Userland: Introduce the pmemdump utility

This utility helps to dump the physical memory space from /dev/mem.
It supports both read(2) and mmap(2) on it so we could use mmap(2) for
fast dumping of the memory, or read(2) when we need to read unaligned
physical regions.

Base/usr/share/man/man1/pmemdump.md

@@ -0,0 +1,38 @@
+## Name
+
+pmemdump - dump physical memory
+
+## Synopsis
+
+```**sh
+$ pmemdump [-r] <offset> <length>
+```
+
+## Description
+
+Dump a portion of the physical memory space.
+
+
+## Options
+
+* `-r`: Dump from /dev/mem with `read(2)` instead of doing `mmap(2)` on it.
+
+## Examples
+
+```sh
+$ pmemdump -r 983040 65536 
+$ pmemdump 983040 65536 
+```
+
+## Notes
+
+The pmemdump utility opens the `/dev/mem` file, and gets a mapping by doing `mmap(2)`
+on it.
+
+Using the `-r` flag might be useful sometimes, especially when reading from an unaligned
+reserved physical memory region when trying to `mmap(2)` `/dev/mem` on the specified
+offset fails.
+
+## See also
+
+* [`mem`(4)](../man4/mem.md)

Userland/Utilities/CMakeLists.txt

@@ -130,6 +130,7 @@ target_link_libraries(paste LibGUI)
 target_link_libraries(pgrep LibRegex)
 target_link_libraries(pls LibCrypt LibMain)
 target_link_libraries(pmap LibMain)
+target_link_libraries(pmemdump LibMain)
 target_link_libraries(pro LibMain LibProtocol)
 target_link_libraries(ps LibMain)
 target_link_libraries(pwd LibMain)

Userland/Utilities/pmemdump.cpp

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+/*
+ * Copyright (c) 2021, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/String.h>
+#include <AK/StringUtils.h>
+#include <LibCore/ArgsParser.h>
+#include <LibCore/System.h>
+#include <LibMain/Main.h>
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <inttypes.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+static bool try_set_offset_and_length_parameters(String const& arg_offset, String const& arg_length, u64& offset, u64& length)
+{
+    // TODO: Add support for hex values
+    auto possible_offset = arg_offset.to_uint<u64>();
+    if (!possible_offset.has_value())
+        return false;
+    auto possible_length = arg_length.to_uint<u64>();
+    if (!possible_length.has_value())
+        return false;
+    offset = possible_offset.value();
+    length = possible_length.value();
+    return true;
+}
+
+static void try_to_dump_with_memory_mapping(int fd, u64 offset, u64 length)
+{
+    VERIFY(fd >= 0);
+    u64 mmoffset = offset % sysconf(_SC_PAGESIZE);
+    void* mmp = mmap(NULL, mmoffset + length, PROT_READ, MAP_SHARED, fd, offset - mmoffset);
+    if (mmp == MAP_FAILED) {
+        perror("mmap");
+        return;
+    }
+
+    size_t ncomplete = 0;
+    while (ncomplete < length) {
+        ssize_t nwritten = write(STDOUT_FILENO, static_cast<u8*>(mmp) + ncomplete, length - ncomplete);
+        if (nwritten < 0) {
+            perror("write");
+            return;
+        }
+        ncomplete += nwritten;
+    }
+    if (munmap(mmp, mmoffset + length) < 0) {
+        perror("munmap");
+    }
+}
+
+static void try_to_dump_with_read(int fd, u64 offset, u64 length)
+{
+    VERIFY(fd >= 0);
+    auto rs = lseek(fd, offset, SEEK_SET);
+    if (rs < 0) {
+        fprintf(stderr, "Couldn't seek to offset %" PRIi64 " while verifying: %s\n", offset, strerror(errno));
+        return;
+    }
+    u8 buf[4096];
+    size_t ncomplete = 0;
+    while (ncomplete < length) {
+        size_t length_to_be_read = min<size_t>((length - ncomplete), sizeof(buf));
+        if (read(fd, buf, length_to_be_read) < 0) {
+            perror("read");
+            return;
+        }
+        ssize_t nwritten = write(STDOUT_FILENO, buf, length_to_be_read);
+        if (nwritten < 0) {
+            perror("write");
+            return;
+        }
+        ncomplete += nwritten;
+    }
+}
+
+ErrorOr<int> serenity_main(Main::Arguments arguments)
+{
+    TRY(Core::System::pledge("stdio rpath"));
+
+    StringView arg_offset;
+    StringView arg_length;
+    bool use_read_instead_of_mmap = false;
+    Core::ArgsParser args;
+    args.add_positional_argument(arg_offset, "Physical Address (Offset)", "offset", Core::ArgsParser::Required::Yes);
+    args.add_positional_argument(arg_length, "Length of that region", "length", Core::ArgsParser::Required::Yes);
+    args.add_option(use_read_instead_of_mmap, "Read /dev/mem instead of try to map it", nullptr, 'r');
+
+    args.parse(arguments);
+
+    u64 offset = 0;
+    u64 length = 0;
+    if (!try_set_offset_and_length_parameters(arg_offset, arg_length, offset, length)) {
+        warnln("pmemdump: Invalid length or offset parameters\n");
+        return 1;
+    }
+
+    int fd = open("/dev/mem", O_RDONLY);
+    if (fd < 0) {
+        perror("open");
+        return 1;
+    }
+    if (use_read_instead_of_mmap)
+        try_to_dump_with_read(fd, offset, length);
+    else
+        try_to_dump_with_memory_mapping(fd, offset, length);
+
+    close(fd);
+
+    return 0;
+}