semihosting: Split out semihost_sys_open

Split out the non-ARM specific portions of SYS_OPEN to a
reusable function.  This handles gdb and host file i/o.

Add helpers to validate the length of the filename string.
Prepare for usage by other semihosting by allowing the
filename length parameter to be 0, and calling strlen.

Reviewed-by: Luc Michel <lmichel@kalray.eu>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 156 insertions, 0 deletions

diff --git a/semihosting/syscalls.c b/semihosting/syscalls.c
new file mode 100644
index 0000000000..9f9d19a59a
--- /dev/null
+++ b/semihosting/syscalls.c
@@ -0,0 +1,156 @@
+/*
+ * Syscall implementations for semihosting.
+ *
+ * Copyright (c) 2022 Linaro
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "exec/gdbstub.h"
+#include "semihosting/guestfd.h"
+#include "semihosting/syscalls.h"
+#ifdef CONFIG_USER_ONLY
+#include "qemu.h"
+#else
+#include "semihosting/softmmu-uaccess.h"
+#endif
+
+
+/*
+ * Validate or compute the length of the string (including terminator).
+ */
+static int validate_strlen(CPUState *cs, target_ulong str, target_ulong tlen)
+{
+    CPUArchState *env G_GNUC_UNUSED = cs->env_ptr;
+    char c;
+
+    if (tlen == 0) {
+        ssize_t slen = target_strlen(str);
+
+        if (slen < 0) {
+            return -EFAULT;
+        }
+        if (slen >= INT32_MAX) {
+            return -ENAMETOOLONG;
+        }
+        return slen + 1;
+    }
+    if (tlen > INT32_MAX) {
+        return -ENAMETOOLONG;
+    }
+    if (get_user_u8(c, str + tlen - 1)) {
+        return -EFAULT;
+    }
+    if (c != 0) {
+        return -EINVAL;
+    }
+    return tlen;
+}
+
+static int validate_lock_user_string(char **pstr, CPUState *cs,
+                                     target_ulong tstr, target_ulong tlen)
+{
+    int ret = validate_strlen(cs, tstr, tlen);
+    CPUArchState *env G_GNUC_UNUSED = cs->env_ptr;
+    char *str = NULL;
+
+    if (ret > 0) {
+        str = lock_user(VERIFY_READ, tstr, ret, true);
+        ret = str ? 0 : -EFAULT;
+    }
+    *pstr = str;
+    return ret;
+}
+
+/*
+ * GDB semihosting syscall implementations.
+ */
+
+static gdb_syscall_complete_cb gdb_open_complete;
+
+static void gdb_open_cb(CPUState *cs, target_ulong ret, target_ulong err)
+{
+    if (!err) {
+        int guestfd = alloc_guestfd();
+        associate_guestfd(guestfd, ret);
+        ret = guestfd;
+    }
+    gdb_open_complete(cs, ret, err);
+}
+
+static void gdb_open(CPUState *cs, gdb_syscall_complete_cb complete,
+                     target_ulong fname, target_ulong fname_len,
+                     int gdb_flags, int mode)
+{
+    int len = validate_strlen(cs, fname, fname_len);
+    if (len < 0) {
+        complete(cs, -1, -len);
+        return;
+    }
+
+    gdb_open_complete = complete;
+    gdb_do_syscall(gdb_open_cb, "open,%s,%x,%x",
+                   fname, len, (target_ulong)gdb_flags, (target_ulong)mode);
+}
+
+/*
+ * Host semihosting syscall implementations.
+ */
+
+static void host_open(CPUState *cs, gdb_syscall_complete_cb complete,
+                      target_ulong fname, target_ulong fname_len,
+                      int gdb_flags, int mode)
+{
+    CPUArchState *env G_GNUC_UNUSED = cs->env_ptr;
+    char *p;
+    int ret, host_flags;
+
+    ret = validate_lock_user_string(&p, cs, fname, fname_len);
+    if (ret < 0) {
+        complete(cs, -1, -ret);
+        return;
+    }
+
+    if (gdb_flags & GDB_O_WRONLY) {
+        host_flags = O_WRONLY;
+    } else if (gdb_flags & GDB_O_RDWR) {
+        host_flags = O_RDWR;
+    } else {
+        host_flags = O_RDONLY;
+    }
+    if (gdb_flags & GDB_O_CREAT) {
+        host_flags |= O_CREAT;
+    }
+    if (gdb_flags & GDB_O_TRUNC) {
+        host_flags |= O_TRUNC;
+    }
+    if (gdb_flags & GDB_O_EXCL) {
+        host_flags |= O_EXCL;
+    }
+
+    ret = open(p, host_flags, mode);
+    if (ret < 0) {
+        complete(cs, -1, errno);
+    } else {
+        int guestfd = alloc_guestfd();
+        associate_guestfd(guestfd, ret);
+        complete(cs, guestfd, 0);
+    }
+    unlock_user(p, fname, 0);
+}
+
+/*
+ * Syscall entry points.
+ */
+
+void semihost_sys_open(CPUState *cs, gdb_syscall_complete_cb complete,
+                       target_ulong fname, target_ulong fname_len,
+                       int gdb_flags, int mode)
+{
+    if (use_gdb_syscalls()) {
+        gdb_open(cs, complete, fname, fname_len, gdb_flags, mode);
+    } else {
+        host_open(cs, complete, fname, fname_len, gdb_flags, mode);
+    }
+}