Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751555AbbFLBoO (ORCPT ); Thu, 11 Jun 2015 21:44:14 -0400 Received: from ozlabs.org ([103.22.144.67]:36622 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750875AbbFLBoF (ORCPT ); Thu, 11 Jun 2015 21:44:05 -0400 From: Rusty Russell To: Dan Streetman Cc: Jani Nikula , Greg Kroah-Hartman , "David S. Miller" , Christoph Hellwig , Andrew Morton , linux-kernel , Dan Streetman Subject: Re: [PATCH] module: make perm const, change BUG_ON to BUILD_BUG_ON In-Reply-To: <1433958254-6776-1-git-send-email-ddstreet@ieee.org> References: <1433958254-6776-1-git-send-email-ddstreet@ieee.org> User-Agent: Notmuch/0.17 (http://notmuchmail.org) Emacs/24.4.1 (x86_64-pc-linux-gnu) Date: Fri, 12 Jun 2015 11:13:45 +0930 Message-ID: <87y4jpg0q6.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5831 Lines: 168 Dan Streetman 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 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 Signed-off-by: Rusty Russell (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++] = ','; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/