1 files changed, 122 insertions, 9 deletions

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 725ef4d17cd..43f1281d440 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -109,6 +109,78 @@ static inline void preempt_conditional_cli(struct pt_regs *regs)
 	dec_preempt_count();
 }
 
+#ifdef CONFIG_X86_32
+static inline int
+__compare_user_cs_desc(const struct desc_struct *desc1,
+	const struct desc_struct *desc2)
+{
+	return ((desc1->limit0 != desc2->limit0) ||
+		(desc1->limit != desc2->limit) ||
+		(desc1->base0 != desc2->base0) ||
+		(desc1->base1 != desc2->base1) ||
+		(desc1->base2 != desc2->base2));
+}
+
+/*
+ * lazy-check for CS validity on exec-shield binaries:
+ *
+ * the original non-exec stack patch was written by
+ * Solar Designer <solar at openwall.com>. Thanks!
+ */
+static int
+check_lazy_exec_limit(int cpu, struct pt_regs *regs, long error_code)
+{
+	struct desc_struct *desc1, *desc2;
+	struct vm_area_struct *vma;
+	unsigned long limit;
+
+	if (current->mm == NULL)
+		return 0;
+
+	limit = -1UL;
+	if (current->mm->context.exec_limit != -1UL) {
+		limit = PAGE_SIZE;
+		spin_lock(&current->mm->page_table_lock);
+		for (vma = current->mm->mmap; vma; vma = vma->vm_next)
+			if ((vma->vm_flags & VM_EXEC) && (vma->vm_end > limit))
+				limit = vma->vm_end;
+		vma = get_gate_vma(current);
+		if (vma && (vma->vm_flags & VM_EXEC) && (vma->vm_end > limit))
+			limit = vma->vm_end;
+		spin_unlock(&current->mm->page_table_lock);
+		if (limit >= TASK_SIZE)
+			limit = -1UL;
+		current->mm->context.exec_limit = limit;
+	}
+	set_user_cs(&current->mm->context.user_cs, limit);
+
+	desc1 = &current->mm->context.user_cs;
+	desc2 = get_cpu_gdt_table(cpu) + GDT_ENTRY_DEFAULT_USER_CS;
+
+	if (__compare_user_cs_desc(desc1, desc2)) {
+		/*
+		 * The CS was not in sync - reload it and retry the
+		 * instruction. If the instruction still faults then
+		 * we won't hit this branch next time around.
+		 */
+		if (print_fatal_signals >= 2) {
+			printk(KERN_ERR "#GPF fixup (%ld[seg:%lx]) at %08lx, CPU#%d.\n",
+				error_code, error_code/8, regs->ip,
+				smp_processor_id());
+			printk(KERN_ERR "exec_limit: %08lx, user_cs: %08x/%08x, CPU_cs: %08x/%08x.\n",
+				current->mm->context.exec_limit,
+				desc1->a, desc1->b, desc2->a, desc2->b);
+		}
+
+		load_user_cs_desc(cpu, current->mm);
+
+		return 1;
+	}
+
+	return 0;
+}
+#endif
+
 static void __kprobes
 do_trap(int trapnr, int signr, char *str, struct pt_regs *regs,
 	long error_code, siginfo_t *info)
@@ -265,6 +337,29 @@ do_general_protection(struct pt_regs *regs, long error_code)
 	if (!user_mode(regs))
 		goto gp_in_kernel;
 
+#ifdef CONFIG_X86_32
+{
+	int cpu;
+	int ok;
+
+	cpu = get_cpu();
+	ok = check_lazy_exec_limit(cpu, regs, error_code);
+	put_cpu();
+
+	if (ok)
+		return;
+
+	if (print_fatal_signals) {
+		printk(KERN_ERR "#GPF(%ld[seg:%lx]) at %08lx, CPU#%d.\n",
+			error_code, error_code/8, regs->ip, smp_processor_id());
+		printk(KERN_ERR "exec_limit: %08lx, user_cs: %08x/%08x.\n",
+			current->mm->context.exec_limit,
+			current->mm->context.user_cs.a,
+			current->mm->context.user_cs.b);
+	}
+}
+#endif /*CONFIG_X86_32*/
+
 	tsk->thread.error_code = error_code;
 	tsk->thread.trap_no = 13;
 
@@ -801,19 +896,37 @@ do_device_not_available(struct pt_regs *regs, long error_code)
 }
 
 #ifdef CONFIG_X86_32
+/*
+ * The fixup code for errors in iret jumps to here (iret_exc). It loses
+ * the original trap number and erorr code. The bogus trap 32 and error
+ * code 0 are what the vanilla kernel delivers via:
+ * DO_ERROR_INFO(32, SIGSEGV, "iret exception", iret_error, ILL_BADSTK, 0, 1)
+ *
+ * NOTE: Because of the final "1" in the macro we need to enable interrupts.
+ *
+ * In case of a general protection fault in the iret instruction, we
+ * need to check for a lazy CS update for exec-shield.
+ */
 dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
 {
-	siginfo_t info;
+	int ok;
+	int cpu;
+
 	local_irq_enable();
 
-	info.si_signo = SIGILL;
-	info.si_errno = 0;
-	info.si_code = ILL_BADSTK;
-	info.si_addr = NULL;
-	if (notify_die(DIE_TRAP, "iret exception",
-			regs, error_code, 32, SIGILL) == NOTIFY_STOP)
-		return;
-	do_trap(32, SIGILL, "iret exception", regs, error_code, &info);
+	cpu = get_cpu();
+	ok = check_lazy_exec_limit(cpu, regs, error_code);
+	put_cpu();
+
+	if (!ok && notify_die(DIE_TRAP, "iret exception", regs,
+		error_code, 32, SIGSEGV) != NOTIFY_STOP) {
+			siginfo_t info;
+			info.si_signo = SIGSEGV;
+			info.si_errno = 0;
+			info.si_code = ILL_BADSTK;
+			info.si_addr = 0;
+			do_trap(32, SIGSEGV, "iret exception", regs, error_code, &info);
+	}
 }
 #endif