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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BABA5C433EF for ; Thu, 30 Jun 2022 08:06:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233416AbiF3IGi (ORCPT ); Thu, 30 Jun 2022 04:06:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60736 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233567AbiF3IGh (ORCPT ); Thu, 30 Jun 2022 04:06:37 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C891441308; Thu, 30 Jun 2022 01:06:34 -0700 (PDT) Received: from dggpeml500023.china.huawei.com (unknown [172.30.72.55]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4LYW6G0jM8zTgGS; Thu, 30 Jun 2022 16:03:02 +0800 (CST) Received: from [10.67.110.112] (10.67.110.112) by dggpeml500023.china.huawei.com (7.185.36.114) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 30 Jun 2022 16:06:31 +0800 Subject: Re: [PATCH -next, v2] powerpc: add support for syscall stack randomization To: Christophe Leroy , "mpe@ellerman.id.au" , "benh@kernel.crashing.org" , "paulus@samba.org" , "npiggin@gmail.com" , "tglx@linutronix.de" , "mark.rutland@arm.com" CC: "linuxppc-dev@lists.ozlabs.org" , "linux-kernel@vger.kernel.org" , "linux-hardening@vger.kernel.org" References: <20220516073225.112875-1-xiujianfeng@huawei.com> From: xiujianfeng Message-ID: <50a540b6-1d36-c5f3-a01f-4da2706ec913@huawei.com> Date: Thu, 30 Jun 2022 16:06:31 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.110.112] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpeml500023.china.huawei.com (7.185.36.114) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org Hi, 在 2022/6/29 1:36, Christophe Leroy 写道: > > Le 16/05/2022 à 09:32, Xiu Jianfeng a écrit : >> Add support for adding a random offset to the stack while handling >> syscalls. This patch uses mftb() instead of get_random_int() for better >> performance. >> >> In order to avoid unconditional stack canaries on syscall entry (due to >> the use of alloca()), also disable stack protector to avoid triggering >> needless checks and slowing down the entry path. As there is no general >> way to control stack protector coverage with a function attribute, this >> must be disabled at the compilation unit level. >> >> Signed-off-by: Xiu Jianfeng >> > Did you see this patch generates sparse warnings ? > > See > https://patchwork.ozlabs.org/project/linuxppc-dev/patch/20220516073225.112875-1-xiujianfeng@huawei.com/ > > It is not directly related to this patch but that's worth a patch to fix it. Thanks for your reminder, the fix patch is here: https://lore.kernel.org/all/20220629060423.2515693-1-gongruiqi1@huawei.com/ >> --- >> Changes in v2: >> -move choose choose_random_kstack_offset() to the end of system_call_exception >> -allow full 6 (10) bits of entropy >> -disable stack-protector for interrupt.c >> --- >> arch/powerpc/Kconfig | 1 + >> arch/powerpc/kernel/Makefile | 7 +++++++ >> arch/powerpc/kernel/interrupt.c | 19 ++++++++++++++++++- >> 3 files changed, 26 insertions(+), 1 deletion(-) >> >> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig >> index 98309eeae09c..2f0019a0054e 100644 >> --- a/arch/powerpc/Kconfig >> +++ b/arch/powerpc/Kconfig >> @@ -192,6 +192,7 @@ config PPC >> select HAVE_ARCH_KASAN if PPC32 && PPC_PAGE_SHIFT <= 14 >> select HAVE_ARCH_KASAN_VMALLOC if PPC32 && PPC_PAGE_SHIFT <= 14 >> select HAVE_ARCH_KFENCE if PPC_BOOK3S_32 || PPC_8xx || 40x >> + select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET >> select HAVE_ARCH_KGDB >> select HAVE_ARCH_MMAP_RND_BITS >> select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT >> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile >> index 4ddd161aef32..5c5e85b8229b 100644 >> --- a/arch/powerpc/kernel/Makefile >> +++ b/arch/powerpc/kernel/Makefile >> @@ -40,6 +40,13 @@ CFLAGS_cputable.o += -DDISABLE_BRANCH_PROFILING >> CFLAGS_btext.o += -DDISABLE_BRANCH_PROFILING >> endif >> >> +#ifdef CONFIG_RANDOMIZE_KSTACK_OFFSET >> +# Remove stack protector to avoid triggering unneeded stack canary >> +# checks due to randomize_kstack_offset. >> +CFLAGS_REMOVE_interrupt.o = -fstack-protector -fstack-protector-strong >> +CFLAGS_interrupt.o += -fno-stack-protector >> +#endif >> + >> obj-y := cputable.o syscalls.o \ >> irq.o align.o signal_$(BITS).o pmc.o vdso.o \ >> process.o systbl.o idle.o \ >> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c >> index 784ea3289c84..d7cdcb6fc336 100644 >> --- a/arch/powerpc/kernel/interrupt.c >> +++ b/arch/powerpc/kernel/interrupt.c >> @@ -4,6 +4,7 @@ >> #include >> #include >> #include /* for show_regs */ >> +#include >> >> #include >> #include >> @@ -78,10 +79,12 @@ notrace long system_call_exception(long r3, long r4, long r5, >> long r6, long r7, long r8, >> unsigned long r0, struct pt_regs *regs) >> { >> + long ret; >> syscall_fn f; >> >> kuap_lock(); >> >> + add_random_kstack_offset(); >> regs->orig_gpr3 = r3; >> >> if (IS_ENABLED(CONFIG_PPC_IRQ_SOFT_MASK_DEBUG)) >> @@ -229,7 +232,21 @@ notrace long system_call_exception(long r3, long r4, long r5, >> f = (void *)sys_call_table[r0]; >> } >> >> - return f(r3, r4, r5, r6, r7, r8); >> + ret = f(r3, r4, r5, r6, r7, r8); >> + /* >> + * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), >> + * so the maximum stack offset is 1k bytes(10 bits). >> + * >> + * The actual entropy will be further reduced by the compiler when >> + * applying stack alignment constraints: the powerpc architecture >> + * may have two kinds of stack alignment(16-bytes and 8-bytes). >> + * >> + * So the resulting 6 or 7 bits of entropy is seen in SP[9:4] or SP[9:3]. >> + * >> + */ >> + choose_random_kstack_offset(mftb()); >> + >> + return ret; >> } >> >> static notrace void booke_load_dbcr0(void)