1 files changed, 54 insertions, 17 deletions

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 0d0e922fafc1..de801f22128a 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -233,32 +233,40 @@ DO_ERROR(X86_TRAP_UD,     SIGILL,  "invalid opcode",		invalid_op)
 DO_ERROR(X86_TRAP_OLD_MF, SIGFPE,  "coprocessor segment overrun",coprocessor_segment_overrun)
 DO_ERROR(X86_TRAP_TS,     SIGSEGV, "invalid TSS",               invalid_TSS)
 DO_ERROR(X86_TRAP_NP,     SIGBUS,  "segment not present",       segment_not_present)
-#ifdef CONFIG_X86_32
 DO_ERROR(X86_TRAP_SS,     SIGBUS,  "stack segment",             stack_segment)
-#endif
 DO_ERROR(X86_TRAP_AC,     SIGBUS,  "alignment check",           alignment_check)
 
 #ifdef CONFIG_X86_64
 /* Runs on IST stack */
-dotraplinkage void do_stack_segment(struct pt_regs *regs, long error_code)
-{
-        enum ctx_state prev_state;
-
-        prev_state = exception_enter();
-        if (notify_die(DIE_TRAP, "stack segment", regs, error_code,
-                       X86_TRAP_SS, SIGBUS) != NOTIFY_STOP) {
-                preempt_conditional_sti(regs);
-                do_trap(X86_TRAP_SS, SIGBUS, "stack segment", regs, error_code, NULL);
-                preempt_conditional_cli(regs);
-        }
-        exception_exit(prev_state);
-}
-
 dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
 {
         static const char str[] = "double fault";
         struct task_struct *tsk = current;
 
+#ifdef CONFIG_X86_ESPFIX64
+        extern unsigned char native_irq_return_iret[];
+
+        /*
+         * If IRET takes a non-IST fault on the espfix64 stack, then we
+         * end up promoting it to a doublefault.  In that case, modify
+         * the stack to make it look like we just entered the #GP
+         * handler from user space, similar to bad_iret.
+         */
+        if (((long)regs->sp >> PGDIR_SHIFT) == ESPFIX_PGD_ENTRY &&
+                regs->cs == __KERNEL_CS &&
+                regs->ip == (unsigned long)native_irq_return_iret)
+        {
+                struct pt_regs *normal_regs = task_pt_regs(current);
+
+                /* Fake a #GP(0) from userspace. */
+                memmove(&normal_regs->ip, (void *)regs->sp, 5*8);
+                normal_regs->orig_ax = 0;  /* Missing (lost) #GP error code */
+                regs->ip = (unsigned long)general_protection;
+                regs->sp = (unsigned long)&normal_regs->orig_ax;
+                return;
+        }
+#endif
+
         exception_enter();
         /* Return not checked because double check cannot be ignored */
         notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);
@@ -399,6 +407,35 @@ asmlinkage __visible struct pt_regs *sync_regs(struct pt_regs *eregs)
         return regs;
 }
 NOKPROBE_SYMBOL(sync_regs);
+
+struct bad_iret_stack {
+        void *error_entry_ret;
+        struct pt_regs regs;
+};
+
+asmlinkage __visible
+struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
+{
+        /*
+         * This is called from entry_64.S early in handling a fault
+         * caused by a bad iret to user mode.  To handle the fault
+         * correctly, we want move our stack frame to task_pt_regs
+         * and we want to pretend that the exception came from the
+         * iret target.
+         */
+        struct bad_iret_stack *new_stack =
+                container_of(task_pt_regs(current),
+                             struct bad_iret_stack, regs);
+
+        /* Copy the IRET target to the new stack. */
+        memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);
+
+        /* Copy the remainder of the stack from the current stack. */
+        memmove(new_stack, s, offsetof(struct bad_iret_stack, regs.ip));
+
+        BUG_ON(!user_mode_vm(&new_stack->regs));
+        return new_stack;
+}
 #endif
 
 /*
@@ -778,7 +815,7 @@ void __init trap_init(void)
         set_intr_gate(X86_TRAP_OLD_MF, coprocessor_segment_overrun);
         set_intr_gate(X86_TRAP_TS, invalid_TSS);
         set_intr_gate(X86_TRAP_NP, segment_not_present);
-        set_intr_gate_ist(X86_TRAP_SS, &stack_segment, STACKFAULT_STACK);
+        set_intr_gate(X86_TRAP_SS, stack_segment);
         set_intr_gate(X86_TRAP_GP, general_protection);
         set_intr_gate(X86_TRAP_SPURIOUS, spurious_interrupt_bug);
         set_intr_gate(X86_TRAP_MF, coprocessor_error);