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 BE751C433FE for ; Mon, 14 Nov 2022 14:37:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236830AbiKNOhc (ORCPT ); Mon, 14 Nov 2022 09:37:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45036 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236976AbiKNOhV (ORCPT ); Mon, 14 Nov 2022 09:37:21 -0500 Received: from relay2-d.mail.gandi.net (relay2-d.mail.gandi.net [IPv6:2001:4b98:dc4:8::222]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7E4F82A720 for ; Mon, 14 Nov 2022 06:37:13 -0800 (PST) Received: (Authenticated sender: alex@ghiti.fr) by mail.gandi.net (Postfix) with ESMTPSA id 63D1140002; Mon, 14 Nov 2022 14:37:10 +0000 (UTC) Message-ID: Date: Mon, 14 Nov 2022 15:37:10 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.2 Subject: Re: [PATCH] riscv: mm: Proper page permissions after initmem free Content-Language: en-US To: =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv@lists.infradead.org Cc: =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , linux-kernel@vger.kernel.org References: <20221112113543.3165646-1-bjorn@kernel.org> From: Alexandre Ghiti In-Reply-To: <20221112113543.3165646-1-bjorn@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Björn, On 12/11/2022 12:35, Björn Töpel wrote: > From: Björn Töpel > > 64-bit RISC-V kernels have the kernel image mapped separately, and in > addition to the linear map. When the kernel is loaded, the linear map > of kernel image is set to PAGE_READ permission, and the kernel map is > set to PAGE_READ and PAGE_EXEC. > > When the initmem is freed, the corresponding pages in the linear map > should be restored to PAGE_READ and PAGE_WRITE. The corresponding > pages in the kernel map should also be restored to PAGE_READ and > PAGE_WRITE, by removing the PAGE_EXEC permission, and adding > PAGE_WRITE. > > This is not the case. For 64-bit kernels, only the linear map is > restored to its proper page permissions at initmem free, and not the > kernelmap. > > In practise this results in that the kernel can potentially jump to > dead __init code, and start executing invalid 0xcc instructions, > without getting an exception. > > Restore the freed initmem properly, by setting both the alias (kernel > map) and the linear map to the correct permissions. > > Fixes: e5c35fa04019 ("riscv: Map the kernel with correct permissions the first time") > Signed-off-by: Björn Töpel > --- > arch/riscv/kernel/setup.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c > index ad76bb59b059..361e635070fe 100644 > --- a/arch/riscv/kernel/setup.c > +++ b/arch/riscv/kernel/setup.c > @@ -321,10 +321,12 @@ subsys_initcall(topology_init); > > void free_initmem(void) > { > - if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX)) > - set_kernel_memory(lm_alias(__init_begin), lm_alias(__init_end), > - IS_ENABLED(CONFIG_64BIT) ? > - set_memory_rw : set_memory_rw_nx); > + if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX)) { > + if (IS_ENABLED(CONFIG_64BIT)) > + set_kernel_memory(lm_alias(__init_begin), lm_alias(__init_end), > + set_memory_rw); > + set_kernel_memory(__init_begin, __init_end, set_memory_rw_nx); That's nits but for 64-bit kernels, do we really want to make the kernel mapping writable? I think catching a write access here would be better because IMO that should not happen. Thanks, Alex > + } > > free_initmem_default(POISON_FREE_INITMEM); > } > > base-commit: 442bcbfd2c5401587b983e34bed0b407214735c3