
+    ".Lfspy_recvmsg_positive:\n"
     "  lea .Lfspy_recvmsg_positive_message(%rip), %rsi\n"
     "  mov $32, %edx\n"
     "  jmp .Lfspy_recvmsg_log\n"
@@ -390,6 +410,7 @@ __asm__(
     ".Lfspy_recvmsg_error_message: .ascii \"fspy: recvmsg returned error\\n\"\n"
     ".Lfspy_recvmsg_eintr_message: .ascii \"fspy: recvmsg returned EINTR\\n\"\n"
     ".Lfspy_recvmsg_enoent_message: .ascii \"fspy: recvmsg returned ENOENT\\n\"\n"
+    ".Lfspy_recvmsg_retry_message: .ascii \"fspy: recvmsg skipped zero record\\n\"\n"
     ".balign 8\n"
     "fspy_recursive_slot_rax: .quad 0\n"
     "fspy_recursive_slot_rdi: .quad 0\n"
@@ -589,6 +610,7 @@ static void install_filter(void)
         FILTER_GATEWAY_BLOCK(SYS_execve, FILTER_TAG),
         FILTER_GATEWAY_BLOCK(SYS_execveat, FILTER_TAG),
         FILTER_GATEWAY_BLOCK(SYS_rt_sigaction, FILTER_TAG),
+        FILTER_GATEWAY_BLOCK(SYS_rt_sigprocmask, FILTER_TAG),
         BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW),
     };
     const bool minimal = getenv("FSPY_MINIMAL_FILTER") != NULL;