From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752436AbbKKRna (ORCPT ); Wed, 11 Nov 2015 12:43:30 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48249 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750942AbbKKRn2 (ORCPT ); Wed, 11 Nov 2015 12:43:28 -0500 Date: Wed, 11 Nov 2015 11:43:27 -0600 From: Josh Poimboeuf To: Chris J Arges Cc: live-patching@vger.kernel.org, jeyu@redhat.com, Seth Jennings , Jiri Kosina , Vojtech Pavlik , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3 v4] livepatch: add old_sympos as disambiguator field to klp_func Message-ID: <20151111174327.GE5331@treble.redhat.com> References: <20151103200608.GQ27488@treble.redhat.com> <1447259366-7055-1-git-send-email-chris.j.arges@canonical.com> <1447259366-7055-2-git-send-email-chris.j.arges@canonical.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1447259366-7055-2-git-send-email-chris.j.arges@canonical.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 11, 2015 at 10:28:59AM -0600, Chris J Arges wrote: > In cases of duplicate symbols, old_sympos will be used to disambiguate > instead of old_addr. By default old_sympos will be 0, and patching will > only succeed if the symbol is unique. Specifying a positive value will > ensure that occurrence of the symbol will be used for patching if it is > valid. Finally, old_addr is now an internal structure element and not to > be specified by the user. > > Signed-off-by: Chris J Arges > --- > include/linux/livepatch.h | 20 ++++++++++-------- > kernel/livepatch/core.c | 53 +++++++++++++++++++++++------------------------ > 2 files changed, 37 insertions(+), 36 deletions(-) > > diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h > index 31db7a0..df7b752 100644 > --- a/include/linux/livepatch.h > +++ b/include/linux/livepatch.h > @@ -37,8 +37,9 @@ enum klp_state { > * struct klp_func - function structure for live patching > * @old_name: name of the function to be patched > * @new_func: pointer to the patched function code > - * @old_addr: a hint conveying at what address the old function > - * can be found (optional, vmlinux patches only) > + * @old_sympos: a hint indicating which symbol position the old function > + * can be found (optional) > + * @old_addr: the address of the function being patched > * @kobj: kobject for sysfs resources > * @state: tracks function-level patch application state > * @stack_node: list node for klp_ops func_stack list > @@ -47,17 +48,18 @@ struct klp_func { > /* external */ > const char *old_name; > void *new_func; > + > /* > - * The old_addr field is optional and can be used to resolve > - * duplicate symbol names in the vmlinux object. If this > - * information is not present, the symbol is located by name > - * with kallsyms. If the name is not unique and old_addr is > - * not provided, the patch application fails as there is no > - * way to resolve the ambiguity. > + * The old_sympos field is optional and can be used to resolve > + * duplicate symbol names in livepatch objects. If this field is zero, > + * it is expected the symbol is unique, otherwise patching fails. If > + * this value is greater than zero then that occurrence of the symbol > + * in kallsyms is used. I would clarify this: ...occurrence of the symbol in kallsyms *for the given object* is used. > */ > - unsigned long old_addr; > + unsigned long old_sympos; > > /* internal */ > + unsigned long old_addr; > struct kobject kobj; > enum klp_state state; > struct list_head stack_node; > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c > index 6e53441..26f9778 100644 > --- a/kernel/livepatch/core.c > +++ b/kernel/livepatch/core.c > @@ -142,6 +142,7 @@ struct klp_find_arg { > * name in the same object. > */ > unsigned long count; > + unsigned long pos; There's a comment above this that says: /* * If count == 0, the symbol was not found. If count == 1, a unique * match was found and addr is set. If count > 1, there is * unresolvable ambiguity among "count" number of symbols with the same * name in the same object. */ That comment is no longer accurate and can probably be removed since IMO the purpose of 'count' is obvious. > }; > > static int klp_find_callback(void *data, const char *name, > @@ -159,36 +160,45 @@ static int klp_find_callback(void *data, const char *name, > return 0; > > /* > - * args->addr might be overwritten if another match is found > - * but klp_find_object_symbol() handles this and only returns the > - * addr if count == 1. > + * increment and assign address, return only if checking pos and > + * it matches count. > */ > - args->addr = addr; > args->count++; > + args->addr = addr; > + if ((args->pos > 0) && (args->count == args->pos)) > + return 1; > > return 0; > } > > static int klp_find_object_symbol(const char *objname, const char *name, > - unsigned long *addr) > + unsigned long *addr, unsigned long sympos) > { > struct klp_find_arg args = { > .objname = objname, > .name = name, > .addr = 0, > - .count = 0 > + .count = 0, > + .pos = sympos, > }; > > mutex_lock(&module_mutex); > kallsyms_on_each_symbol(klp_find_callback, &args); > mutex_unlock(&module_mutex); > > - if (args.count == 0) > + /* > + * Ensure an address was found. If sympos is 0, ensure symbol is unique; > + * otherwise ensure the symbol position count matches sympos. > + */ > + if (args.addr == 0) > pr_err("symbol '%s' not found in symbol table\n", name); > - else if (args.count > 1) > + else if (args.count > 1 && sympos == 0) { > pr_err("unresolvable ambiguity (%lu matches) on symbol '%s' in object '%s'\n", > args.count, name, objname); > - else { > + } else if (sympos != args.count && sympos > 0) { > + pr_err("symbol position %lu for symbol '%s' in object '%s' not found\n", > + sympos, name, objname ? objname : "vmlinux"); > + } else { > *addr = args.addr; > return 0; > } > @@ -239,22 +249,11 @@ static int klp_verify_vmlinux_symbol(const char *name, unsigned long addr) > static int klp_find_verify_func_addr(struct klp_object *obj, > struct klp_func *func) > { > - int ret; > - > -#if defined(CONFIG_RANDOMIZE_BASE) > - /* If KASLR has been enabled, adjust old_addr accordingly */ > - if (kaslr_enabled() && func->old_addr) > - func->old_addr += kaslr_offset(); > -#endif > - > - if (!func->old_addr || klp_is_module(obj)) > - ret = klp_find_object_symbol(obj->name, func->old_name, > - &func->old_addr); > - else > - ret = klp_verify_vmlinux_symbol(func->old_name, > - func->old_addr); > - > - return ret; > + /* > + * Verify the symbol, find old_addr, and write it to the structure. > + */ > + return klp_find_object_symbol(obj->name, func->old_name, > + &func->old_addr, func->old_sympos); klp_find_verify_func_addr() is no longer correctly named and can probably be removed since klp_init_object_loaded() can call klp_find_object_symbol() directly. > } > > /* > @@ -277,7 +276,7 @@ static int klp_find_external_symbol(struct module *pmod, const char *name, > preempt_enable(); > > /* otherwise check if it's in another .o within the patch module */ > - return klp_find_object_symbol(pmod->name, name, addr); > + return klp_find_object_symbol(pmod->name, name, addr, 0); > } > > static int klp_write_object_relocations(struct module *pmod, > @@ -307,7 +306,7 @@ static int klp_write_object_relocations(struct module *pmod, > else > ret = klp_find_object_symbol(obj->mod->name, > reloc->name, > - &reloc->val); > + &reloc->val, 0); > if (ret) > return ret; > } > -- > 1.9.1 > -- Josh