Merge branch 'WIP.x86-pti.entry-for-linus' of git://git.kernel.org/pub/scm/linux...

[sfrench/cifs-2.6.git] / arch / x86 / kernel / traps.c

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 989514c94a55d8fa93a07192edd199be1a607bf8..e98f8b66a460b98b31d262cff23fa063be33ac5a 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -348,9 +348,15 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
 
        /*
         * 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.
+        * end up promoting it to a doublefault.  In that case, take
+        * advantage of the fact that we're not using the normal (TSS.sp0)
+        * stack right now.  We can write a fake #GP(0) frame at TSS.sp0
+        * and then modify our own IRET frame so that, when we return,
+        * we land directly at the #GP(0) vector with the stack already
+        * set up according to its expectations.
+        *
+        * The net result is that our #GP handler will think that we
+        * entered from usermode with the bad user context.
         *
         * No need for ist_enter here because we don't use RCU.
         */
@@ -358,13 +364,26 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
                regs->cs == __KERNEL_CS &&
                regs->ip == (unsigned long)native_irq_return_iret)
        {
-               struct pt_regs *normal_regs = task_pt_regs(current);
+               struct pt_regs *gpregs = (struct pt_regs *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
 
-               /* 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->sp points to the failing IRET frame on the
+                * ESPFIX64 stack.  Copy it to the entry stack.  This fills
+                * in gpregs->ss through gpregs->ip.
+                *
+                */
+               memmove(&gpregs->ip, (void *)regs->sp, 5*8);
+               gpregs->orig_ax = 0;  /* Missing (lost) #GP error code */
+
+               /*
+                * Adjust our frame so that we return straight to the #GP
+                * vector with the expected RSP value.  This is safe because
+                * we won't enable interupts or schedule before we invoke
+                * general_protection, so nothing will clobber the stack
+                * frame we just set up.
+                */
                regs->ip = (unsigned long)general_protection;
-               regs->sp = (unsigned long)&normal_regs->orig_ax;
+               regs->sp = (unsigned long)&gpregs->orig_ax;
 
                return;
        }
@@ -389,7 +408,7 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
         *
         *   Processors update CR2 whenever a page fault is detected. If a
         *   second page fault occurs while an earlier page fault is being
-        *   deliv- ered, the faulting linear address of the second fault will
+        *   delivered, the faulting linear address of the second fault will
         *   overwrite the contents of CR2 (replacing the previous
         *   address). These updates to CR2 occur even if the page fault
         *   results in a double fault or occurs during the delivery of a
@@ -605,14 +624,15 @@ NOKPROBE_SYMBOL(do_int3);
 
 #ifdef CONFIG_X86_64
 /*
- * Help handler running on IST stack to switch off the IST stack if the
- * interrupted code was in user mode. The actual stack switch is done in
- * entry_64.S
+ * Help handler running on a per-cpu (IST or entry trampoline) stack
+ * to switch to the normal thread stack if the interrupted code was in
+ * user mode. The actual stack switch is done in entry_64.S
  */
 asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs)
 {
-       struct pt_regs *regs = task_pt_regs(current);
-       *regs = *eregs;
+       struct pt_regs *regs = (struct pt_regs *)this_cpu_read(cpu_current_top_of_stack) - 1;
+       if (regs != eregs)
+               *regs = *eregs;
        return regs;
 }
 NOKPROBE_SYMBOL(sync_regs);
@@ -628,13 +648,13 @@ 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.
+        * correctly, we want to move our stack frame to where it would
+        * be had we entered directly on the entry stack (rather than
+        * just below the IRET frame) 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);
+               (struct bad_iret_stack *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
 
        /* Copy the IRET target to the new stack. */
        memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);
@@ -795,14 +815,6 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code)
        debug_stack_usage_dec();
 
 exit:
-#if defined(CONFIG_X86_32)
-       /*
-        * This is the most likely code path that involves non-trivial use
-        * of the SYSENTER stack.  Check that we haven't overrun it.
-        */
-       WARN(this_cpu_read(cpu_tss.SYSENTER_stack_canary) != STACK_END_MAGIC,
-            "Overran or corrupted SYSENTER stack\n");
-#endif
        ist_exit(regs);
 }
 NOKPROBE_SYMBOL(do_debug);
@@ -929,6 +941,9 @@ dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
 
 void __init trap_init(void)
 {
+       /* Init cpu_entry_area before IST entries are set up */
+       setup_cpu_entry_areas();
+
        idt_setup_traps();
 
        /*