Re: [PATCH] linux-user: implement execveat

[Laurent Vivier]

Le 31/10/2022 à 09:40, Drew DeVault a écrit :
References: https://gitlab.com/qemu-project/qemu/-/issues/1007
Signed-off-by: Drew DeVault <s...@cmpwn.com>
---
  linux-user/syscall.c | 50 ++++++++++++++++++++++++++++++++++++++------
  1 file changed, 44 insertions(+), 6 deletions(-)
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index f55cdebee5..795f7ce4cd 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -634,6 +634,10 @@ safe_syscall4(pid_t, wait4, pid_t, pid, int *, status, 
int, options, \
  safe_syscall5(int, waitid, idtype_t, idtype, id_t, id, siginfo_t *, infop, \
                int, options, struct rusage *, rusage)
  safe_syscall3(int, execve, const char *, filename, char **, argv, char **, 
envp)
+#if defined(TARGET_NR_execveat)
+safe_syscall5(int, execveat, int, dirfd, const char *, filename,
+        char **, argv, char **, envp, int, flags)
+#endif
  #if defined(TARGET_NR_select) || defined(TARGET_NR__newselect) || \
      defined(TARGET_NR_pselect6) || defined(TARGET_NR_pselect6_time64)
  safe_syscall6(int, pselect6, int, nfds, fd_set *, readfds, fd_set *, 
writefds, \
@@ -8748,19 +8752,45 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int 
num, abi_long arg1,
          ret = get_errno(unlinkat(arg1, p, arg3));
          unlock_user(p, arg2, 0);
          return ret;
+#endif
+#if defined(TARGET_NR_execveat)
+    case TARGET_NR_execveat:
  #endif
      case TARGET_NR_execve:
          {
              char **argp, **envp;
-            int argc, envc;
+            int argc, envc, dirfd, flags;
              abi_ulong gp;
              abi_ulong guest_argp;
              abi_ulong guest_envp;
              abi_ulong addr;
+            abi_long path;
              char **q;
  
              argc = 0;
-            guest_argp = arg2;
+
+            switch (num) {
+            case TARGET_NR_execve:
+                path = arg1;
+                guest_argp = arg2;
+                guest_envp = arg3;
+                dirfd = AT_FDCWD;
+                flags = 0;
+                break;
+#if defined(TARGET_NR_execveat)
+            case TARGET_NR_execveat:
+                dirfd = arg1;
+                path = arg2;
+                guest_argp = arg3;
+                guest_envp = arg4;
+                flags = arg5;
+                break;
+#endif
+            default:
+                // squelch uninitialized variable warnings
+                abort();
+            }
+
              for (gp = guest_argp; gp; gp += sizeof(abi_ulong)) {
                  if (get_user_ual(addr, gp))
                      return -TARGET_EFAULT;
@@ -8769,7 +8799,6 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int 
num, abi_long arg1,
                  argc++;
              }
              envc = 0;
-            guest_envp = arg3;
              for (gp = guest_envp; gp; gp += sizeof(abi_ulong)) {
                  if (get_user_ual(addr, gp))
                      return -TARGET_EFAULT;
@@ -8803,7 +8832,7 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int 
num, abi_long arg1,
              }
              *q = NULL;
  
-            if (!(p = lock_user_string(arg1)))
+            if (!(p = lock_user_string(path)))
                  goto execve_efault;
              /* Although execve() is not an interruptible syscall it is
               * a special case where we must use the safe_syscall wrapper:
@@ -8815,8 +8844,17 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int 
num, abi_long arg1,
               * before the execve completes and makes it the other
               * program's problem.
               */
-            ret = get_errno(safe_execve(p, argp, envp));
-            unlock_user(p, arg1, 0);
+            switch (num) {
+            case TARGET_NR_execve:
+                ret = get_errno(safe_execve(p, argp, envp));
+                break;
+#if defined(TARGET_NR_execveat)
+            case TARGET_NR_execveat:
+                ret = get_errno(safe_execveat(dirfd, p, argp, envp, flags));
+                break;
+#endif
+            }
+            unlock_user(p, path, 0);
  
              goto execve_end;
  


I think it would be clearer to write a common function and to call it from execve and execveat, like 
it's in the kernel:

execve:

  do_execveat(AT_FDCWD, filename, argv, envp, 0);

execeveat:

  do_execveat(fd, filename, argv, envp, flags);

Thanks,
Laurent