1 files changed, 251 insertions, 0 deletions
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
new file mode 100644
index 000000000..45f5d6cf6
--- /dev/null
+++ b/arch/x86/mm/extable.c
@@ -0,0 +1,251 @@
+#include <linux/extable.h>
+#include <linux/uaccess.h>
+#include <linux/sched/debug.h>
+#include <xen/xen.h>
+
+#include <asm/fpu/internal.h>
+#include <asm/traps.h>
+#include <asm/kdebug.h>
+
+typedef bool (*ex_handler_t)(const struct exception_table_entry *,
+			    struct pt_regs *, int);
+
+static inline unsigned long
+ex_fixup_addr(const struct exception_table_entry *x)
+{
+	return (unsigned long)&x->fixup + x->fixup;
+}
+static inline ex_handler_t
+ex_fixup_handler(const struct exception_table_entry *x)
+{
+	return (ex_handler_t)((unsigned long)&x->handler + x->handler);
+}
+
+__visible bool ex_handler_default(const struct exception_table_entry *fixup,
+				  struct pt_regs *regs, int trapnr)
+{
+	regs->ip = ex_fixup_addr(fixup);
+	return true;
+}
+EXPORT_SYMBOL(ex_handler_default);
+
+__visible bool ex_handler_fault(const struct exception_table_entry *fixup,
+				struct pt_regs *regs, int trapnr)
+{
+	regs->ip = ex_fixup_addr(fixup);
+	regs->ax = trapnr;
+	return true;
+}
+EXPORT_SYMBOL_GPL(ex_handler_fault);
+
+/*
+ * Handler for UD0 exception following a failed test against the
+ * result of a refcount inc/dec/add/sub.
+ */
+__visible bool ex_handler_refcount(const struct exception_table_entry *fixup,
+				   struct pt_regs *regs, int trapnr)
+{
+	/* First unconditionally saturate the refcount. */
+	*(int *)regs->cx = INT_MIN / 2;
+
+	/*
+	 * Strictly speaking, this reports the fixup destination, not
+	 * the fault location, and not the actually overflowing
+	 * instruction, which is the instruction before the "js", but
+	 * since that instruction could be a variety of lengths, just
+	 * report the location after the overflow, which should be close
+	 * enough for finding the overflow, as it's at least back in
+	 * the function, having returned from .text.unlikely.
+	 */
+	regs->ip = ex_fixup_addr(fixup);
+
+	/*
+	 * This function has been called because either a negative refcount
+	 * value was seen by any of the refcount functions, or a zero
+	 * refcount value was seen by refcount_dec().
+	 *
+	 * If we crossed from INT_MAX to INT_MIN, OF (Overflow Flag: result
+	 * wrapped around) will be set. Additionally, seeing the refcount
+	 * reach 0 will set ZF (Zero Flag: result was zero). In each of
+	 * these cases we want a report, since it's a boundary condition.
+	 * The SF case is not reported since it indicates post-boundary
+	 * manipulations below zero or above INT_MAX. And if none of the
+	 * flags are set, something has gone very wrong, so report it.
+	 */
+	if (regs->flags & (X86_EFLAGS_OF | X86_EFLAGS_ZF)) {
+		bool zero = regs->flags & X86_EFLAGS_ZF;
+
+		refcount_error_report(regs, zero ? "hit zero" : "overflow");
+	} else if ((regs->flags & X86_EFLAGS_SF) == 0) {
+		/* Report if none of OF, ZF, nor SF are set. */
+		refcount_error_report(regs, "unexpected saturation");
+	}
+
+	return true;
+}
+EXPORT_SYMBOL(ex_handler_refcount);
+
+/*
+ * Handler for when we fail to restore a task's FPU state.  We should never get
+ * here because the FPU state of a task using the FPU (task->thread.fpu.state)
+ * should always be valid.  However, past bugs have allowed userspace to set
+ * reserved bits in the XSAVE area using PTRACE_SETREGSET or sys_rt_sigreturn().
+ * These caused XRSTOR to fail when switching to the task, leaking the FPU
+ * registers of the task previously executing on the CPU.  Mitigate this class
+ * of vulnerability by restoring from the initial state (essentially, zeroing
+ * out all the FPU registers) if we can't restore from the task's FPU state.
+ */
+__visible bool ex_handler_fprestore(const struct exception_table_entry *fixup,
+				    struct pt_regs *regs, int trapnr)
+{
+	regs->ip = ex_fixup_addr(fixup);
+
+	WARN_ONCE(1, "Bad FPU state detected at %pB, reinitializing FPU registers.",
+		  (void *)instruction_pointer(regs));
+
+	__copy_kernel_to_fpregs(&init_fpstate, -1);
+	return true;
+}
+EXPORT_SYMBOL_GPL(ex_handler_fprestore);
+
+__visible bool ex_handler_ext(const struct exception_table_entry *fixup,
+			      struct pt_regs *regs, int trapnr)
+{
+	/* Special hack for uaccess_err */
+	current->thread.uaccess_err = 1;
+	regs->ip = ex_fixup_addr(fixup);
+	return true;
+}
+EXPORT_SYMBOL(ex_handler_ext);
+
+__visible bool ex_handler_rdmsr_unsafe(const struct exception_table_entry *fixup,
+				       struct pt_regs *regs, int trapnr)
+{
+	if (pr_warn_once("unchecked MSR access error: RDMSR from 0x%x at rIP: 0x%lx (%pF)\n",
+			 (unsigned int)regs->cx, regs->ip, (void *)regs->ip))
+		show_stack_regs(regs);
+
+	/* Pretend that the read succeeded and returned 0. */
+	regs->ip = ex_fixup_addr(fixup);
+	regs->ax = 0;
+	regs->dx = 0;
+	return true;
+}
+EXPORT_SYMBOL(ex_handler_rdmsr_unsafe);
+
+__visible bool ex_handler_wrmsr_unsafe(const struct exception_table_entry *fixup,
+				       struct pt_regs *regs, int trapnr)
+{
+	if (pr_warn_once("unchecked MSR access error: WRMSR to 0x%x (tried to write 0x%08x%08x) at rIP: 0x%lx (%pF)\n",
+			 (unsigned int)regs->cx, (unsigned int)regs->dx,
+			 (unsigned int)regs->ax,  regs->ip, (void *)regs->ip))
+		show_stack_regs(regs);
+
+	/* Pretend that the write succeeded. */
+	regs->ip = ex_fixup_addr(fixup);
+	return true;
+}
+EXPORT_SYMBOL(ex_handler_wrmsr_unsafe);
+
+__visible bool ex_handler_clear_fs(const struct exception_table_entry *fixup,
+				   struct pt_regs *regs, int trapnr)
+{
+	if (static_cpu_has(X86_BUG_NULL_SEG))
+		asm volatile ("mov %0, %%fs" : : "rm" (__USER_DS));
+	asm volatile ("mov %0, %%fs" : : "rm" (0));
+	return ex_handler_default(fixup, regs, trapnr);
+}
+EXPORT_SYMBOL(ex_handler_clear_fs);
+
+__visible bool ex_has_fault_handler(unsigned long ip)
+{
+	const struct exception_table_entry *e;
+	ex_handler_t handler;
+
+	e = search_exception_tables(ip);
+	if (!e)
+		return false;
+	handler = ex_fixup_handler(e);
+
+	return handler == ex_handler_fault;
+}
+
+int fixup_exception(struct pt_regs *regs, int trapnr)
+{
+	const struct exception_table_entry *e;
+	ex_handler_t handler;
+
+#ifdef CONFIG_PNPBIOS
+	if (unlikely(SEGMENT_IS_PNP_CODE(regs->cs))) {
+		extern u32 pnp_bios_fault_eip, pnp_bios_fault_esp;
+		extern u32 pnp_bios_is_utter_crap;
+		pnp_bios_is_utter_crap = 1;
+		printk(KERN_CRIT "PNPBIOS fault.. attempting recovery.\n");
+		__asm__ volatile(
+			"movl %0, %%esp\n\t"
+			"jmp *%1\n\t"
+			: : "g" (pnp_bios_fault_esp), "g" (pnp_bios_fault_eip));
+		panic("do_trap: can't hit this");
+	}
+#endif
+
+	e = search_exception_tables(regs->ip);
+	if (!e)
+		return 0;
+
+	handler = ex_fixup_handler(e);
+	return handler(e, regs, trapnr);
+}
+
+extern unsigned int early_recursion_flag;
+
+/* Restricted version used during very early boot */
+void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
+{
+	/* Ignore early NMIs. */
+	if (trapnr == X86_TRAP_NMI)
+		return;
+
+	if (early_recursion_flag > 2)
+		goto halt_loop;
+
+	/*
+	 * Old CPUs leave the high bits of CS on the stack
+	 * undefined.  I'm not sure which CPUs do this, but at least
+	 * the 486 DX works this way.
+	 * Xen pv domains are not using the default __KERNEL_CS.
+	 */
+	if (!xen_pv_domain() && regs->cs != __KERNEL_CS)
+		goto fail;
+
+	/*
+	 * The full exception fixup machinery is available as soon as
+	 * the early IDT is loaded.  This means that it is the
+	 * responsibility of extable users to either function correctly
+	 * when handlers are invoked early or to simply avoid causing
+	 * exceptions before they're ready to handle them.
+	 *
+	 * This is better than filtering which handlers can be used,
+	 * because refusing to call a handler here is guaranteed to
+	 * result in a hard-to-debug panic.
+	 *
+	 * Keep in mind that not all vectors actually get here.  Early
+	 * fage faults, for example, are special.
+	 */
+	if (fixup_exception(regs, trapnr))
+		return;
+
+	if (fixup_bug(regs, trapnr))
+		return;
+
+fail:
+	early_printk("PANIC: early exception 0x%02x IP %lx:%lx error %lx cr2 0x%lx\n",
+		     (unsigned)trapnr, (unsigned long)regs->cs, regs->ip,
+		     regs->orig_ax, read_cr2());
+
+	show_regs(regs);
+
+halt_loop:
+	while (true)
+		halt();
+}