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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id v7sm17487346pfn.61.2020.02.25.12.07.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Feb 2020 12:07:51 -0800 (PST) Date: Tue, 25 Feb 2020 12:07:50 -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 , x86-patch-review@intel.com Subject: Re: [RFC PATCH v9 06/27] mm: Introduce VM_SHSTK for Shadow Stack memory Message-ID: <202002251207.8EB036A712@keescook> References: <20200205181935.3712-1-yu-cheng.yu@intel.com> <20200205181935.3712-7-yu-cheng.yu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200205181935.3712-7-yu-cheng.yu@intel.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 05, 2020 at 10:19:14AM -0800, Yu-cheng Yu wrote: > A Shadow Stack (SHSTK) PTE must be read-only and have _PAGE_DIRTY set. > However, read-only and Dirty PTEs also exist for copy-on-write (COW) pages. > These two cases are handled differently for page faults and a new VM flag > is necessary for tracking SHSTK VMAs. > > v9: > - Add VM_SHSTK case to arch_vma_name(). > - Revise the commit log to explain why a new VM flag is needed. > > Signed-off-by: Yu-cheng Yu Reviewed-by: Kees Cook -Kees > --- > arch/x86/mm/mmap.c | 2 ++ > fs/proc/task_mmu.c | 3 +++ > include/linux/mm.h | 8 ++++++++ > 3 files changed, 13 insertions(+) > > diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c > index aae9a933dfd4..482813b4c659 100644 > --- a/arch/x86/mm/mmap.c > +++ b/arch/x86/mm/mmap.c > @@ -165,6 +165,8 @@ const char *arch_vma_name(struct vm_area_struct *vma) > { > if (vma->vm_flags & VM_MPX) > return "[mpx]"; > + else if (vma->vm_flags & VM_SHSTK) > + return "[shadow stack]"; > return NULL; > } > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index 9442631fd4af..590b58ee008a 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -687,6 +687,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma) > [ilog2(VM_PKEY_BIT4)] = "", > #endif > #endif /* CONFIG_ARCH_HAS_PKEYS */ > +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER > + [ilog2(VM_SHSTK)] = "ss", > +#endif > }; > size_t i; > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index cfaa8feecfe8..b5145fbe102e 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -298,11 +298,13 @@ extern unsigned int kobjsize(const void *objp); > #define VM_HIGH_ARCH_BIT_2 34 /* bit only usable on 64-bit architectures */ > #define VM_HIGH_ARCH_BIT_3 35 /* bit only usable on 64-bit architectures */ > #define VM_HIGH_ARCH_BIT_4 36 /* bit only usable on 64-bit architectures */ > +#define VM_HIGH_ARCH_BIT_5 37 /* bit only usable on 64-bit architectures */ > #define VM_HIGH_ARCH_0 BIT(VM_HIGH_ARCH_BIT_0) > #define VM_HIGH_ARCH_1 BIT(VM_HIGH_ARCH_BIT_1) > #define VM_HIGH_ARCH_2 BIT(VM_HIGH_ARCH_BIT_2) > #define VM_HIGH_ARCH_3 BIT(VM_HIGH_ARCH_BIT_3) > #define VM_HIGH_ARCH_4 BIT(VM_HIGH_ARCH_BIT_4) > +#define VM_HIGH_ARCH_5 BIT(VM_HIGH_ARCH_BIT_5) > #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */ > > #ifdef CONFIG_ARCH_HAS_PKEYS > @@ -340,6 +342,12 @@ extern unsigned int kobjsize(const void *objp); > # define VM_MPX VM_NONE > #endif > > +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER > +# define VM_SHSTK VM_HIGH_ARCH_5 > +#else > +# define VM_SHSTK VM_NONE > +#endif > + > #ifndef VM_GROWSUP > # define VM_GROWSUP VM_NONE > #endif > -- > 2.21.0 > -- Kees Cook