only use exceptions for code in the .text section. Any other section
will cause the exception table to not be sorted correctly, and the
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.
/* Exception table entry */
#ifdef __ASSEMBLY__
-# define _ASM_EXTABLE(from,to) \
+# define _ASM_EXTABLE_HANDLE(from, to, handler) \
.pushsection "__ex_table","a" ; \
- .balign 8 ; \
+ .balign 4 ; \
.long (from) - . ; \
.long (to) - . ; \
+ .long (handler) - . ; \
.popsection
-# define _ASM_EXTABLE_EX(from,to) \
- .pushsection "__ex_table","a" ; \
- .balign 8 ; \
- .long (from) - . ; \
- .long (to) - . + 0x7ffffff0 ; \
- .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_NOKPROBE(entry) \
.pushsection "_kprobe_blacklist","aw" ; \
.endm
#else
-# define _ASM_EXTABLE(from,to) \
+# define _EXPAND_EXTABLE_HANDLE(x) #x
+# define _ASM_EXTABLE_HANDLE(from, to, handler) \
" .pushsection \"__ex_table\",\"a\"\n" \
- " .balign 8\n" \
+ " .balign 4\n" \
" .long (" #from ") - .\n" \
" .long (" #to ") - .\n" \
+ " .long (" _EXPAND_EXTABLE_HANDLE(handler) ") - .\n" \
" .popsection\n"
-# define _ASM_EXTABLE_EX(from,to) \
- " .pushsection \"__ex_table\",\"a\"\n" \
- " .balign 8\n" \
- " .long (" #from ") - .\n" \
- " .long (" #to ") - . + 0x7ffffff0\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)
+
/* For C file, we already have NOKPROBE_SYMBOL macro */
#endif
likely(!__range_not_ok(addr, size, user_addr_max()))
/*
- * 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.
+ * 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.
*
* 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,
*/
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 bool ex_has_fault_handler(unsigned long ip);
extern int early_fixup_exception(unsigned long *ip);
/*
* In case the user-specified fault handler returned
* zero, try to fix up.
*/
- if (fixup_exception(regs))
+ if (fixup_exception(regs, trapnr))
return 1;
/*
}
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);
tsk = current;
if (!user_mode(regs)) {
- if (fixup_exception(regs))
+ if (fixup_exception(regs, X86_TRAP_GP))
return;
tsk->thread.error_code = error_code;
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);
#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)
{
{
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);
+}
-int fixup_exception(struct pt_regs *regs)
+bool 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 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)
+{
+ const struct exception_table_entry *e;
+ ex_handler_t handler;
#ifdef CONFIG_PNPBIOS
if (unlikely(SEGMENT_IS_PNP_CODE(regs->cs))) {
}
#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;
- }
+ /* special handling not supported during early boot */
+ if (handler != ex_handler_default)
+ return 0;
- return 0;
+ *ip = new_ip;
+ return 1;
}
/*
i += 4;
p->fixup += i;
i += 4;
+ p->handler += i;
+ i += 4;
}
sort(start, finish - start, sizeof(struct exception_table_entry),
i += 4;
p->fixup -= i;
i += 4;
+ p->handler -= i;
+ i += 4;
}
}
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
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;
break;
case EM_386:
case EM_X86_64:
+ custom_sort = x86_sort_relative_table;
+ break;
+
case EM_S390:
custom_sort = sort_relative_table;
break;
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