From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751005AbeCIKCw (ORCPT ); Fri, 9 Mar 2018 05:02:52 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:52860 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750800AbeCIKCu (ORCPT ); Fri, 9 Mar 2018 05:02:50 -0500 Date: Fri, 9 Mar 2018 11:02:41 +0100 From: Philipp Rudo To: Dave Young Cc: kexec@lists.infradead.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, Eric Biederman , Vivek Goyal , Michael Ellerman , Thiago Jung Bauermann , Martin Schwidefsky , Heiko Carstens , Andrew Morton , x86@kernel.org, AKASHI Takahiro Subject: Re: [PATCH 09/11] kexec_file: Remove mis-use of sh_offset field In-Reply-To: <20180309031420.GA3246@dhcp-128-65.nay.redhat.com> References: <20180226151620.20970-1-prudo@linux.vnet.ibm.com> <20180226151620.20970-10-prudo@linux.vnet.ibm.com> <20180309031420.GA3246@dhcp-128-65.nay.redhat.com> Organization: IBM X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 18030910-0008-0000-0000-000004D9C471 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18030910-0009-0000-0000-00001E6CE7F3 Message-Id: <20180309110241.00b0d3f3@ThinkPad> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-03-09_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1803090129 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Dave, On Fri, 9 Mar 2018 11:14:20 +0800 Dave Young wrote: > On 02/26/18 at 04:16pm, Philipp Rudo wrote: > > The current code uses the sh_offset field in purgatory_info->sechdrs to > > store a pointer to the current load address of the section. Depending > > whether the section will be loaded or not this is either a pointer into > > purgatory_info->purgatory_buf or kexec_purgatory. This is not only a > > violation of the ELF standard but also makes the code very hard to > > understand as you cannot tell if the memory you are using is read-only or > > not. > > > > Remove this mis-use and store the offset of the section in > > pugaroty_info->purgatory_buf in sh_offset. > > > > Signed-off-by: Philipp Rudo > > --- > > arch/x86/kernel/machine_kexec_64.c | 10 ++++++---- > > kernel/kexec_file.c | 33 +++------------------------------ > > 2 files changed, 9 insertions(+), 34 deletions(-) > > > > diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c > > index 51667c8b5c9b..41db74bdc88b 100644 > > --- a/arch/x86/kernel/machine_kexec_64.c > > +++ b/arch/x86/kernel/machine_kexec_64.c > > @@ -457,13 +457,15 @@ int arch_kexec_apply_relocations_add(struct purgatory_info *pi, > > * rel[i].r_offset contains byte offset from beginning > > * of section to the storage unit affected. > > * > > - * This is location to update (->sh_offset). This is temporary > > - * buffer where section is currently loaded. This will finally > > - * be loaded to a different address later, pointed to by > > + * This is location to update. This is temporary buffer > > + * where section is currently loaded. This will finally be > > + * loaded to a different address later, pointed to by > > * ->sh_addr. kexec takes care of moving it > > * (kexec_load_segment()). > > */ > > - location = (void *)(section->sh_offset + rel[i].r_offset); > > + location = pi->purgatory_buf; > > + location += section->sh_offset; > > + location += rel[i].r_offset; > > > > /* Final address of the location */ > > address = section->sh_addr + rel[i].r_offset; > > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c > > index 746b91e46e34..25b44d1a664a 100644 > > --- a/kernel/kexec_file.c > > +++ b/kernel/kexec_file.c > > @@ -736,28 +736,6 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi, > > pi->ehdr->e_shnum * sizeof(Elf_Shdr)); > > pi->sechdrs = sechdrs; > > > > - /* > > - * We seem to have multiple copies of sections. First copy is which > > - * is embedded in kernel in read only section. Some of these sections > > - * will be copied to a temporary buffer and relocated. And these > > - * sections will finally be copied to their final destination at > > - * segment load time. > > It would be good to keep above part comment somewhere.. there is a comment in include/linux/kexec.h for the purgatory_info->sechdrs field saying Temporary, modifiable buffer for sechdrs used for relocation. This memory can be freed post image load When you think this is not enough i can add a comment here like The section headers in kexec_purgatory are read-only. In order to have them modifiable make a temporary copy. What do you think. Thanks Philipp > > - * > > - * Use ->sh_offset to reflect section address in memory. It will > > - * point to original read only copy if section is not allocatable. > > - * Otherwise it will point to temporary copy which will be relocated. > > - * > > - * Use ->sh_addr to contain final address of the section where it > > - * will go during execution time. > > - */ > > - for (i = 0; i < pi->ehdr->e_shnum; i++) { > > - if (sechdrs[i].sh_type == SHT_NOBITS) > > - continue; > > - > > - sechdrs[i].sh_offset = (unsigned long)pi->ehdr + > > - sechdrs[i].sh_offset; > > - } > > - > > offset = 0; > > bss_addr = kbuf->mem + kbuf->bufsz; > > kbuf->image->start = pi->ehdr->e_entry; > > @@ -786,17 +764,12 @@ static int kexec_purgatory_setup_sechdrs(struct purgatory_info *pi, > > kbuf->image->start += kbuf->mem + offset; > > } > > > > - src = (void *)sechdrs[i].sh_offset; > > + src = (void *)pi->ehdr + sechdrs[i].sh_offset; > > dst = pi->purgatory_buf + offset; > > memcpy(dst, src, sechdrs[i].sh_size); > > > > sechdrs[i].sh_addr = kbuf->mem + offset; > > - > > - /* > > - * This section got copied to temporary buffer. Update > > - * ->sh_offset accordingly. > > - */ > > - sechdrs[i].sh_offset = (unsigned long)dst; > > + sechdrs[i].sh_offset = offset; > > offset += sechdrs[i].sh_size; > > } > > > > @@ -1006,7 +979,7 @@ int kexec_purgatory_get_set_symbol(struct kimage *image, const char *name, > > return -EINVAL; > > } > > > > - sym_buf = (char *)sec->sh_offset + sym->st_value; > > + sym_buf = (char *)pi->purgatory_buf + sec->sh_offset + sym->st_value; > > > > if (get_value) > > memcpy((void *)buf, sym_buf, size); > > -- > > 2.13.5 > > > > Thanks > Dave >