Kernel: Add /sys/kernel/request_panic node to simulate a kernel panic

When writing to /sys/kernel/request_panic it will do a kernel panic.
Trying to truncate the node will result in kernel panic with a slightly
different message.

Base/usr/share/man/man7/sys.md

@@ -58,6 +58,7 @@ in system reboot. A written value of `2` results in system shutdown.
 * **`load_base`** - This node reveals the loading address of the kernel.
 * **`system_mode`** - This node exports the chosen system mode as it was decided based on the kernel commandline or a default value.
 * **`cmdline`** - This node exports the kernel boot commandline that was passed from the bootloader.
+* **`request_panic`** - This node allows userspace to trigger (an artificial) kernel panic by writing/truncating it.
 
 #### `net` directory
 

Kernel/CMakeLists.txt

@@ -203,6 +203,7 @@ set(KERNEL_SOURCES
     FileSystem/SysFS/Subsystems/Kernel/Directory.cpp
     FileSystem/SysFS/Subsystems/Kernel/DiskUsage.cpp
     FileSystem/SysFS/Subsystems/Kernel/Log.cpp
+    FileSystem/SysFS/Subsystems/Kernel/RequestPanic.cpp
     FileSystem/SysFS/Subsystems/Kernel/SystemStatistics.cpp
     FileSystem/SysFS/Subsystems/Kernel/GlobalInformation.cpp
     FileSystem/SysFS/Subsystems/Kernel/MemoryStatus.cpp

Kernel/FileSystem/SysFS/Subsystems/Kernel/Directory.cpp

@@ -23,6 +23,7 @@
 #include <Kernel/FileSystem/SysFS/Subsystems/Kernel/PowerStateSwitch.h>
 #include <Kernel/FileSystem/SysFS/Subsystems/Kernel/Processes.h>
 #include <Kernel/FileSystem/SysFS/Subsystems/Kernel/Profile.h>
+#include <Kernel/FileSystem/SysFS/Subsystems/Kernel/RequestPanic.h>
 #include <Kernel/FileSystem/SysFS/Subsystems/Kernel/SystemStatistics.h>
 #include <Kernel/FileSystem/SysFS/Subsystems/Kernel/Uptime.h>
 
@@ -44,6 +45,7 @@ UNMAP_AFTER_INIT NonnullRefPtr<SysFSGlobalKernelStatsDirectory> SysFSGlobalKerne
         list.append(SysFSProfile::must_create(*global_kernel_stats_directory));
         list.append(SysFSPowerStateSwitchNode::must_create(*global_kernel_stats_directory));
         list.append(SysFSJails::must_create(*global_kernel_stats_directory));
+        list.append(SysFSSystemRequestPanic::must_create(*global_kernel_stats_directory));
 
         list.append(SysFSGlobalNetworkStatsDirectory::must_create(*global_kernel_stats_directory));
         list.append(SysFSKernelConfigurationDirectory::must_create(*global_kernel_stats_directory));

Kernel/FileSystem/SysFS/Subsystems/Kernel/RequestPanic.cpp

@@ -0,0 +1,48 @@
+/*
+ * Copyright (c) 2023, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <Kernel/FileSystem/SysFS/Subsystems/Kernel/RequestPanic.h>
+#include <Kernel/Library/Panic.h>
+#include <Kernel/Security/Jail.h>
+#include <Kernel/Tasks/Process.h>
+
+namespace Kernel {
+
+UNMAP_AFTER_INIT NonnullRefPtr<SysFSSystemRequestPanic> SysFSSystemRequestPanic::must_create(SysFSDirectory const& parent_directory)
+{
+    return adopt_ref_if_nonnull(new (nothrow) SysFSSystemRequestPanic(parent_directory)).release_nonnull();
+}
+
+static ErrorOr<void> check_current_process_not_jailed()
+{
+    return Process::current().jail().with([&](auto const& my_jail) -> ErrorOr<void> {
+        if (my_jail)
+            return Error::from_errno(EPERM);
+        return {};
+    });
+}
+
+ErrorOr<size_t> SysFSSystemRequestPanic::read_bytes(off_t, size_t, UserOrKernelBuffer&, OpenFileDescription*) const
+{
+    TRY(check_current_process_not_jailed());
+    return Error::from_errno(ENOTSUP);
+}
+
+ErrorOr<size_t> SysFSSystemRequestPanic::write_bytes(off_t, size_t, UserOrKernelBuffer const&, OpenFileDescription*)
+{
+    TRY(check_current_process_not_jailed());
+    PANIC("SysFSSystemRequestPanic::write_bytes");
+    VERIFY_NOT_REACHED();
+}
+
+ErrorOr<void> SysFSSystemRequestPanic::truncate(u64)
+{
+    TRY(check_current_process_not_jailed());
+    PANIC("SysFSSystemRequestPanic::truncate");
+    VERIFY_NOT_REACHED();
+}
+
+}

Kernel/FileSystem/SysFS/Subsystems/Kernel/RequestPanic.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2023, Liav A. <liavalb@hotmail.co.il>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Error.h>
+#include <AK/Function.h>
+#include <AK/RefPtr.h>
+#include <AK/Types.h>
+#include <Kernel/FileSystem/OpenFileDescription.h>
+#include <Kernel/FileSystem/SysFS/Component.h>
+#include <Kernel/Library/KBufferBuilder.h>
+#include <Kernel/Library/UserOrKernelBuffer.h>
+
+namespace Kernel {
+
+class SysFSSystemRequestPanic final : public SysFSComponent {
+public:
+    static NonnullRefPtr<SysFSSystemRequestPanic> must_create(SysFSDirectory const& parent_directory);
+    virtual StringView name() const override { return "request_panic"sv; }
+
+private:
+    explicit SysFSSystemRequestPanic(SysFSDirectory const& parent_directory)
+        : SysFSComponent(parent_directory)
+    {
+    }
+
+    // ^SysFSComponent
+    virtual ErrorOr<size_t> read_bytes(off_t offset, size_t count, UserOrKernelBuffer& buffer, OpenFileDescription* description) const override;
+    virtual ErrorOr<size_t> write_bytes(off_t, size_t, UserOrKernelBuffer const&, OpenFileDescription*) override;
+    virtual mode_t permissions() const override { return 0600; }
+    virtual ErrorOr<void> truncate(u64) override;
+};
+
+}

Meta/gn/secondary/Kernel/BUILD.gn

@@ -657,6 +657,7 @@ executable("Kernel_bin") {
     "FileSystem/SysFS/Subsystems/Kernel/PowerStateSwitch.cpp",
     "FileSystem/SysFS/Subsystems/Kernel/Processes.cpp",
     "FileSystem/SysFS/Subsystems/Kernel/Profile.cpp",
+    "FileSystem/SysFS/Subsystems/Kernel/RequestPanic.cpp",
     "FileSystem/SysFS/Subsystems/Kernel/SystemStatistics.cpp",
     "FileSystem/SysFS/Subsystems/Kernel/Uptime.cpp",
     "FileSystem/SysFS/Subsystems/Kernel/Variables/BooleanVariable.cpp",