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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id bv21sm6698862pjb.15.2021.02.04.12.10.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Feb 2021 12:10:16 -0800 (PST) Date: Thu, 4 Feb 2021 12:10:15 -0800 From: Kees Cook To: Yu-cheng Yu Cc: x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, Arnd Bergmann , Andy Lutomirski , Balbir Singh , Borislav Petkov , Cyrill Gorcunov , Dave Hansen , Eugene Syromiatnikov , Florian Weimer , "H.J. Lu" , Jann Horn , Jonathan Corbet , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , Vedvyas Shanbhogue , Dave Martin , Weijiang Yang , Pengfei Xu , Christoph Hellwig Subject: Re: [PATCH v19 07/25] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Message-ID: <202102041209.B1A0FF3D@keescook> References: <20210203225547.32221-1-yu-cheng.yu@intel.com> <20210203225547.32221-8-yu-cheng.yu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210203225547.32221-8-yu-cheng.yu@intel.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Feb 03, 2021 at 02:55:29PM -0800, Yu-cheng Yu wrote: > The x86 family of processors do not directly create read-only and Dirty > PTEs. These PTEs are created by software. One such case is that kernel > read-only pages are historically setup as Dirty. > > New processors that support Shadow Stack regard read-only and Dirty PTEs as > shadow stack pages. This results in ambiguity between shadow stack and > kernel read-only pages. To resolve this, removed Dirty from kernel read- > only pages. Does this have any other side-effects? Otherwise, sure: Reviewed-by: Kees Cook -Kees > > Signed-off-by: Yu-cheng Yu > Cc: "H. Peter Anvin" > Cc: Kees Cook > Cc: Thomas Gleixner > Cc: Dave Hansen > Cc: Christoph Hellwig > Cc: Andy Lutomirski > Cc: Ingo Molnar > Cc: Borislav Petkov > Cc: Peter Zijlstra > --- > arch/x86/include/asm/pgtable_types.h | 6 +++--- > arch/x86/mm/pat/set_memory.c | 2 +- > 2 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h > index 394757ee030a..b8b79d618bbc 100644 > --- a/arch/x86/include/asm/pgtable_types.h > +++ b/arch/x86/include/asm/pgtable_types.h > @@ -194,10 +194,10 @@ enum page_cache_mode { > #define _KERNPG_TABLE (__PP|__RW| 0|___A| 0|___D| 0| 0| _ENC) > #define _PAGE_TABLE_NOENC (__PP|__RW|_USR|___A| 0|___D| 0| 0) > #define _PAGE_TABLE (__PP|__RW|_USR|___A| 0|___D| 0| 0| _ENC) > -#define __PAGE_KERNEL_RO (__PP| 0| 0|___A|__NX|___D| 0|___G) > -#define __PAGE_KERNEL_ROX (__PP| 0| 0|___A| 0|___D| 0|___G) > +#define __PAGE_KERNEL_RO (__PP| 0| 0|___A|__NX| 0| 0|___G) > +#define __PAGE_KERNEL_ROX (__PP| 0| 0|___A| 0| 0| 0|___G) > #define __PAGE_KERNEL_NOCACHE (__PP|__RW| 0|___A|__NX|___D| 0|___G| __NC) > -#define __PAGE_KERNEL_VVAR (__PP| 0|_USR|___A|__NX|___D| 0|___G) > +#define __PAGE_KERNEL_VVAR (__PP| 0|_USR|___A|__NX| 0| 0|___G) > #define __PAGE_KERNEL_LARGE (__PP|__RW| 0|___A|__NX|___D|_PSE|___G) > #define __PAGE_KERNEL_LARGE_EXEC (__PP|__RW| 0|___A| 0|___D|_PSE|___G) > #define __PAGE_KERNEL_WP (__PP|__RW| 0|___A|__NX|___D| 0|___G| __WP) > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c > index 16f878c26667..6bebb95a6988 100644 > --- a/arch/x86/mm/pat/set_memory.c > +++ b/arch/x86/mm/pat/set_memory.c > @@ -1932,7 +1932,7 @@ int set_memory_nx(unsigned long addr, int numpages) > > int set_memory_ro(unsigned long addr, int numpages) > { > - return change_page_attr_clear(&addr, numpages, __pgprot(_PAGE_RW), 0); > + return change_page_attr_clear(&addr, numpages, __pgprot(_PAGE_RW | _PAGE_DIRTY), 0); > } > > int set_memory_rw(unsigned long addr, int numpages) > -- > 2.21.0 > -- Kees Cook