Utilities: Enable syscall(1) to use SC_*_params buffers

Author: https://github.com/BenWiederhake
Commit: https://github.com/SerenityOS/serenity/commit/cb9a9a3e03a
Pull-request: https://github.com/SerenityOS/serenity/pull/5294

Userland/Utilities/syscall.cpp

@@ -24,7 +24,10 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <AK/Iterator.h>
+#include <AK/Vector.h>
 #include <LibCore/ArgsParser.h>
+#include <mman.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -33,9 +36,12 @@
 #define SC_NARG 4
 
 FlatPtr arg[SC_NARG];
-char buf[BUFSIZ];
+char outbuf[BUFSIZ];
 
-static FlatPtr parse(const char* s);
+using Arguments = Vector<const char*>;
+using ArgIter = Arguments::Iterator;
+
+static FlatPtr parse_from(ArgIter&);
 
 int main(int argc, char** argv)
 {
@@ -46,45 +52,102 @@ int main(int argc, char** argv)
     Core::ArgsParser args_parser;
     args_parser.add_option(output_buffer, "Output the contents of the buffer (beware of stray zero bytes!)", "output-buffer", 'o');
     args_parser.add_option(list_syscalls, "List all existing syscalls", "list-syscalls", 'l');
-    args_parser.add_positional_argument(arguments, "Syscall arguments (can be strings, 'buf' for the output buffer, or numbers like 1234 or 0xffffffff)", "syscall-arguments");
+    args_parser.add_positional_argument(arguments, "Syscall arguments; can be a string, 'buf' for the output buffer, or numbers like 1234 or 0xffffffff, or a buffer that must begin with '[' and end with ']'. If the first character is ',' (comma), the argument is interpreted as a string, no matter what. This is useful if the string is '[' or '0x0'.", "syscall-arguments");
     args_parser.parse(argc, argv);
 
-    for (size_t i = 0; i < arguments.size(); i++) {
-        arg[i] = parse(arguments[i]);
+    ArgIter iter = arguments.begin();
+    for (size_t i = 0; i < SC_NARG && !iter.is_end(); i++) {
+        arg[i] = parse_from(iter);
+    }
+    if (!iter.is_end()) {
+        fprintf(stderr, "Too many arguments (did you want to use '[ parameter buffers ]'?)\n");
+        return -1;
     }
 
-    for (int sc = 0; sc < Syscall::Function::__Count; ++sc) {
-        if (strcmp(Syscall::to_string((Syscall::Function)sc), (char*)arg[0]) == 0) {
-            int rc = syscall(sc, arg[1], arg[2], arg[3]);
-            if (rc == -1) {
-                perror("syscall");
-            } else {
-                if (output_buffer)
-                    fwrite(buf, 1, sizeof(buf), stdout);
+    if (arg[0] > Syscall::Function::__Count) {
+        for (int sc = 0; sc < Syscall::Function::__Count; ++sc) {
+            if (strcmp(Syscall::to_string((Syscall::Function)sc), (char*)arg[0]) == 0) {
+                arg[0] = sc;
+                break;
             }
-
-            fprintf(stderr, "Syscall return: %d\n", rc);
-            return 0;
+        }
+        if (arg[0] > Syscall::Function::__Count) {
+            fprintf(stderr, "Invalid syscall entry %s\n", (char*)arg[0]);
+            return -1;
         }
     }
 
-    fprintf(stderr, "Invalid syscall entry %s\n", (char*)arg[0]);
-    return -1;
+    int rc = syscall(arg[0], arg[1], arg[2], arg[3]);
+    if (rc == -1)
+        perror("syscall");
+    if (output_buffer)
+        fwrite(outbuf, 1, sizeof(outbuf), stdout);
+
+    fprintf(stderr, "Syscall return: %d\n", rc);
+    return 0;
 }
 
-FlatPtr parse(const char* s)
+static FlatPtr as_buf(Vector<FlatPtr> params_vec)
 {
-    char* t;
-    FlatPtr l;
+    size_t params_size = sizeof(FlatPtr) * params_vec.size();
+    size_t buf_size = round_up_to_power_of_two(params_size + 1, PAGE_SIZE);
+    void* buf = mmap(nullptr, buf_size, PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, 0, 0);
+    if (buf == MAP_FAILED) {
+        fprintf(stderr, "Warning: Could not allocate buffer of size %zu (low memory?)\n", buf_size);
+        exit(1);
+    }
+    // It's probably good to ensure zero-initialization.
+    memset(buf, 0, buf_size);
+    memcpy(buf, params_vec.data(), params_size);
+    // Leak the buffer here. We need to keep it until the special syscall happens,
+    // and we terminate immediately afterwards anyway.
+    return (FlatPtr)buf;
+}
 
-    if (strcmp(s, "buf") == 0) {
-        return (FlatPtr)buf;
+static FlatPtr parse_parameter_buffer(ArgIter& iter)
+{
+    Vector<FlatPtr> params_vec;
+    while (!iter.is_end()) {
+        if (strcmp(*iter, "]") == 0) {
+            ++iter;
+            return as_buf(params_vec);
+        }
+
+        params_vec.append(parse_from(iter));
     }
 
-    l = strtoul(s, &t, 0);
-    if (t > s && *t == 0) {
+    fprintf(stderr, "Warning: Treating unmatched ']' as literal string\n");
+    exit(1);
+    ASSERT_NOT_REACHED();
+}
+
+static FlatPtr parse_from(ArgIter& iter)
+{
+    const char* this_arg = *iter;
+    ++iter;
+
+    // Is it a forced literal?
+    if (this_arg[0] == ',')
+        return (FlatPtr)(this_arg + 1);
+
+    // Is it the output buffer?
+    if (strcmp(this_arg, "buf") == 0)
+        return (FlatPtr)outbuf;
+
+    // Is it a parameter buffer?
+    if (strcmp(this_arg, "[") == 0)
+        return parse_parameter_buffer(iter);
+
+    // Is it a number?
+    char* endptr = nullptr;
+    FlatPtr l = strtoul(this_arg, &endptr, 0);
+    if (*endptr == 0) {
         return l;
     }
 
-    return (FlatPtr)s;
+    // Then it must be a string:
+    if (strcmp(this_arg, "]") == 0)
+        fprintf(stderr, "Warning: Treating unmatched ']' as literal string\n");
+
+    return (FlatPtr)this_arg;
 }