[Zion] Add a way to unwind the stack and recover from user-space faults.

zion/CMakeLists.txt

@@ -6,6 +6,7 @@ add_executable(zion
   common/gdt.cpp
   common/load_gdt.s
   common/msr.cpp
+  common/stack_unwind.cpp
   debug/debug.cpp
   interrupt/apic.cpp
   interrupt/apic_timer.cpp

zion/common/stack_unwind.cpp

@@ -0,0 +1,20 @@
+#include "common/stack_unwind.h"
+
+#include "debug/debug.h"
+
+namespace {
+
+bool IsValid(uint64_t* rbp) { return rbp && *rbp != kStackBaseSentinel; }
+
+}  // namespace
+
+void StackUnwind(uint64_t rbp) {
+  dbgln("-- Begin Stack --");
+  uint64_t* rbp_ptr = reinterpret_cast<uint64_t*>(rbp);
+  while (IsValid(rbp_ptr)) {
+    uint64_t rip = *(rbp_ptr + 1);
+    dbgln("RIP: {x}", rip);
+    rbp_ptr = reinterpret_cast<uint64_t*>(*rbp_ptr);
+  }
+  dbgln("-- End Stack --");
+}

zion/common/stack_unwind.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#include <stdint.h>
+
+const uint64_t kStackBaseSentinel = 0xABBACDCD'12345678;
+
+void StackUnwind(uint64_t rbp);

zion/interrupt/interrupt.cpp

@@ -3,6 +3,7 @@
 #include <stdint.h>
 
 #include "common/port.h"
+#include "common/stack_unwind.h"
 #include "debug/debug.h"
 #include "interrupt/apic.h"
 #include "interrupt/apic_timer.h"
@@ -69,15 +70,29 @@ struct InterruptFrame {
   uint64_t ss;
 };
 
+bool IsUserSpace(uint64_t addr) { return (addr & (1l << 63)) == 0; }
+
 extern "C" void isr_divide_by_zero();
 extern "C" void interrupt_divide_by_zero(InterruptFrame* frame) {
   dbgln("RIP: {x}", frame->rip);
+  StackUnwind(frame->rbp);
+
+  if (IsUserSpace(frame->rip)) {
+    gScheduler->CurrentProcess().Exit();
+    UNREACHABLE
+  }
   panic("DIV0");
 }
 
 extern "C" void isr_invalid_opcode();
 extern "C" void interrupt_invalid_opcode(InterruptFrame* frame) {
   dbgln("RIP: {x}", frame->rip);
+  StackUnwind(frame->rbp);
+
+  if (IsUserSpace(frame->rip)) {
+    gScheduler->CurrentProcess().Exit();
+    UNREACHABLE
+  }
   panic("INVALID OPCODE");
 }
 
@@ -96,7 +111,12 @@ extern "C" void interrupt_protection_fault(InterruptFrame* frame) {
   dbgln("Index: {}", err >> 3);
   dbgln("RIP: {x}", frame->rip);
   dbgln("RSP: {x}", frame->rsp);
+  StackUnwind(frame->rbp);
 
+  if (IsUserSpace(frame->rip)) {
+    gScheduler->CurrentProcess().Exit();
+    UNREACHABLE
+  }
   panic("GP");
 }
 
@@ -133,11 +153,23 @@ extern "C" void interrupt_page_fault(InterruptFrame* frame) {
 
   dbgln("rip:  {x}", frame->rip);
   dbgln("addr: {x}", frame->cr2);
+  StackUnwind(frame->rbp);
+
+  if (IsUserSpace(frame->rip)) {
+    gScheduler->CurrentProcess().Exit();
+    UNREACHABLE
+  }
+
   panic("PF");
 }
 
 extern "C" void isr_fpe_fault();
 extern "C" void interrupt_fpe_fault(InterruptFrame* frame) {
+  dbgln("Floating point exception.");
+  if (IsUserSpace(frame->rip)) {
+    gScheduler->CurrentProcess().Exit();
+    UNREACHABLE
+  }
   panic("Floating point exception");
 }
 

zion/object/thread.cpp

@@ -1,6 +1,7 @@
 #include "object/thread.h"
 
 #include "common/gdt.h"
+#include "common/stack_unwind.h"
 #include "debug/debug.h"
 #include "memory/kernel_vmm.h"
 #include "memory/paging_util.h"
@@ -71,6 +72,7 @@ void Thread::Init() {
   // will emit movaps calls to non-16-bit-aligned stack
   // addresses.
   rsp -= 0x8;
+  *reinterpret_cast<uint64_t*>(rsp) = kStackBaseSentinel;
   SetRsp0(rsp0_start_);
   jump_user_space(rip_, rsp, arg1_, arg2_);
 }

zion/scheduler/jump_user_space.s

@@ -8,6 +8,7 @@ jump_user_space:
   mov %ax, %fs
   mov %ax, %gs
 
+  mov %rsi, %rbp
   pushq $0x23 # ss
   pushq %rsi
   pushq $0x202  # Bit 9 enables interrupts.