[PATCH] x86_64: Regularize exception stack handling

This fixes various issues in the return path for "paranoid"
handlers (= running on a private exception stack that act like NMIs).

Generalize previous hack to switch back to process stack for
scheduling/signal handling purposes.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 28 insertions, 29 deletions

diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
index 09e4a6460e74..1b06ab24538b 100644
--- a/arch/x86_64/kernel/traps.c
+++ b/arch/x86_64/kernel/traps.c
@@ -488,24 +488,8 @@ DO_ERROR(10, SIGSEGV, "invalid TSS", invalid_TSS)
 DO_ERROR(11, SIGBUS,  "segment not present", segment_not_present)
 DO_ERROR_INFO(17, SIGBUS, "alignment check", alignment_check, BUS_ADRALN, 0)
 DO_ERROR(18, SIGSEGV, "reserved", reserved)
-
-#define DO_ERROR_STACK(trapnr, signr, str, name) \
-asmlinkage void *do_##name(struct pt_regs * regs, long error_code) \
-{ \
-        struct pt_regs *pr = ((struct pt_regs *)(current->thread.rsp0))-1; \
-        if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) \
-                                                        == NOTIFY_STOP) \
-                return regs; \
-        if (regs->cs & 3) { \
-                memcpy(pr, regs, sizeof(struct pt_regs)); \
-                regs = pr; \
-        } \
-        do_trap(trapnr, signr, str, regs, error_code, NULL); \
-        return regs;            \
-}
-
-DO_ERROR_STACK(12, SIGBUS,  "stack segment", stack_segment)
-DO_ERROR_STACK( 8, SIGSEGV, "double fault", double_fault)
+DO_ERROR(12, SIGBUS,  "stack segment", stack_segment)
+DO_ERROR( 8, SIGSEGV, "double fault", double_fault)
 
 asmlinkage void do_general_protection(struct pt_regs * regs, long error_code)
 {
@@ -584,6 +568,8 @@ static void unknown_nmi_error(unsigned char reason, struct pt_regs * regs)
         printk("Do you have a strange power saving mode enabled?\n");
 }
 
+/* Runs on IST stack. This code must keep interrupts off all the time.
+   Nested NMIs are prevented by the CPU. */
 asmlinkage void default_do_nmi(struct pt_regs *regs)
 {
         unsigned char reason = 0;
@@ -629,20 +615,34 @@ asmlinkage void do_int3(struct pt_regs * regs, long error_code)
         return;
 }
 
+/* Help handler running on IST stack to switch back to user stack
+   for scheduling or signal handling. The actual stack switch is done in
+   entry.S */
+asmlinkage struct pt_regs *sync_regs(struct pt_regs *eregs)
+{
+        struct pt_regs *regs = eregs;
+        /* Did already sync */
+        if (eregs == (struct pt_regs *)eregs->rsp)
+                ;
+        /* Exception from user space */
+        else if (eregs->cs & 3)
+                regs = ((struct pt_regs *)current->thread.rsp0) - 1;
+        /* Exception from kernel and interrupts are enabled. Move to
+           kernel process stack. */
+        else if (eregs->eflags & X86_EFLAGS_IF)
+                regs = (struct pt_regs *)(eregs->rsp -= sizeof(struct pt_regs));
+        if (eregs != regs)
+                *regs = *eregs;
+        return regs;
+}
+
 /* runs on IST stack. */
-asmlinkage void *do_debug(struct pt_regs * regs, unsigned long error_code)
+asmlinkage void do_debug(struct pt_regs * regs, unsigned long error_code)
 {
-        struct pt_regs *pr;
         unsigned long condition;
         struct task_struct *tsk = current;
         siginfo_t info;
 
-        pr = (struct pt_regs *)(current->thread.rsp0)-1;
-        if (regs->cs & 3) {
-                memcpy(pr, regs, sizeof(struct pt_regs));
-                regs = pr;
-        }       
-
 #ifdef CONFIG_CHECKING
        { 
                /* RED-PEN interaction with debugger - could destroy gs */
@@ -660,7 +660,7 @@ asmlinkage void *do_debug(struct pt_regs * regs, unsigned long error_code)
 
         if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
                                                 SIGTRAP) == NOTIFY_STOP) {
-                return regs;
+                return;
         }
         conditional_sti(regs);
 
@@ -712,7 +712,7 @@ asmlinkage void *do_debug(struct pt_regs * regs, unsigned long error_code)
 clear_dr7:
         asm volatile("movq %0,%%db7"::"r"(0UL));
         notify_die(DIE_DEBUG, "debug", regs, condition, 1, SIGTRAP);
-        return regs;
+        return;
 
 clear_TF_reenable:
         set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
@@ -722,7 +722,6 @@ clear_TF:
         if (notify_die(DIE_DEBUG, "debug2", regs, condition, 1, SIGTRAP) 
                                                                 != NOTIFY_STOP)
         regs->eflags &= ~TF_MASK;
-        return regs;    
 }
 
 static int kernel_math_error(struct pt_regs *regs, char *str)