Handle PR_SET_USER_SYSCALL_DISPATCH by emulating a kernel that doesn't support it.

Fixes #4064

Author: khuey

CMakeLists.txt

@@ -1278,6 +1278,7 @@ set(BASIC_TESTS
   prctl_name
   prctl_short_name
   prctl_speculation_ctrl
+  prctl_syscall_user_dispatch
   privileged_net_ioctl
   proc_fds
   proc_mem

src/kernel_supplement.h

@@ -547,6 +547,11 @@ enum {
 #define MREMAP_DONTUNMAP 4
 #endif
 
+// New in the 5.11 kernel
+#ifndef PR_SET_SYSCALL_USER_DISPATCH
+#define PR_SET_SYSCALL_USER_DISPATCH 59
+#endif
+
 // New in the 5.13 kernel
 #ifndef OTPERASE
 #define OTPERASE _IOW('M', 25, struct otp_info)

src/record_syscall.cc

@@ -4936,6 +4936,16 @@ static Switchable rec_prepare_syscall_arch(RecordTask* t,
           break;
         }
 
+        case PR_SET_SYSCALL_USER_DISPATCH: {
+          // Prevent any PR_SET_SYSCALL_USER_DISPATCH call and pretend it's not
+          // supported.
+          Registers r = regs;
+          r.set_arg1(intptr_t(-1));
+          t->set_regs(r);
+          syscall_state.emulate_result(-EINVAL);
+          break;
+        }
+
         default:
           syscall_state.expect_errno = EINVAL;
           break;

src/test/prctl_syscall_user_dispatch.c

@@ -0,0 +1,31 @@
+/* -*- Mode: C; tab-width: 8; c-basic-offset: 2; indent-tabs-mode: nil; -*- */
+
+#include "util.h"
+
+static int8_t control = SYSCALL_DISPATCH_FILTER_BLOCK;
+
+static void handler(int sig, siginfo_t* si, void*) {
+  control = SYSCALL_DISPATCH_FILTER_ALLOW;
+  test_assert(sig == SIGSYS);
+  test_assert(si->si_code == SYS_USER_DISPATCH);
+  atomic_puts("Not running under rr apparently");
+}
+
+int main(void) {
+  struct sigaction sa;
+
+  sa.sa_sigaction = handler;
+  sigemptyset(&sa.sa_mask);
+  sa.sa_flags = SA_SIGINFO;
+  sigaction(SIGSYS, &sa, NULL);
+
+  int ret = prctl(PR_SET_SYSCALL_USER_DISPATCH, PR_SYS_DISPATCH_ON, 0, 0, &control);
+  if (ret == -1 && errno == EINVAL) {
+    atomic_puts("PR_SET_SYSCALL_USER_DISPATCH not supported, skipping test");
+    atomic_puts("EXIT-SUCCESS");
+    return 0;
+  }
+  test_assert(ret >= 0);
+  atomic_puts("EXIT-SUCCESS");
+  return 0;
+}

src/test/util.h

@@ -563,6 +563,21 @@ struct rr_open_how {
 #ifndef PR_GET_AUXV
 #define PR_GET_AUXV 0x41555856
 #endif
+#ifndef PR_SET_SYSCALL_USER_DISPATCH
+#define PR_SET_SYSCALL_USER_DISPATCH 59
+#endif
+#ifndef PR_SYS_DISPATCH_ON
+#define PR_SYS_DISPATCH_ON 1
+#endif
+#ifndef SYSCALL_DISPATCH_FILTER_ALLOW
+#define SYSCALL_DISPATCH_FILTER_ALLOW 0
+#endif
+#ifndef SYSCALL_DISPATCH_FILTER_BLOCK
+#define SYSCALL_DISPATCH_FILTER_BLOCK 1
+#endif
+#ifndef SYS_USER_DISPATCH
+#define SYS_USER_DISPATCH 2
+#endif
 
 #ifndef BLKGETDISKSEQ
 #define BLKGETDISKSEQ _IOR(0x12,128,__u64)