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Date: Fri, 12 Jun 2015 11:13:45 +0930
From: Rusty Russell <rusty@...tcorp.com.au>
To: Dan Streetman <ddstreet@...e.org>
Cc: Jani Nikula <jani.nikula@...el.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"David S. Miller" <davem@...emloft.net>,
Christoph Hellwig <hch@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Dan Streetman <ddstreet@...e.org>
Subject: Re: [PATCH] module: make perm const, change BUG_ON to BUILD_BUG_ON
Dan Streetman <ddstreet@...e.org> writes:
> Change the struct kernel_param.perm field to a const, as it should never
> be changed. Add inline functions that return a const value, which are
> compiled out, for kparam_[un]block_sysfs_r/w() macros to use; and change
> the BUG_ON() in those macros to BUILD_BUG_ON().
Nice win!
I think it's slightly clearer if we just declare:
static __always_unused const u16 __param_perm_##name = (perm).
And indeed, gcc (at least 4.9) eliminates it correctly.
So, here's your patch with that mod, and the param.c noise removed.
It's in my pending queue for the moment.
I still am leaning towards just removing these wrappers and exposing
the (new) per-module mutex though. Happy for that patch to replace this
one, if you send it.
Thanks,
Rusty.
From: Dan Streetman <ddstreet@...e.org>
Subject: module: make perm const, change BUG_ON to BUILD_BUG_ON
Change the struct kernel_param.perm field to a const, as it should never
be changed. Add a static const name for this (which gcc compiles out)
for kparam_[un]block_sysfs_r/w() macros to use; and change the BUG_ON()
in those macros to BUILD_BUG_ON().
This will enforce that the kernel_param permissions are never changed,
and it will fail at build instead of runtime for any misuse of
sysfs param blocking.
I initially wanted to just use the const param.perm in the block_sysfs
checks, but unfortunately that also requires the param itself to be
const, in order to do const folding into a constant compiletime
condition to BUILD_BUG_ON(), and on some archs the params aren't defined
as const:
/* On alpha, ia64 and ppc64 relocations to global data cannot go into
read-only sections (which is part of respective UNIX ABI on these
platforms). So 'const' makes no sense and even causes compile failures
with some compilers. */
Signed-off-by: Dan Streetman <ddstreet@...e.org>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au> (slight tweak)
diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
index 7e0079936396..347e11f3bc32 100644
--- a/include/linux/moduleparam.h
+++ b/include/linux/moduleparam.h
@@ -68,7 +68,7 @@ enum {
struct kernel_param {
const char *name;
const struct kernel_param_ops *ops;
- u16 perm;
+ const u16 perm;
s8 level;
u8 flags;
union {
@@ -215,8 +215,10 @@ struct kparam_array
/* This is the fundamental function for registering boot/module
parameters. */
#define __module_param_call(prefix, name, ops, arg, perm, level, flags) \
+ /* These allow kparam_block_sysfs_*() to use BUILD_BUG_ON() */ \
+ static __always_unused const u16 __param_perm_##name = (perm); \
/* Default value instead of permissions? */ \
- static const char __param_str_##name[] = prefix #name; \
+ static const char __param_str_##name[] = prefix #name; \
static struct kernel_param __moduleparam_const __param_##name \
__used \
__attribute__ ((unused,__section__ ("__param"),aligned(sizeof(void *)))) \
@@ -244,20 +246,20 @@ __check_old_set_param(int (*oldset)(const char *, struct kernel_param *))
*
* There's no point blocking write on a paramter that isn't writable via sysfs!
*/
-#define kparam_block_sysfs_write(name) \
- do { \
- BUG_ON(!(__param_##name.perm & 0222)); \
- __kernel_param_lock(); \
+#define kparam_block_sysfs_write(name) \
+ do { \
+ BUILD_BUG_ON(!(__param_perm_##name & 0222)); \
+ __kernel_param_lock(); \
} while (0)
/**
* kparam_unblock_sysfs_write - allows sysfs to write to a parameter again.
* @name: the name of the parameter
*/
-#define kparam_unblock_sysfs_write(name) \
- do { \
- BUG_ON(!(__param_##name.perm & 0222)); \
- __kernel_param_unlock(); \
+#define kparam_unblock_sysfs_write(name) \
+ do { \
+ BUILD_BUG_ON(!(__param_perm_##name & 0222)); \
+ __kernel_param_unlock(); \
} while (0)
/**
@@ -266,20 +268,20 @@ __check_old_set_param(int (*oldset)(const char *, struct kernel_param *))
*
* This also blocks sysfs writes.
*/
-#define kparam_block_sysfs_read(name) \
- do { \
- BUG_ON(!(__param_##name.perm & 0444)); \
- __kernel_param_lock(); \
+#define kparam_block_sysfs_read(name) \
+ do { \
+ BUILD_BUG_ON(!(__param_perm_##name & 0444)); \
+ __kernel_param_lock(); \
} while (0)
/**
* kparam_unblock_sysfs_read - allows sysfs to read a parameter again.
* @name: the name of the parameter
*/
-#define kparam_unblock_sysfs_read(name) \
- do { \
- BUG_ON(!(__param_##name.perm & 0444)); \
- __kernel_param_unlock(); \
+#define kparam_unblock_sysfs_read(name) \
+ do { \
+ BUILD_BUG_ON(!(__param_perm_##name & 0444)); \
+ __kernel_param_unlock(); \
} while (0)
#ifdef CONFIG_SYSFS
diff --git a/kernel/params.c b/kernel/params.c
index 0b9bbdf830cb..15715a3efb50 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -395,12 +395,11 @@ EXPORT_SYMBOL(param_ops_invbool);
int param_set_bint(const char *val, const struct kernel_param *kp)
{
- struct kernel_param boolkp;
+ /* Match bool exactly, by re-using it. */
+ struct kernel_param boolkp = *kp;
bool v;
int ret;
- /* Match bool exactly, by re-using it. */
- boolkp = *kp;
boolkp.arg = &v;
ret = param_set_bool(val, &boolkp);
@@ -480,9 +479,8 @@ static int param_array_get(char *buffer, const struct kernel_param *kp)
{
int i, off, ret;
const struct kparam_array *arr = kp->arr;
- struct kernel_param p;
+ struct kernel_param p = *kp;
- p = *kp;
for (i = off = 0; i < (arr->num ? *arr->num : arr->max); i++) {
if (i)
buffer[off++] = ',';
--
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