From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751315AbeCIDOh (ORCPT ); Thu, 8 Mar 2018 22:14:37 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:45322 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751078AbeCIDOc (ORCPT ); Thu, 8 Mar 2018 22:14:32 -0500 Date: Fri, 9 Mar 2018 11:14:20 +0800 From: Dave Young To: Philipp Rudo 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 Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180226151620.20970-10-prudo@linux.vnet.ibm.com> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.. > - * > - * 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