From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f70.google.com (mail-pl0-f70.google.com [209.85.160.70]) by kanga.kvack.org (Postfix) with ESMTP id 427CC6B0022 for ; Fri, 6 Apr 2018 16:58:12 -0400 (EDT) Received: by mail-pl0-f70.google.com with SMTP id f3-v6so1756026plf.1 for ; Fri, 06 Apr 2018 13:58:12 -0700 (PDT) Received: from mga07.intel.com (mga07.intel.com. [134.134.136.100]) by mx.google.com with ESMTPS id w19si7500823pgv.805.2018.04.06.13.58.10 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 06 Apr 2018 13:58:11 -0700 (PDT) Subject: [PATCH 08/11] x86/mm: do not forbid _PAGE_RW before init for __ro_after_init From: Dave Hansen Date: Fri, 06 Apr 2018 13:55:14 -0700 References: <20180406205501.24A1A4E7@viggo.jf.intel.com> In-Reply-To: <20180406205501.24A1A4E7@viggo.jf.intel.com> Message-Id: <20180406205514.8D898241@viggo.jf.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Dave Hansen , keescook@chromium.org, aarcange@redhat.com, luto@kernel.org, torvalds@linux-foundation.org, hughd@google.com, jgross@suse.com, x86@kernel.org, namit@vmware.com From: Dave Hansen __ro_after_init data gets stuck in the .rodata section. That's normally fine because the kernel itself manages the R/W properties. But, if we run __change_page_attr() on an area which is __ro_after_init, the .rodata checks will trigger and force the area to be immediately read-only, even if it is early-ish in boot. This caused problems when trying to clear the _PAGE_GLOBAL bit for these area in the PTI code: it cleared _PAGE_GLOBAL like I asked, but also took it up on itself to clear _PAGE_RW. The kernel then oopses the next time it wrote to a __ro_after_init data structure. To fix this, add the kernel_set_to_readonly check, just like we have for kernel text, just a few lines below in this function. Signed-off-by: Dave Hansen Acked-by: Kees Cook Cc: Andrea Arcangeli Cc: Andy Lutomirski Cc: Linus Torvalds Cc: Hugh Dickins Cc: Juergen Gross Cc: x86@kernel.org Cc: Nadav Amit --- b/arch/x86/mm/pageattr.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff -puN arch/x86/mm/pageattr.c~check-kernel_set_to_readonly arch/x86/mm/pageattr.c --- a/arch/x86/mm/pageattr.c~check-kernel_set_to_readonly 2018-04-06 10:47:57.711796120 -0700 +++ b/arch/x86/mm/pageattr.c 2018-04-06 10:47:57.714796120 -0700 @@ -298,9 +298,11 @@ static inline pgprot_t static_protection /* * The .rodata section needs to be read-only. Using the pfn - * catches all aliases. + * catches all aliases. This also includes __ro_after_init, + * so do not enforce until kernel_set_to_readonly is true. */ - if (within(pfn, __pa_symbol(__start_rodata) >> PAGE_SHIFT, + if (kernel_set_to_readonly && + within(pfn, __pa_symbol(__start_rodata) >> PAGE_SHIFT, __pa_symbol(__end_rodata) >> PAGE_SHIFT)) pgprot_val(forbidden) |= _PAGE_RW; _