From dd62f2e3e1b69310ebc28672820fff0817fc7267 Mon Sep 17 00:00:00 2001
From: Pawel Wieczorkiewicz <wipawel@grsecurity.net>
Date: Fri, 8 Jul 2022 14:31:50 +0200
Subject: [PATCH] usermode: handle usermode exceptions

Exceptions occuring in usermode terminate a user task, but are not fatal
for the kernel.

Signed-off-by: Pawel Wieczorkiewicz <wipawel@grsecurity.net>
---
 arch/x86/traps.c   | 11 +++++++++--
 include/usermode.h |  5 +++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/traps.c b/arch/x86/traps.c
index fa7da76b..915b2b4e 100644
--- a/arch/x86/traps.c
+++ b/arch/x86/traps.c
@@ -27,6 +27,7 @@
 #include <drivers/keyboard.h>
 #include <drivers/pit.h>
 #include <drivers/serial.h>
+#include <errno.h>
 #include <extables.h>
 #include <ktf.h>
 #include <mm/regions.h>
@@ -34,9 +35,9 @@
 #include <segment.h>
 #include <symbols.h>
 #include <traps.h>
+#include <usermode.h>
 
 #include <mm/vmm.h>
-#include <usermode.h>
 
 extern void asm_interrupt_handler_uart(void);
 extern void asm_interrupt_handler_keyboard(void);
@@ -298,7 +299,7 @@ static bool extables_fixup(struct cpu_regs *regs) {
 void do_exception(struct cpu_regs *regs) {
     static char ec_str[32], panic_str[128];
 
-    if (extables_fixup(regs))
+    if (!from_usermode(regs->cs) && extables_fixup(regs))
         return;
 
     dump_regs(regs);
@@ -312,5 +313,11 @@ void do_exception(struct cpu_regs *regs) {
              exception_names[regs->vector], ec_str, regs->cs, regs->_ASM_IP, regs->ss,
              regs->_ASM_SP);
 
+    /* Handle user tasks' exceptions */
+    if (from_usermode(regs->cs)) {
+        printk("Task exception: %s\n", panic_str);
+        goto_syscall_exit(-EFAULT);
+    }
+
     panic(panic_str);
 }
diff --git a/include/usermode.h b/include/usermode.h
index 03b7fc01..8a7acfea 100644
--- a/include/usermode.h
+++ b/include/usermode.h
@@ -37,6 +37,11 @@ static inline bool from_usermode(uint16_t cs) {
     return (cs & 0x3) != 0;
 }
 
+static inline void goto_syscall_exit(long exit_code) {
+    swapgs();
+    asm volatile("jmp syscall_handler" ::"A"(SYSCALL_EXIT), "D"(exit_code));
+}
+
 /* External declarations */
 
 extern unsigned long enter_usermode(task_func_t fn, void *fn_arg,