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Date: Wed, 6 Jan 2016 13:33:46 +0100
From: Borislav Petkov <bp@...en8.de>
To: Tony Luck <tony.luck@...el.com>
Cc: Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Andy Lutomirski <luto@...nel.org>,
Dan Williams <dan.j.williams@...el.com>, elliott@....com,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
linux-nvdimm@...1.01.org, x86@...nel.org
Subject: Re: [PATCH v7 1/3] x86: Add classes to exception tables
On Wed, Dec 30, 2015 at 09:59:29AM -0800, Tony Luck wrote:
> Starting with a patch from Andy Lutomirski <luto@...capital.net>
> that used linker relocation trickery to free up a couple of bits
> in the "fixup" field of the exception table (and generalized the
> uaccess_err hack to use one of the classes).
So I still think that the other idea Andy gave with putting the handler
in the exception table is much cleaner and straightforward.
Here's a totally untested patch which at least builds here. I think this
approach is much more extensible and simpler for the price of a couple
of KBs of __ex_table size.
---
diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 189679aba703..43b509c88b13 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -44,18 +44,20 @@
/* Exception table entry */
#ifdef __ASSEMBLY__
-# define _ASM_EXTABLE(from,to) \
+# define _ASM_EXTABLE(from,to) \
.pushsection "__ex_table","a" ; \
.balign 8 ; \
.long (from) - . ; \
.long (to) - . ; \
+ .long 0 - .; \
.popsection
# define _ASM_EXTABLE_EX(from,to) \
.pushsection "__ex_table","a" ; \
.balign 8 ; \
.long (from) - . ; \
- .long (to) - . + 0x7ffffff0 ; \
+ .long (to) - . ; \
+ .long ex_handler_ext - . ; \
.popsection
# define _ASM_NOKPROBE(entry) \
@@ -94,13 +96,14 @@
" .balign 8\n" \
" .long (" #from ") - .\n" \
" .long (" #to ") - .\n" \
+ " .long 0 - .\n" \
" .popsection\n"
# define _ASM_EXTABLE_EX(from,to) \
" .pushsection \"__ex_table\",\"a\"\n" \
" .balign 8\n" \
" .long (" #from ") - .\n" \
- " .long (" #to ") - . + 0x7ffffff0\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 09b1b0ab94b7..22b49c3b311a 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 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);
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 903ec1e9c326..191f4b7d1d2d 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)
+inline ex_handler_t ex_fixup_handler(const struct exception_table_entry *x)
+{
+ return (ex_handler_t)&x->handler + x->handler;
+}
+
+int ex_handler_default(const struct exception_table_entry *fixup,
+ struct pt_regs *regs, int trapnr)
+{
+ regs->ip = ex_fixup_addr(fixup);
+ return 1;
+}
+
+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)
{
- const struct exception_table_entry *fixup;
+ /* Special hack for uaccess_err */
+ current_thread_info()->uaccess_err = 1;
+ regs->ip = ex_fixup_addr(fixup);
+ return 1;
+}
+
+int fixup_exception(struct pt_regs *regs, int trapnr)
+{
+ const struct exception_table_entry *e;
unsigned long new_ip;
+ ex_handler_t handler;
#ifdef CONFIG_PNPBIOS
if (unlikely(SEGMENT_IS_PNP_CODE(regs->cs))) {
@@ -33,42 +64,40 @@ 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;
+
+ new_ip = ex_fixup_addr(e);
+ handler = ex_fixup_handler(e);
+
+ if (!handler)
+ handler = ex_handler_default;
+
+ 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 *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 && handler == ex_handler_ext)
+ return 0;
- return 0;
+ *ip = new_ip;
+ return 1;
}
/*
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
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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