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

This reverts commit fcf5e5198b447969ed2a56ec335dae3c695a6b46 which is
548acf19234dbda5a52d5a8e7e205af46e9da840 upstream.

Cc: Tony Luck <tony.luck@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

6 files changed, 57 insertions, 109 deletions

diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index f5063b6659eb..189679aba703 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -44,22 +44,19 @@
 
 /* Exception table entry */
 #ifdef __ASSEMBLY__
-# define _ASM_EXTABLE_HANDLE(from, to, handler)			\
+# define _ASM_EXTABLE(from,to)					\
 	.pushsection "__ex_table","a" ;				\
-	.balign 4 ;						\
+	.balign 8 ;						\
 	.long (from) - . ;					\
 	.long (to) - . ;					\
-	.long (handler) - . ;					\
 	.popsection
 
-# define _ASM_EXTABLE(from, to)					\
-	_ASM_EXTABLE_HANDLE(from, to, ex_handler_default)
-
-# define _ASM_EXTABLE_FAULT(from, to)				\
-	_ASM_EXTABLE_HANDLE(from, to, ex_handler_fault)
-
-# define _ASM_EXTABLE_EX(from, to)				\
-	_ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
+# define _ASM_EXTABLE_EX(from,to)				\
+	.pushsection "__ex_table","a" ;				\
+	.balign 8 ;						\
+	.long (from) - . ;					\
+	.long (to) - . + 0x7ffffff0 ;				\
+	.popsection
 
 # define _ASM_NOKPROBE(entry)					\
 	.pushsection "_kprobe_blacklist","aw" ;			\
@@ -92,24 +89,19 @@
 	.endm
 
 #else
-# define _EXPAND_EXTABLE_HANDLE(x) #x
-# define _ASM_EXTABLE_HANDLE(from, to, handler)			\
+# define _ASM_EXTABLE(from,to)					\
 	" .pushsection \"__ex_table\",\"a\"\n"			\
-	" .balign 4\n"						\
+	" .balign 8\n"						\
 	" .long (" #from ") - .\n"				\
 	" .long (" #to ") - .\n"				\
-	" .long (" _EXPAND_EXTABLE_HANDLE(handler) ") - .\n"	\
 	" .popsection\n"
 
-# define _ASM_EXTABLE(from, to)					\
-	_ASM_EXTABLE_HANDLE(from, to, ex_handler_default)
-
-# define _ASM_EXTABLE_FAULT(from, to)				\
-	_ASM_EXTABLE_HANDLE(from, to, ex_handler_fault)
-
-# define _ASM_EXTABLE_EX(from, to)				\
-	_ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
-
+# define _ASM_EXTABLE_EX(from,to)				\
+	" .pushsection \"__ex_table\",\"a\"\n"			\
+	" .balign 8\n"						\
+	" .long (" #from ") - .\n"				\
+	" .long (" #to ") - . + 0x7ffffff0\n"			\
+	" .popsection\n"
 /* For C file, we already have NOKPROBE_SYMBOL macro */
 #endif
 
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 3794c7331cfc..d42252ce9b4d 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -90,11 +90,12 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
 	likely(!__range_not_ok(addr, size, user_addr_max()))
 
 /*
- * The exception table consists of triples of addresses relative to the
- * exception table entry itself. The first address is of an instruction
- * that is allowed to fault, the second is the target at which the program
- * should continue. The third is a handler function to deal with the fault
- * caused by the instruction in the first field.
+ * The exception table consists of pairs of addresses relative to the
+ * exception table enty itself: the first is the address of an
+ * instruction that is allowed to fault, and the second is the address
+ * at which the program should continue.  No registers are modified,
+ * so it is entirely up to the continuation code to figure out what to
+ * do.
  *
  * All the routines below use bits of fixup code that are out of line
  * with the main instruction path.  This means when everything is well,
@@ -103,14 +104,13 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
  */
 
 struct exception_table_entry {
-	int insn, fixup, handler;
+	int insn, fixup;
 };
 /* This is not the generic standard exception_table_entry format */
 #define ARCH_HAS_SORT_EXTABLE
 #define ARCH_HAS_SEARCH_EXTABLE
 
-extern int fixup_exception(struct pt_regs *regs, int trapnr);
-extern bool ex_has_fault_handler(unsigned long ip);
+extern int fixup_exception(struct pt_regs *regs);
 extern int early_fixup_exception(unsigned long *ip);
 
 /*
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index e1d1f6cbaf11..023c442c33bb 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -1000,7 +1000,7 @@ 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, trapnr))
+		if (fixup_exception(regs))
 			return 1;
 
 		/*
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 5621f882645e..679302c312f8 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, trapnr)) {
+		if (!fixup_exception(regs)) {
 			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, X86_TRAP_GP))
+		if (fixup_exception(regs))
 			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, trapnr)) {
+		if (!fixup_exception(regs)) {
 			task->thread.error_code = error_code;
 			task->thread.trap_nr = trapnr;
 			die(str, regs, error_code);
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 9dd7e4b7fcde..903ec1e9c326 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -3,9 +3,6 @@
 #include <linux/sort.h>
 #include <asm/uaccess.h>
 
-typedef bool (*ex_handler_t)(const struct exception_table_entry *,
-			    struct pt_regs *, int);
-
 static inline unsigned long
 ex_insn_addr(const struct exception_table_entry *x)
 {
@@ -16,56 +13,11 @@ 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);
-}
-
-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);
-
-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);
-
-bool ex_handler_ext(const struct exception_table_entry *fixup,
-		   struct pt_regs *regs, int trapnr)
-{
-	/* Special hack for uaccess_err */
-	current_thread_info()->uaccess_err = 1;
-	regs->ip = ex_fixup_addr(fixup);
-	return true;
-}
-EXPORT_SYMBOL(ex_handler_ext);
-
-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)
+int fixup_exception(struct pt_regs *regs)
 {
-	const struct exception_table_entry *e;
-	ex_handler_t handler;
+	const struct exception_table_entry *fixup;
+	unsigned long new_ip;
 
 #ifdef CONFIG_PNPBIOS
 	if (unlikely(SEGMENT_IS_PNP_CODE(regs->cs))) {
@@ -81,34 +33,42 @@ int fixup_exception(struct pt_regs *regs, int trapnr)
 	}
 #endif
 
-	e = search_exception_tables(regs->ip);
-	if (!e)
-		return 0;
+	fixup = search_exception_tables(regs->ip);
+	if (fixup) {
+		new_ip = ex_fixup_addr(fixup);
+
+		if (fixup->fixup - fixup->insn >= 0x7ffffff0 - 4) {
+			/* Special hack for uaccess_err */
+			current_thread_info()->uaccess_err = 1;
+			new_ip -= 0x7ffffff0;
+		}
+		regs->ip = new_ip;
+		return 1;
+	}
 
-	handler = ex_fixup_handler(e);
-	return handler(e, regs, trapnr);
+	return 0;
 }
 
 /* Restricted version used during very early boot */
 int __init early_fixup_exception(unsigned long *ip)
 {
-	const struct exception_table_entry *e;
+	const struct exception_table_entry *fixup;
 	unsigned long new_ip;
-	ex_handler_t handler;
 
-	e = search_exception_tables(*ip);
-	if (!e)
-		return 0;
+	fixup = search_exception_tables(*ip);
+	if (fixup) {
+		new_ip = ex_fixup_addr(fixup);
 
-	new_ip  = ex_fixup_addr(e);
-	handler = ex_fixup_handler(e);
+		if (fixup->fixup - fixup->insn >= 0x7ffffff0 - 4) {
+			/* uaccess handling not supported during early boot */
+			return 0;
+		}
 
-	/* special handling not supported during early boot */
-	if (handler != ex_handler_default)
-		return 0;
+		*ip = new_ip;
+		return 1;
+	}
 
-	*ip = new_ip;
-	return 1;
+	return 0;
 }
 
 /*
@@ -173,8 +133,6 @@ void sort_extable(struct exception_table_entry *start,
 		i += 4;
 		p->fixup += i;
 		i += 4;
-		p->handler += i;
-		i += 4;
 	}
 
 	sort(start, finish - start, sizeof(struct exception_table_entry),
@@ -187,8 +145,6 @@ void sort_extable(struct exception_table_entry *start,
 		i += 4;
 		p->fixup -= i;
 		i += 4;
-		p->handler -= i;
-		i += 4;
 	}
 }
 
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 03898aea6e0f..e830c71a1323 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -663,7 +663,7 @@ no_context(struct pt_regs *regs, unsigned long error_code,
 	int sig;
 
 	/* Are we prepared to handle this kernel fault? */
-	if (fixup_exception(regs, X86_TRAP_PF)) {
+	if (fixup_exception(regs)) {
 		/*
 		 * Any interrupt that takes a fault gets the fixup. This makes
 		 * the below recursive fault logic only apply to a faults from