x86/mm: Expand the exception table logic to allow new handling options

Huge amounts of help from  Andy Lutomirski and Borislav Petkov to
produce this. Andy provided the inspiration to add classes to the
exception table with a clever bit-squeezing trick, Boris pointed
out how much cleaner it would all be if we just had a new field.

Linus Torvalds blessed the expansion with:

  ' I'd rather not be clever in order to save just a tiny amount of space
    in the exception table, which isn't really criticial for anybody. '

The third field is another relative function pointer, this one to a
handler that executes the actions.

We start out with three handlers:

 1: Legacy - just jumps the to fixup IP
 2: Fault - provide the trap number in %ax to the fixup code
 3: Cleaned up legacy for the uaccess error hack

Signed-off-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/f6af78fcbd348cf4939875cfda9c19689b5e50b8.1455732970.git.tony.luck@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 4 insertions, 4 deletions

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 1deffe6cc873..0f05deeff5ce 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -988,7 +988,7 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
                  * In case the user-specified fault handler returned
                  * zero, try to fix up.
                  */
-                if (fixup_exception(regs))
+                if (fixup_exception(regs, trapnr))
                         return 1;
 
                 /*
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index ade185a46b1d..211c11c7bba4 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -199,7 +199,7 @@ do_trap_no_signal(struct task_struct *tsk, int trapnr, char *str,
         }
 
         if (!user_mode(regs)) {
-                if (!fixup_exception(regs)) {
+                if (!fixup_exception(regs, trapnr)) {
                         tsk->thread.error_code = error_code;
                         tsk->thread.trap_nr = trapnr;
                         die(str, regs, error_code);
@@ -453,7 +453,7 @@ do_general_protection(struct pt_regs *regs, long error_code)
 
         tsk = current;
         if (!user_mode(regs)) {
-                if (fixup_exception(regs))
+                if (fixup_exception(regs, X86_TRAP_GP))
                         return;
 
                 tsk->thread.error_code = error_code;
@@ -699,7 +699,7 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
         conditional_sti(regs);
 
         if (!user_mode(regs)) {
-                if (!fixup_exception(regs)) {
+                if (!fixup_exception(regs, trapnr)) {
                         task->thread.error_code = error_code;
                         task->thread.trap_nr = trapnr;
                         die(str, regs, error_code);