From 5d94525c7a1bd68a9928d531821b24a515529df9 Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Sun, 6 Nov 2022 18:12:25 +0100
Subject: [PATCH] Kernel: Figure out why a program is misbehaving

---
 kernel/include/utils/PageFaultReason.h |  4 ++++
 kernel/src/interrupts/Entry.cpp        |  8 ++++++++
 kernel/src/utils/PageFaultReason.cpp   | 20 ++++++++++++++++++++
 3 files changed, 32 insertions(+)
 create mode 100644 kernel/include/utils/PageFaultReason.h
 create mode 100644 kernel/src/utils/PageFaultReason.cpp

diff --git a/kernel/include/utils/PageFaultReason.h b/kernel/include/utils/PageFaultReason.h
new file mode 100644
index 00000000..7f9d88da
--- /dev/null
+++ b/kernel/include/utils/PageFaultReason.h
@@ -0,0 +1,4 @@
+#pragma once
+#include <stdint.h>
+
+void determine_user_page_fault_reason(uintptr_t faulting_address);
\ No newline at end of file
diff --git a/kernel/src/interrupts/Entry.cpp b/kernel/src/interrupts/Entry.cpp
index 1431a292..37f86b22 100644
--- a/kernel/src/interrupts/Entry.cpp
+++ b/kernel/src/interrupts/Entry.cpp
@@ -5,6 +5,7 @@
 #include "interrupts/Interrupts.h"
 #include "io/Serial.h"
 #include "log/Log.h"
+#include "memory/VMM.h"
 #include "misc/hang.h"
 #include "panic/Panic.h"
 #include "std/assert.h"
@@ -12,6 +13,7 @@
 #include "sys/Syscall.h"
 #include "thread/Scheduler.h"
 #include "trace/StackTracer.h"
+#include "utils/PageFaultReason.h"
 
 extern "C" void common_handler(Context* context)
 {
@@ -28,6 +30,8 @@ extern "C" void common_handler(Context* context)
         if (context->cs == 0x8) { int_panic(context, "GPF in kernel task"); }
         else
         {
+            VMM::enter_syscall_context();
+
             kerrorln("General protection fault at RIP %lx, cs %ld, ss %ld, RSP %lx, error code %ld", context->rip,
                      context->cs, context->ss, context->rsp, context->error_code);
             kinfoln("Stack trace:");
@@ -44,6 +48,8 @@ extern "C" void common_handler(Context* context)
         if (context->cs == 0x8) { int_panic(context, "Page fault in kernel task"); }
         else
         {
+            VMM::enter_syscall_context();
+
             kerrorln("Page fault in ring 3 (RIP %lx), while trying to access %lx, error code %ld", context->rip,
                      context->cr2, context->error_code);
             kinfoln("Stack trace:");
@@ -51,6 +57,8 @@ extern "C" void common_handler(Context* context)
             StackTracer tracer(context->rbp);
             tracer.trace_with_ip(context->rip);
 
+            determine_user_page_fault_reason(context->cr2);
+
             Scheduler::task_misbehave(context, -3);
         }
     }
diff --git a/kernel/src/utils/PageFaultReason.cpp b/kernel/src/utils/PageFaultReason.cpp
new file mode 100644
index 00000000..054a2294
--- /dev/null
+++ b/kernel/src/utils/PageFaultReason.cpp
@@ -0,0 +1,20 @@
+#define MODULE "mem"
+
+#include "utils/PageFaultReason.h"
+#include "log/Log.h"
+
+#define PROGRAM_STACK_BOTTOM 0x100000
+
+void determine_user_page_fault_reason(uintptr_t faulting_address)
+{
+    if (faulting_address < 0x1000)
+    {
+        kinfoln("Address 0x%lx looks like a nullptr dereference", faulting_address);
+        return;
+    }
+    if (faulting_address < PROGRAM_STACK_BOTTOM && (PROGRAM_STACK_BOTTOM - faulting_address) < 0x1000)
+    {
+        kinfoln("Address 0x%lx looks like a stack overflow", faulting_address);
+        return;
+    }
+}
\ No newline at end of file