Messages in this thread | | | Date | Mon, 20 Feb 2023 13:56:07 +0100 | Subject | Re: [PATCH v6 18/41] mm: Introduce VM_SHADOW_STACK for shadow stack memory | From | David Hildenbrand <> |
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On 18.02.23 22:14, Rick Edgecombe wrote: > From: Yu-cheng Yu <yu-cheng.yu@intel.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@chromium.org> > Tested-by: Pengfei Xu <pengfei.xu@intel.com> > Tested-by: John Allen <john.allen@amd.com> > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> > Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com> > Cc: Kees Cook <keescook@chromium.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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