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Re: [PATCH v3] linux-user: implement execveat


From: Helge Deller
Subject: Re: [PATCH v3] linux-user: implement execveat
Date: Thu, 3 Nov 2022 20:54:00 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.0

On 11/3/22 18:32, Drew DeVault wrote:
References: https://gitlab.com/qemu-project/qemu/-/issues/1007
Signed-off-by: Drew DeVault <sir@cmpwn.com>
---
v2 => v3:
- Rebase to address the is_proc_myself fix
- Drop the ifdefs

  linux-user/syscall.c | 203 ++++++++++++++++++++++---------------------
  1 file changed, 105 insertions(+), 98 deletions(-)


I'd suggest you add the missing strace part as well.
See in strace.list and compare what's done for execve.

Helge




diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 8402c1399d..38fbbbad6a 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -689,7 +689,8 @@ safe_syscall4(pid_t, wait4, pid_t, pid, int *, status, int, 
options, \
  #endif
  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)
+safe_syscall5(int, execveat, int, dirfd, const char *, filename,
+        char **, argv, char **, envp, int, flags)
  #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, \
@@ -8349,6 +8350,106 @@ static int do_openat(CPUArchState *cpu_env, int dirfd, 
const char *pathname, int
      return safe_openat(dirfd, path(pathname), flags, mode);
  }

+static int do_execveat(CPUArchState *cpu_env, int dirfd, abi_long pathname, 
abi_long guest_argp, abi_long guest_envp, int flags)
+{
+    int ret;
+    char **argp, **envp;
+    int argc, envc;
+    abi_ulong gp;
+    abi_ulong addr;
+    char **q;
+    void *p;
+
+    argc = 0;
+
+    for (gp = guest_argp; gp; gp += sizeof(abi_ulong)) {
+        if (get_user_ual(addr, gp))
+            return -TARGET_EFAULT;
+        if (!addr)
+            break;
+        argc++;
+    }
+    envc = 0;
+    for (gp = guest_envp; gp; gp += sizeof(abi_ulong)) {
+        if (get_user_ual(addr, gp))
+            return -TARGET_EFAULT;
+        if (!addr)
+            break;
+        envc++;
+    }
+
+    argp = g_new0(char *, argc + 1);
+    envp = g_new0(char *, envc + 1);
+
+    for (gp = guest_argp, q = argp; gp;
+          gp += sizeof(abi_ulong), q++) {
+        if (get_user_ual(addr, gp))
+            goto execve_efault;
+        if (!addr)
+            break;
+        if (!(*q = lock_user_string(addr)))
+            goto execve_efault;
+    }
+    *q = NULL;
+
+    for (gp = guest_envp, q = envp; gp;
+          gp += sizeof(abi_ulong), q++) {
+        if (get_user_ual(addr, gp))
+            goto execve_efault;
+        if (!addr)
+            break;
+        if (!(*q = lock_user_string(addr)))
+            goto execve_efault;
+    }
+    *q = NULL;
+
+    /* Although execve() is not an interruptible syscall it is
+     * a special case where we must use the safe_syscall wrapper:
+     * if we allow a signal to happen before we make the host
+     * syscall then we will 'lose' it, because at the point of
+     * execve the process leaves QEMU's control. So we use the
+     * safe syscall wrapper to ensure that we either take the
+     * signal as a guest signal, or else it does not happen
+     * before the execve completes and makes it the other
+     * program's problem.
+     */
+    if (!(p = lock_user_string(pathname)))
+        goto execve_efault;
+
+    if (is_proc_myself(p, "exe")) {
+        ret = get_errno(safe_execveat(dirfd, exec_path, argp, envp, flags));
+    } else {
+        ret = get_errno(safe_execveat(dirfd, p, argp, envp, flags));
+    }
+
+    unlock_user(p, pathname, 0);
+
+    goto execve_end;
+
+execve_efault:
+    ret = -TARGET_EFAULT;
+
+execve_end:
+    for (gp = guest_argp, q = argp; *q;
+          gp += sizeof(abi_ulong), q++) {
+        if (get_user_ual(addr, gp)
+            || !addr)
+            break;
+        unlock_user(*q, addr, 0);
+    }
+    for (gp = guest_envp, q = envp; *q;
+          gp += sizeof(abi_ulong), q++) {
+        if (get_user_ual(addr, gp)
+            || !addr)
+            break;
+        unlock_user(*q, addr, 0);
+    }
+
+    g_free(argp);
+    g_free(envp);
+    return ret;
+}
+
  #define TIMER_MAGIC 0x0caf0000
  #define TIMER_MAGIC_MASK 0xffff0000

@@ -8846,104 +8947,10 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int 
num, abi_long arg1,
          unlock_user(p, arg2, 0);
          return ret;
  #endif
+    case TARGET_NR_execveat:
+        return do_execveat(cpu_env, arg1, arg2, arg3, arg4, arg5);
      case TARGET_NR_execve:
-        {
-            char **argp, **envp;
-            int argc, envc;
-            abi_ulong gp;
-            abi_ulong guest_argp;
-            abi_ulong guest_envp;
-            abi_ulong addr;
-            char **q;
-
-            argc = 0;
-            guest_argp = arg2;
-            for (gp = guest_argp; gp; gp += sizeof(abi_ulong)) {
-                if (get_user_ual(addr, gp))
-                    return -TARGET_EFAULT;
-                if (!addr)
-                    break;
-                argc++;
-            }
-            envc = 0;
-            guest_envp = arg3;
-            for (gp = guest_envp; gp; gp += sizeof(abi_ulong)) {
-                if (get_user_ual(addr, gp))
-                    return -TARGET_EFAULT;
-                if (!addr)
-                    break;
-                envc++;
-            }
-
-            argp = g_new0(char *, argc + 1);
-            envp = g_new0(char *, envc + 1);
-
-            for (gp = guest_argp, q = argp; gp;
-                  gp += sizeof(abi_ulong), q++) {
-                if (get_user_ual(addr, gp))
-                    goto execve_efault;
-                if (!addr)
-                    break;
-                if (!(*q = lock_user_string(addr)))
-                    goto execve_efault;
-            }
-            *q = NULL;
-
-            for (gp = guest_envp, q = envp; gp;
-                  gp += sizeof(abi_ulong), q++) {
-                if (get_user_ual(addr, gp))
-                    goto execve_efault;
-                if (!addr)
-                    break;
-                if (!(*q = lock_user_string(addr)))
-                    goto execve_efault;
-            }
-            *q = NULL;
-
-            if (!(p = lock_user_string(arg1)))
-                goto execve_efault;
-            /* Although execve() is not an interruptible syscall it is
-             * a special case where we must use the safe_syscall wrapper:
-             * if we allow a signal to happen before we make the host
-             * syscall then we will 'lose' it, because at the point of
-             * execve the process leaves QEMU's control. So we use the
-             * safe syscall wrapper to ensure that we either take the
-             * signal as a guest signal, or else it does not happen
-             * before the execve completes and makes it the other
-             * program's problem.
-             */
-            if (is_proc_myself(p, "exe")) {
-                ret = get_errno(safe_execve(exec_path, argp, envp));
-            } else {
-                ret = get_errno(safe_execve(p, argp, envp));
-            }
-            unlock_user(p, arg1, 0);
-
-            goto execve_end;
-
-        execve_efault:
-            ret = -TARGET_EFAULT;
-
-        execve_end:
-            for (gp = guest_argp, q = argp; *q;
-                  gp += sizeof(abi_ulong), q++) {
-                if (get_user_ual(addr, gp)
-                    || !addr)
-                    break;
-                unlock_user(*q, addr, 0);
-            }
-            for (gp = guest_envp, q = envp; *q;
-                  gp += sizeof(abi_ulong), q++) {
-                if (get_user_ual(addr, gp)
-                    || !addr)
-                    break;
-                unlock_user(*q, addr, 0);
-            }
-
-            g_free(argp);
-            g_free(envp);
-        }
-        return ret;
+        return do_execveat(cpu_env, AT_FDCWD, arg1, arg2, arg3, 0);
      case TARGET_NR_chdir:
          if (!(p = lock_user_string(arg1)))
              return -TARGET_EFAULT;




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