x86/mm: Expand the exception table logic to allow new handling options (548acf19) · Commits · e / devices / android_kernel_teracube_mt6765

Documentation/x86/exception-tables.txt

+35 −0

Original line number	Original line	Diff line number	Diff line
	@@ -290,3 +290,38 @@ Due to the way that the exception table is built and needs to be ordered,
	only use exceptions for code in the .text section. Any other section		only use exceptions for code in the .text section. Any other section
	will cause the exception table to not be sorted correctly, and the		will cause the exception table to not be sorted correctly, and the
	exceptions will fail.		exceptions will fail.

			Things changed when 64-bit support was added to x86 Linux. Rather than
			double the size of the exception table by expanding the two entries
			from 32-bits to 64 bits, a clever trick was used to store addresses
			as relative offsets from the table itself. The assembly code changed
			from:
			.long 1b,3b
			to:
			.long (from) - .
			.long (to) - .

			and the C-code that uses these values converts back to absolute addresses
			like this:

			ex_insn_addr(const struct exception_table_entry *x)
			{
			return (unsigned long)&x->insn + x->insn;
			}

			In v4.6 the exception table entry was expanded with a new field "handler".
			This is also 32-bits wide and contains a third relative function
			pointer which points to one of:

			1) int ex_handler_default(const struct exception_table_entry *fixup)
			This is legacy case that just jumps to the fixup code
			2) int ex_handler_fault(const struct exception_table_entry *fixup)
			This case provides the fault number of the trap that occurred at
			entry->insn. It is used to distinguish page faults from machine
			check.
			3) int ex_handler_ext(const struct exception_table_entry *fixup)
			This case is used for uaccess_err ... we need to set a flag
			in the task structure. Before the handler functions existed this
			case was handled by adding a large offset to the fixup to tag
			it as special.
			More functions can easily be added.

arch/x86/include/asm/asm.h

+24 −16

Original line number	Original line	Diff line number	Diff line
	@@ -44,19 +44,22 @@

	/* Exception table entry */		/* Exception table entry */
	#ifdef __ASSEMBLY__		#ifdef __ASSEMBLY__
	# define _ASM_EXTABLE(from,to) \		# define _ASM_EXTABLE_HANDLE(from, to, handler) \
	.pushsection "__ex_table","a" ; \		.pushsection "__ex_table","a" ; \
	.balign 8 ; \		.balign 4 ; \
	.long (from) - . ; \		.long (from) - . ; \
	.long (to) - . ; \		.long (to) - . ; \
			.long (handler) - . ; \
	.popsection		.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) \		# define _ASM_EXTABLE_EX(from, to) \
	.pushsection "__ex_table","a" ; \		_ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
	.balign 8 ; \
	.long (from) - . ; \
	.long (to) - . + 0x7ffffff0 ; \
	.popsection

	# define _ASM_NOKPROBE(entry) \		# define _ASM_NOKPROBE(entry) \
	.pushsection "_kprobe_blacklist","aw" ; \		.pushsection "_kprobe_blacklist","aw" ; \
	@@ -89,19 +92,24 @@
	.endm		.endm

	#else		#else
	# define _ASM_EXTABLE(from,to) \		# define _EXPAND_EXTABLE_HANDLE(x) #x
			# define _ASM_EXTABLE_HANDLE(from, to, handler) \
	" .pushsection \"__ex_table\",\"a\"\n" \		" .pushsection \"__ex_table\",\"a\"\n" \
	" .balign 8\n" \		" .balign 4\n" \
	" .long (" #from ") - .\n" \		" .long (" #from ") - .\n" \
	" .long (" #to ") - .\n" \		" .long (" #to ") - .\n" \
			" .long (" _EXPAND_EXTABLE_HANDLE(handler) ") - .\n" \
	" .popsection\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) \		# define _ASM_EXTABLE_EX(from, to) \
	" .pushsection \"__ex_table\",\"a\"\n" \		_ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
	" .balign 8\n" \
	" .long (" #from ") - .\n" \
	" .long (" #to ") - . + 0x7ffffff0\n" \
	" .popsection\n"
	/* For C file, we already have NOKPROBE_SYMBOL macro */		/* For C file, we already have NOKPROBE_SYMBOL macro */
	#endif		#endif

arch/x86/include/asm/uaccess.h

+8 −8

Original line number	Original line	Diff line number	Diff line
	@@ -90,12 +90,11 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
	likely(!__range_not_ok(addr, size, user_addr_max()))		likely(!__range_not_ok(addr, size, user_addr_max()))

	/*		/*
	* The exception table consists of pairs of addresses relative to the		* The exception table consists of triples of addresses relative to the
	* exception table enty itself: the first is the address of an		* exception table entry itself. The first address is of an instruction
	* instruction that is allowed to fault, and the second is the address		* that is allowed to fault, the second is the target at which the program
	* at which the program should continue. No registers are modified,		* should continue. The third is a handler function to deal with the fault
	* so it is entirely up to the continuation code to figure out what to		* caused by the instruction in the first field.
	* do.
	*		*
	* All the routines below use bits of fixup code that are out of line		* 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,		* with the main instruction path. This means when everything is well,
	@@ -104,13 +103,14 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
	*/		*/

	struct exception_table_entry {		struct exception_table_entry {
	int insn, fixup;		int insn, fixup, handler;
	};		};
	/* This is not the generic standard exception_table_entry format */		/* This is not the generic standard exception_table_entry format */
	#define ARCH_HAS_SORT_EXTABLE		#define ARCH_HAS_SORT_EXTABLE
	#define ARCH_HAS_SEARCH_EXTABLE		#define ARCH_HAS_SEARCH_EXTABLE

	extern int fixup_exception(struct pt_regs *regs);		extern int fixup_exception(struct pt_regs *regs, int trapnr);
			extern bool ex_has_fault_handler(unsigned long ip);
	extern int early_fixup_exception(unsigned long *ip);		extern int early_fixup_exception(unsigned long *ip);

	/*		/*

arch/x86/kernel/kprobes/core.c

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -988,7 +988,7 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
	* In case the user-specified fault handler returned		* In case the user-specified fault handler returned
	* zero, try to fix up.		* zero, try to fix up.
	*/		*/
	if (fixup_exception(regs))		if (fixup_exception(regs, trapnr))
	return 1;		return 1;

	/*		/*

arch/x86/kernel/traps.c

+3 −3

Original line number	Original line	Diff line number	Diff line
	@@ -199,7 +199,7 @@ do_trap_no_signal(struct task_struct tsk, int trapnr, char str,
	}		}

	if (!user_mode(regs)) {		if (!user_mode(regs)) {
	if (!fixup_exception(regs)) {		if (!fixup_exception(regs, trapnr)) {
	tsk->thread.error_code = error_code;		tsk->thread.error_code = error_code;
	tsk->thread.trap_nr = trapnr;		tsk->thread.trap_nr = trapnr;
	die(str, regs, error_code);		die(str, regs, error_code);
	@@ -453,7 +453,7 @@ do_general_protection(struct pt_regs *regs, long error_code)

	tsk = current;		tsk = current;
	if (!user_mode(regs)) {		if (!user_mode(regs)) {
	if (fixup_exception(regs))		if (fixup_exception(regs, X86_TRAP_GP))
	return;		return;

	tsk->thread.error_code = error_code;		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);		conditional_sti(regs);

	if (!user_mode(regs)) {		if (!user_mode(regs)) {
	if (!fixup_exception(regs)) {		if (!fixup_exception(regs, trapnr)) {
	task->thread.error_code = error_code;		task->thread.error_code = error_code;
	task->thread.trap_nr = trapnr;		task->thread.trap_nr = trapnr;
	die(str, regs, error_code);		die(str, regs, error_code);