From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-24.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1,USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B9F33C433ED for ; Tue, 20 Apr 2021 14:42:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7AE0B6100A for ; Tue, 20 Apr 2021 14:42:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232277AbhDTOmm (ORCPT ); Tue, 20 Apr 2021 10:42:42 -0400 Received: from linux.microsoft.com ([13.77.154.182]:55562 "EHLO linux.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232174AbhDTOmm (ORCPT ); Tue, 20 Apr 2021 10:42:42 -0400 Received: from [192.168.0.104] (c-73-42-176-67.hsd1.wa.comcast.net [73.42.176.67]) by linux.microsoft.com (Postfix) with ESMTPSA id 9A08120B8001; Tue, 20 Apr 2021 07:42:10 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 9A08120B8001 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1618929730; bh=NVm2vo4GXXRMexKDwSwg3+CXMqPX9ItM3I9tjQFYJeI=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=hepldv/2ui8GWJoHLyLWTVwmm7kq5UZFZipOgtP3OsMPbMS9OYkxhqJnRuBEqq1pz bkxXeMEs2LfKkTxZ2eAUkbIvjhEm/6oJHz4TChxZn9vCS57zzDEv7MyH7h66bossYy NjuigEso0BBbnxccOgktltZzkcaxa9xPIai7Xxjc= Subject: Re: [PATCH] powerpc: Initialize local variable fdt to NULL in elf64_load() To: Rob Herring Cc: Dan Carpenter , Michael Ellerman , Daniel Axtens , devicetree@vger.kernel.org, linuxppc-dev , kbuild-all@lists.01.org, Thiago Jung Bauermann , kbuild test robot References: <20210415191437.20212-1-nramas@linux.microsoft.com> <4edb1433-4d1e-5719-ec9c-fd232b7cf71f@linux.microsoft.com> <87eefag241.fsf@linkitivity.dja.id.au> <87tuo6eh0j.fsf@mpe.ellerman.id.au> <2817d674-d420-580f-a0c1-b842da915a80@linux.microsoft.com> <87pmypdf93.fsf@mpe.ellerman.id.au> <20210420050015.GA1959@kadam> From: Lakshmi Ramasubramanian Message-ID: <2e8dd39b-0372-4874-340e-6f87185091cc@linux.microsoft.com> Date: Tue, 20 Apr 2021 07:42:10 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On 4/20/21 6:06 AM, Rob Herring wrote: > On Tue, Apr 20, 2021 at 12:20 AM Lakshmi Ramasubramanian > wrote: >> >> On 4/19/21 10:00 PM, Dan Carpenter wrote: >>> On Tue, Apr 20, 2021 at 09:30:16AM +1000, Michael Ellerman wrote: >>>> Lakshmi Ramasubramanian writes: >>>>> On 4/16/21 2:05 AM, Michael Ellerman wrote: >>>>> >>>>>> Daniel Axtens writes: >>>>>>>> On 4/15/21 12:14 PM, Lakshmi Ramasubramanian wrote: >>>>>>>> >>>>>>>> Sorry - missed copying device-tree and powerpc mailing lists. >>>>>>>> >>>>>>>>> There are a few "goto out;" statements before the local variable "fdt" >>>>>>>>> is initialized through the call to of_kexec_alloc_and_setup_fdt() in >>>>>>>>> elf64_load(). This will result in an uninitialized "fdt" being passed >>>>>>>>> to kvfree() in this function if there is an error before the call to >>>>>>>>> of_kexec_alloc_and_setup_fdt(). >>>>>>>>> >>>>>>>>> Initialize the local variable "fdt" to NULL. >>>>>>>>> >>>>>>> I'm a huge fan of initialising local variables! But I'm struggling to >>>>>>> find the code path that will lead to an uninit fdt being returned... >>>>>>> >>>>>>> The out label reads in part: >>>>>>> >>>>>>> /* Make kimage_file_post_load_cleanup free the fdt buffer for us. */ >>>>>>> return ret ? ERR_PTR(ret) : fdt; >>>>>>> >>>>>>> As far as I can tell, any time we get a non-zero ret, we're going to >>>>>>> return an error pointer rather than the uninitialised value... >>>>> >>>>> As Dan pointed out, the new code is in linux-next. >>>>> >>>>> I have copied the new one below - the function doesn't return fdt, but >>>>> instead sets it in the arch specific field (please see the link to the >>>>> updated elf_64.c below). >>>>> >>>>> https://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git/tree/arch/powerpc/kexec/elf_64.c?h=for-next >>>>> >>>>>>> >>>>>>> (btw, it does look like we might leak fdt if we have an error after we >>>>>>> successfully kmalloc it.) >>>>>>> >>>>>>> Am I missing something? Can you link to the report for the kernel test >>>>>>> robot or from Dan? >>>>> >>>>> /* >>>>> * Once FDT buffer has been successfully passed to >>>>> kexec_add_buffer(), >>>>> * the FDT buffer address is saved in image->arch.fdt. In that >>>>> case, >>>>> * the memory cannot be freed here in case of any other error. >>>>> */ >>>>> if (ret && !image->arch.fdt) >>>>> kvfree(fdt); >>>>> >>>>> return ret ? ERR_PTR(ret) : NULL; >>>>> >>>>> In case of an error, the memory allocated for fdt is freed unless it has >>>>> already been passed to kexec_add_buffer(). >>>> >>>> It feels like the root of the problem is that the kvfree of fdt is in >>>> the wrong place. It's only allocated later in the function, so the error >>>> path should reflect that. Something like the patch below. >>>> >>>> cheers >>>> >>>> >>>> diff --git a/arch/powerpc/kexec/elf_64.c b/arch/powerpc/kexec/elf_64.c >>>> index 5a569bb51349..02662e72c53d 100644 >>>> --- a/arch/powerpc/kexec/elf_64.c >>>> +++ b/arch/powerpc/kexec/elf_64.c >>>> @@ -114,7 +114,7 @@ static void *elf64_load(struct kimage *image, char *kernel_buf, >>>> ret = setup_new_fdt_ppc64(image, fdt, initrd_load_addr, >>>> initrd_len, cmdline); >>>> if (ret) >>>> - goto out; >>>> + goto out_free_fdt; >>>> >>>> fdt_pack(fdt); >>>> >>>> @@ -125,7 +125,7 @@ static void *elf64_load(struct kimage *image, char *kernel_buf, >>>> kbuf.mem = KEXEC_BUF_MEM_UNKNOWN; >>>> ret = kexec_add_buffer(&kbuf); >>>> if (ret) >>>> - goto out; >>>> + goto out_free_fdt; >>>> >>>> /* FDT will be freed in arch_kimage_file_post_load_cleanup */ >>>> image->arch.fdt = fdt; >>>> @@ -140,18 +140,14 @@ static void *elf64_load(struct kimage *image, char *kernel_buf, >>>> if (ret) >>>> pr_err("Error setting up the purgatory.\n"); >>>> >>>> + goto out; >>> >>> This will leak. It would need to be something like: >>> >>> if (ret) { >>> pr_err("Error setting up the purgatory.\n"); >>> goto out_free_fdt; >>> } >> Once "fdt" buffer is successfully passed to kexec_add_buffer() it cannot >> be freed here - it will be freed when the kexec cleanup function is called. > > That may be the case currently, but really if a function returns an > error it should have undone anything it did like memory allocations. I > don't think you should do that to fix this issue, but it would be a > good clean-up. > I agree - in case of an error the function should do a proper clean-up. Just to be clear - for now, I will leave this as is. Correct? In my patch, I will do the following changes: => Free "fdt" when possible (as Michael had suggested in his patch) => Zero out "elf_info" struct at the start of the function. thanks, -lakshmi