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Message-ID: <366c0af9-850f-24b1-3133-976fa92c51e2@redhat.com>
Date: Mon, 20 Feb 2023 13:56:07 +0100
From: David Hildenbrand <david@...hat.com>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>, x86@...nel.org,
"H . Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org, linux-mm@...ck.org,
linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
Arnd Bergmann <arnd@...db.de>,
Andy Lutomirski <luto@...nel.org>,
Balbir Singh <bsingharora@...il.com>,
Borislav Petkov <bp@...en8.de>,
Cyrill Gorcunov <gorcunov@...il.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Eugene Syromiatnikov <esyr@...hat.com>,
Florian Weimer <fweimer@...hat.com>,
"H . J . Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
Jonathan Corbet <corbet@....net>,
Kees Cook <keescook@...omium.org>,
Mike Kravetz <mike.kravetz@...cle.com>,
Nadav Amit <nadav.amit@...il.com>,
Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
Peter Zijlstra <peterz@...radead.org>,
Randy Dunlap <rdunlap@...radead.org>,
Weijiang Yang <weijiang.yang@...el.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
John Allen <john.allen@....com>, kcc@...gle.com,
eranian@...gle.com, rppt@...nel.org, jamorris@...ux.microsoft.com,
dethoma@...rosoft.com, akpm@...ux-foundation.org,
Andrew.Cooper3@...rix.com, christina.schimpe@...el.com,
debug@...osinc.com
Cc: Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH v6 18/41] mm: Introduce VM_SHADOW_STACK for shadow stack
memory
On 18.02.23 22:14, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@...el.com>
>
> The x86 Control-flow Enforcement Technology (CET) feature includes a new
> type of memory called shadow stack. This shadow stack memory has some
> unusual properties, which requires some core mm changes to function
> properly.
>
> A shadow stack 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. Introduce
> VM_SHADOW_STACK to track shadow stack VMAs.
I suggest simplifying and abstracting that description.
"New hardware extensions implement support for shadow stack memory, such
as x86 Control-flow Enforcement Technology (CET). Let's add a new VM
flag to identify these areas, for example, to be used to properly
indicate shadow stack PTEs to the hardware."
>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Tested-by: Pengfei Xu <pengfei.xu@...el.com>
> Tested-by: John Allen <john.allen@....com>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Cc: Kees Cook <keescook@...omium.org>
>
> ---
> v6:
> - Add comment about VM_SHADOW_STACK not being allowed with VM_SHARED
> (David Hildenbrand)
Might want to add some more meat to the patch description why that is
the case.
>
> v3:
> - Drop arch specific change in arch_vma_name(). The memory can show as
> anonymous (Kirill)
> - Change CONFIG_ARCH_HAS_SHADOW_STACK to CONFIG_X86_USER_SHADOW_STACK
> in show_smap_vma_flags() (Boris)
> ---
> Documentation/filesystems/proc.rst | 1 +
> fs/proc/task_mmu.c | 3 +++
> include/linux/mm.h | 8 ++++++++
> 3 files changed, 12 insertions(+)
>
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index e224b6d5b642..115843e8cce3 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -564,6 +564,7 @@ encoded manner. The codes are the following:
> mt arm64 MTE allocation tags are enabled
> um userfaultfd missing tracking
> uw userfaultfd wr-protect tracking
> + ss shadow stack page
> == =======================================
>
> Note that there is no guarantee that every flag and associated mnemonic will
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index af1c49ae11b1..9e2cefe47749 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -711,6 +711,9 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
> #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
> [ilog2(VM_UFFD_MINOR)] = "ui",
> #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
> +#ifdef CONFIG_X86_USER_SHADOW_STACK
> + [ilog2(VM_SHADOW_STACK)] = "ss",
> +#endif
> };
> size_t i;
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index e6f1789c8e69..76e0a09aeffe 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -315,11 +315,13 @@ 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
> @@ -335,6 +337,12 @@ extern unsigned int kobjsize(const void *objp);
> #endif
> #endif /* CONFIG_ARCH_HAS_PKEYS */
>
> +#ifdef CONFIG_X86_USER_SHADOW_STACK
Should we abstract this to CONFIG_ARCH_USER_SHADOW_STACK, seeing that
other architectures might similarly need it?
--
Thanks,
David / dhildenb
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