diff mbox

[v7,1/3] x86: Add classes to exception tables

Message ID 20160108014526.GA31242@agluck-desk.sc.intel.com (mailing list archive)
State New, archived
Headers show

Commit Message

Tony Luck Jan. 8, 2016, 1:45 a.m. UTC 
On Thu, Jan 07, 2016 at 01:11:31PM +0100, Borislav Petkov wrote:
> Anyway, here's what I have, it boots fine in a guest.
> 
> Btw, it seems I'm coming down with the cold and all that above could be
> hallucinations so please double-check me.

Hardly any hallucinations ... here's an update with the changes
I mentioned in earlier e-mail.  Boots on actual h/w.

Comments

Borislav Petkov Jan. 8, 2016, 10:37 a.m. UTC | #1 
On Thu, Jan 07, 2016 at 05:45:26PM -0800, Luck, Tony wrote:
> On Thu, Jan 07, 2016 at 01:11:31PM +0100, Borislav Petkov wrote:
> > Anyway, here's what I have, it boots fine in a guest.
> > 
> > Btw, it seems I'm coming down with the cold and all that above could be
> > hallucinations so please double-check me.
> 
> Hardly any hallucinations ... here's an update with the changes
> I mentioned in earlier e-mail.  Boots on actual h/w.

Cool, thanks for fixing it up. Looks good to me. Feel free to make it
into a proper patch and add it to your series... unless you want me to
do it.

Just one small question below:

> diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
> index 903ec1e9c326..01098ad010dd 100644
> --- a/arch/x86/mm/extable.c
> +++ b/arch/x86/mm/extable.c
> @@ -3,6 +3,8 @@
>  #include <linux/sort.h>
>  #include <asm/uaccess.h>
>  
> +typedef int (*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)
>  {
> @@ -14,10 +16,39 @@ ex_fixup_addr(const struct exception_table_entry *x)
>  	return (unsigned long)&x->fixup + x->fixup;
>  }
>  
> -int fixup_exception(struct pt_regs *regs)
> +int ex_handler_default(const struct exception_table_entry *fixup,
> +		       struct pt_regs *regs, int trapnr)
>  {
> -	const struct exception_table_entry *fixup;
> -	unsigned long new_ip;
> +	regs->ip = ex_fixup_addr(fixup);
> +	return 1;
> +}
> +EXPORT_SYMBOL(ex_handler_default);

Why not EXPORT_SYMBOL_GPL() ?

We do not care about external modules.
Tony Luck Jan. 8, 2016, 4:29 p.m. UTC | #2 
>> +EXPORT_SYMBOL(ex_handler_default);
>
> Why not EXPORT_SYMBOL_GPL() ?
>
> We do not care about external modules.

I thought the guideline was that new features are GPL, but changes
to existing features shouldn't break by adding new GPL requirements.

The point is moot though because  the shared hallucinations wore
off this morning and I realized that having the "handler" be a pointer
to a function can't work. We're storing the 32-bit signed offset from
the extable to the target address. This is fine if the table and the
address are close together. But for modules we have an exception
table wherever vmalloc() loaded the module, and a function back
in the base kernel.

So back to your ".long 0" for the default case.  And if we want to allow
modules to use any of the new handlers, then we can't use
relative function pointers for them either.

So I'm looking at making the new field just a simple integer and using
it to index an array of function pointers (like in v7).

Unless someone has a better idea?

-Tony
Borislav Petkov Jan. 8, 2016, 5:20 p.m. UTC | #3 
On Fri, Jan 08, 2016 at 04:29:49PM +0000, Luck, Tony wrote:
> I thought the guideline was that new features are GPL, but changes
> to existing features shouldn't break by adding new GPL requirements.
> 
> The point is moot though because  the shared hallucinations wore
> off this morning and I realized that having the "handler" be a pointer
> to a function can't work. We're storing the 32-bit signed offset from
> the extable to the target address. This is fine if the table and the
> address are close together. But for modules we have an exception
> table wherever vmalloc() loaded the module, and a function back
> in the base kernel.

Whoops, true story.

> So back to your ".long 0" for the default case.  And if we want to allow
> modules to use any of the new handlers, then we can't use
> relative function pointers for them either.
> 
> So I'm looking at making the new field just a simple integer and using
> it to index an array of function pointers (like in v7).

Right, that sounds good too. I guess we can even split the integer into

[0 ... 7][8 ... 31]

where slice [0:7] is an index into the handlers array and the remaining
unused 24-bits could be used for other stuff later. Normal addition as a
way to OR values should work.
Brian Gerst Jan. 8, 2016, 10:29 p.m. UTC | #4 
On Fri, Jan 8, 2016 at 11:29 AM, Luck, Tony <tony.luck@intel.com> wrote:
>>> +EXPORT_SYMBOL(ex_handler_default);
>>
>> Why not EXPORT_SYMBOL_GPL() ?
>>
>> We do not care about external modules.
>
> I thought the guideline was that new features are GPL, but changes
> to existing features shouldn't break by adding new GPL requirements.
>
> The point is moot though because  the shared hallucinations wore
> off this morning and I realized that having the "handler" be a pointer
> to a function can't work. We're storing the 32-bit signed offset from
> the extable to the target address. This is fine if the table and the
> address are close together. But for modules we have an exception
> table wherever vmalloc() loaded the module, and a function back
> in the base kernel.
>
> So back to your ".long 0" for the default case.  And if we want to allow
> modules to use any of the new handlers, then we can't use
> relative function pointers for them either.
>
> So I'm looking at making the new field just a simple integer and using
> it to index an array of function pointers (like in v7).
>
> Unless someone has a better idea?

Aren't modules loaded in the top 2GB of address space like the main
kernel?  Otherwise rip-relative addressing wouldn't work and modules
would have to be compiled as PIC.

--
Brian Gerst
diff mbox

Patch

diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 189679aba703..c286db8ddc58 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -46,16 +46,18 @@ 
 #ifdef __ASSEMBLY__
 # define _ASM_EXTABLE(from,to)					\
 	.pushsection "__ex_table","a" ;				\
-	.balign 8 ;						\
+	.balign 4 ;						\
 	.long (from) - . ;					\
 	.long (to) - . ;					\
+	.long ex_handler_default - . ;				\
 	.popsection
 
 # define _ASM_EXTABLE_EX(from,to)				\
 	.pushsection "__ex_table","a" ;				\
-	.balign 8 ;						\
+	.balign 4 ;						\
 	.long (from) - . ;					\
-	.long (to) - . + 0x7ffffff0 ;				\
+	.long (to) - . ;					\
+	.long ex_handler_ext - . ;				\
 	.popsection
 
 # define _ASM_NOKPROBE(entry)					\
@@ -91,16 +93,18 @@ 
 #else
 # define _ASM_EXTABLE(from,to)					\
 	" .pushsection \"__ex_table\",\"a\"\n"			\
-	" .balign 8\n"						\
+	" .balign 4\n"						\
 	" .long (" #from ") - .\n"				\
 	" .long (" #to ") - .\n"				\
+	" .long ex_handler_default - .\n"			\
 	" .popsection\n"
 
 # define _ASM_EXTABLE_EX(from,to)				\
 	" .pushsection \"__ex_table\",\"a\"\n"			\
-	" .balign 8\n"						\
+	" .balign 4\n"						\
 	" .long (" #from ") - .\n"				\
-	" .long (" #to ") - . + 0x7ffffff0\n"			\
+	" .long (" #to ") - .\n"				\
+	" .long ex_handler_ext - .\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 a8df874f3e88..b8f6f7545679 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -104,13 +104,13 @@  static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
  */
 
 struct exception_table_entry {
-	int insn, fixup;
+	int insn, fixup, handler;
 };
 /* 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);
+extern int fixup_exception(struct pt_regs *regs, int trapnr);
 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 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 346eec73f7db..7f50e8f4a075 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);
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 903ec1e9c326..01098ad010dd 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -3,6 +3,8 @@ 
 #include <linux/sort.h>
 #include <asm/uaccess.h>
 
+typedef int (*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)
 {
@@ -14,10 +16,39 @@  ex_fixup_addr(const struct exception_table_entry *x)
 	return (unsigned long)&x->fixup + x->fixup;
 }
 
-int fixup_exception(struct pt_regs *regs)
+int ex_handler_default(const struct exception_table_entry *fixup,
+		       struct pt_regs *regs, int trapnr)
 {
-	const struct exception_table_entry *fixup;
-	unsigned long new_ip;
+	regs->ip = ex_fixup_addr(fixup);
+	return 1;
+}
+EXPORT_SYMBOL(ex_handler_default);
+
+int 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 1;
+}
+int 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 1;
+}
+
+inline ex_handler_t ex_fixup_handler(const struct exception_table_entry *x)
+{
+	return (ex_handler_t)&x->handler + x->handler;
+}
+
+int fixup_exception(struct pt_regs *regs, int trapnr)
+{
+	const struct exception_table_entry *e;
+	ex_handler_t handler;
 
 #ifdef CONFIG_PNPBIOS
 	if (unlikely(SEGMENT_IS_PNP_CODE(regs->cs))) {
@@ -33,42 +64,35 @@  int fixup_exception(struct pt_regs *regs)
 	}
 #endif
 
-	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;
-	}
+	e = search_exception_tables(regs->ip);
+	if (!e)
+		return 0;
 
-	return 0;
+	handler = ex_fixup_handler(e);
+
+	return handler(e, regs, trapnr);
 }
 
 /* Restricted version used during very early boot */
 int __init early_fixup_exception(unsigned long *ip)
 {
-	const struct exception_table_entry *fixup;
+	const struct exception_table_entry *e;
 	unsigned long new_ip;
+	ex_handler_t handler;
 
-	fixup = search_exception_tables(*ip);
-	if (fixup) {
-		new_ip = ex_fixup_addr(fixup);
+	e = search_exception_tables(*ip);
+	if (!e)
+		return 0;
 
-		if (fixup->fixup - fixup->insn >= 0x7ffffff0 - 4) {
-			/* uaccess handling not supported during early boot */
-			return 0;
-		}
+	new_ip  = ex_fixup_addr(e);
+	handler = ex_fixup_handler(e);
 
-		*ip = new_ip;
-		return 1;
-	}
+	/* uaccess handling not supported during early boot */
+	if (handler == ex_handler_ext)
+		return 0;
 
-	return 0;
+	*ip = new_ip;
+	return 1;
 }
 
 /*
@@ -133,6 +157,8 @@  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),
@@ -145,6 +171,8 @@  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 eef44d9a3f77..495946c3f9dd 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -656,7 +656,7 @@  no_context(struct pt_regs *regs, unsigned long error_code,
 	int sig;
 
 	/* Are we prepared to handle this kernel fault? */
-	if (fixup_exception(regs)) {
+	if (fixup_exception(regs, X86_TRAP_PF)) {
 		/*
 		 * Any interrupt that takes a fault gets the fixup. This makes
 		 * the below recursive fault logic only apply to a faults from
diff --git a/scripts/sortextable.c b/scripts/sortextable.c
index c2423d913b46..7b29fb14f870 100644
--- a/scripts/sortextable.c
+++ b/scripts/sortextable.c
@@ -209,6 +209,35 @@  static int compare_relative_table(const void *a, const void *b)
 	return 0;
 }
 
+static void x86_sort_relative_table(char *extab_image, int image_size)
+{
+	int i;
+
+	i = 0;
+	while (i < image_size) {
+		uint32_t *loc = (uint32_t *)(extab_image + i);
+
+		w(r(loc) + i, loc);
+		w(r(loc + 1) + i + 4, loc + 1);
+		w(r(loc + 2) + i + 8, loc + 2);
+
+		i += sizeof(uint32_t) * 3;
+	}
+
+	qsort(extab_image, image_size / 12, 12, compare_relative_table);
+
+	i = 0;
+	while (i < image_size) {
+		uint32_t *loc = (uint32_t *)(extab_image + i);
+
+		w(r(loc) - i, loc);
+		w(r(loc + 1) - (i + 4), loc + 1);
+		w(r(loc + 2) - (i + 8), loc + 2);
+
+		i += sizeof(uint32_t) * 3;
+	}
+}
+
 static void sort_relative_table(char *extab_image, int image_size)
 {
 	int i;
@@ -281,6 +310,9 @@  do_file(char const *const fname)
 		break;
 	case EM_386:
 	case EM_X86_64:
+		custom_sort = x86_sort_relative_table;
+		break;
+
 	case EM_S390:
 		custom_sort = sort_relative_table;
 		break;