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Fri, 24 Apr 2020 02:35:24 +0000 (UTC) Received: from redhat.com (ovpn-112-171.phx2.redhat.com [10.3.112.171]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 31497600E8; Fri, 24 Apr 2020 02:35:23 +0000 (UTC) Date: Thu, 23 Apr 2020 22:35:21 -0400 From: Joe Lawrence To: Josh Poimboeuf Cc: Miroslav Benes , Gerald Schaefer , live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , Jessica Yu , linux-s390@vger.kernel.org, heiko.carstens@de.ibm.com, Vasily Gorbik Subject: Re: [PATCH v2 6/9] s390/module: Use s390_kernel_write() for late relocations Message-ID: <20200424023521.GA22117@redhat.com> References: <18266eb2c2c9a2ce0033426837d89dcb363a85d3.1587131959.git.jpoimboe@redhat.com> <20200422164037.7edd21ea@thinkpad> <20200422172126.743908f5@thinkpad> <20200422194605.n77t2wtx5fomxpyd@treble> <20200423141834.234ed0bc@thinkpad> <20200423141228.sjvnxwdqlzoyqdwg@treble> <20200423181030.b5mircvgc7zmqacr@treble> <20200423232657.7minzcsysnhp474w@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200423232657.7minzcsysnhp474w@treble> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Sender: live-patching-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: live-patching@vger.kernel.org On Thu, Apr 23, 2020 at 06:26:57PM -0500, Josh Poimboeuf wrote: > On Thu, Apr 23, 2020 at 01:10:30PM -0500, Josh Poimboeuf wrote: > > Mystery solved: > > > > $ CROSS_COMPILE=s390x-linux-gnu- scripts/faddr2line vmlinux apply_rela+0x16a/0x520 > > apply_rela+0x16a/0x520: > > apply_rela at arch/s390/kernel/module.c:336 > > > > which corresponds to the following code in apply_rela(): > > > > > > case R_390_PLTOFF64: /* 16 bit offset from GOT to PLT. */ > > if (info->plt_initialized == 0) { > > unsigned int *ip; > > ip = me->core_layout.base + me->arch.plt_offset + > > info->plt_offset; > > ip[0] = 0x0d10e310; /* basr 1,0 */ > > ip[1] = 0x100a0004; /* lg 1,10(1) */ > > > > > > Notice how it's writing directly to text... oops. > > Here's a fix, using write() for the PLT and the GOT. > > diff --git a/arch/s390/kernel/module.c b/arch/s390/kernel/module.c > index 2798329ebb74..fe446f42818f 100644 > --- a/arch/s390/kernel/module.c > +++ b/arch/s390/kernel/module.c > @@ -297,7 +297,7 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab, > > gotent = me->core_layout.base + me->arch.got_offset + > info->got_offset; > - *gotent = val; > + write(gotent, &val, sizeof(*gotent)); > info->got_initialized = 1; > } > val = info->got_offset + rela->r_addend; > @@ -330,25 +330,29 @@ static int apply_rela(Elf_Rela *rela, Elf_Addr base, Elf_Sym *symtab, > case R_390_PLTOFF32: /* 32 bit offset from GOT to PLT. */ > case R_390_PLTOFF64: /* 16 bit offset from GOT to PLT. */ > if (info->plt_initialized == 0) { > - unsigned int *ip; > + unsigned int *ip, insn[5]; > + > ip = me->core_layout.base + me->arch.plt_offset + > info->plt_offset; Would it be too paranoid to declare: const unsigned int *ip = me->core_layout.base + me->arch.plt_offset + info->plt_offset; That would trip an assignment to read-only error if someone were tempted to write directly through the pointer in the future. Ditto for Elf_Addr *gotent pointer in the R_390_GOTPLTENT case. -- Joe