| Message ID | 20210316151054.5405-18-yu-cheng.yu@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Control-flow Enforcement: Shadow Stack | expand |
On Tue, Mar 16, 2021 at 08:10:43AM -0700, Yu-cheng Yu wrote: > INCSSP(Q/D) increments shadow stack pointer and 'pops and discards' the > first and the last elements in the range, effectively touches those memory > areas. > > The maximum moving distance by INCSSPQ is 255 * 8 = 2040 bytes and > 255 * 4 = 1020 bytes by INCSSPD. Both ranges are far from PAGE_SIZE. > Thus, putting a gap page on both ends of a shadow stack prevents INCSSP, > CALL, and RET from going beyond. > > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> > Reviewed-by: Kees Cook <keescook@chromium.org> > --- > arch/x86/include/asm/page_64_types.h | 10 ++++++++++ > include/linux/mm.h | 24 ++++++++++++++++++++---- > 2 files changed, 30 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h > index 64297eabad63..23e3d880ce6c 100644 > --- a/arch/x86/include/asm/page_64_types.h > +++ b/arch/x86/include/asm/page_64_types.h > @@ -115,4 +115,14 @@ > #define KERNEL_IMAGE_SIZE (512 * 1024 * 1024) > #endif > > +/* > + * Shadow stack pointer is moved by CALL, RET, and INCSSP(Q/D). INCSSPQ > + * moves shadow stack pointer up to 255 * 8 = ~2 KB (~1KB for INCSSPD) and > + * touches the first and the last element in the range, which triggers a > + * page fault if the range is not in a shadow stack. Because of this, > + * creating 4-KB guard pages around a shadow stack prevents these > + * instructions from going beyond. > + */ > +#define ARCH_SHADOW_STACK_GUARD_GAP PAGE_SIZE > + > #endif /* _ASM_X86_PAGE_64_DEFS_H */ > diff --git a/include/linux/mm.h b/include/linux/mm.h > index af805ffde48e..9890e9f5a5e0 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2619,6 +2619,10 @@ extern vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf); > int __must_check write_one_page(struct page *page); > void task_dirty_inc(struct task_struct *tsk); > > +#ifndef ARCH_SHADOW_STACK_GUARD_GAP > +#define ARCH_SHADOW_STACK_GUARD_GAP 0 > +#endif > + > extern unsigned long stack_guard_gap; > /* Generic expand stack which grows the stack according to GROWS{UP,DOWN} */ > extern int expand_stack(struct vm_area_struct *vma, unsigned long address); > @@ -2651,9 +2655,15 @@ static inline struct vm_area_struct * find_vma_intersection(struct mm_struct * m > static inline unsigned long vm_start_gap(struct vm_area_struct *vma) > { > unsigned long vm_start = vma->vm_start; > + unsigned long gap = 0; > > - if (vma->vm_flags & VM_GROWSDOWN) { > - vm_start -= stack_guard_gap; > + if (vma->vm_flags & VM_GROWSDOWN) > + gap = stack_guard_gap; > + else if (vma->vm_flags & VM_SHSTK) > + gap = ARCH_SHADOW_STACK_GUARD_GAP; Looks too x86-centric for generic code. Maybe we can have a helper that would return gap for the given VMA? The generic version of the helper would only return stack_guard_gap for VM_GROWSDOWN. Arch code would override it to handle VM_SHSTK case too. Similar can be done in vm_end_gap(). > + > + if (gap != 0) { > + vm_start -= gap; > if (vm_start > vma->vm_start) > vm_start = 0; > } > @@ -2663,9 +2673,15 @@ static inline unsigned long vm_start_gap(struct vm_area_struct *vma) > static inline unsigned long vm_end_gap(struct vm_area_struct *vma) > { > unsigned long vm_end = vma->vm_end; > + unsigned long gap = 0; > + > + if (vma->vm_flags & VM_GROWSUP) > + gap = stack_guard_gap; > + else if (vma->vm_flags & VM_SHSTK) > + gap = ARCH_SHADOW_STACK_GUARD_GAP; > > - if (vma->vm_flags & VM_GROWSUP) { > - vm_end += stack_guard_gap; > + if (gap != 0) { > + vm_end += gap; > if (vm_end < vma->vm_end) > vm_end = -PAGE_SIZE; > } > -- > 2.21.0 >
diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h index 64297eabad63..23e3d880ce6c 100644 --- a/arch/x86/include/asm/page_64_types.h +++ b/arch/x86/include/asm/page_64_types.h @@ -115,4 +115,14 @@ #define KERNEL_IMAGE_SIZE (512 * 1024 * 1024) #endif +/* + * Shadow stack pointer is moved by CALL, RET, and INCSSP(Q/D). INCSSPQ + * moves shadow stack pointer up to 255 * 8 = ~2 KB (~1KB for INCSSPD) and + * touches the first and the last element in the range, which triggers a + * page fault if the range is not in a shadow stack. Because of this, + * creating 4-KB guard pages around a shadow stack prevents these + * instructions from going beyond. + */ +#define ARCH_SHADOW_STACK_GUARD_GAP PAGE_SIZE + #endif /* _ASM_X86_PAGE_64_DEFS_H */ diff --git a/include/linux/mm.h b/include/linux/mm.h index af805ffde48e..9890e9f5a5e0 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2619,6 +2619,10 @@ extern vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf); int __must_check write_one_page(struct page *page); void task_dirty_inc(struct task_struct *tsk); +#ifndef ARCH_SHADOW_STACK_GUARD_GAP +#define ARCH_SHADOW_STACK_GUARD_GAP 0 +#endif + extern unsigned long stack_guard_gap; /* Generic expand stack which grows the stack according to GROWS{UP,DOWN} */ extern int expand_stack(struct vm_area_struct *vma, unsigned long address); @@ -2651,9 +2655,15 @@ static inline struct vm_area_struct * find_vma_intersection(struct mm_struct * m static inline unsigned long vm_start_gap(struct vm_area_struct *vma) { unsigned long vm_start = vma->vm_start; + unsigned long gap = 0; - if (vma->vm_flags & VM_GROWSDOWN) { - vm_start -= stack_guard_gap; + if (vma->vm_flags & VM_GROWSDOWN) + gap = stack_guard_gap; + else if (vma->vm_flags & VM_SHSTK) + gap = ARCH_SHADOW_STACK_GUARD_GAP; + + if (gap != 0) { + vm_start -= gap; if (vm_start > vma->vm_start) vm_start = 0; } @@ -2663,9 +2673,15 @@ static inline unsigned long vm_start_gap(struct vm_area_struct *vma) static inline unsigned long vm_end_gap(struct vm_area_struct *vma) { unsigned long vm_end = vma->vm_end; + unsigned long gap = 0; + + if (vma->vm_flags & VM_GROWSUP) + gap = stack_guard_gap; + else if (vma->vm_flags & VM_SHSTK) + gap = ARCH_SHADOW_STACK_GUARD_GAP; - if (vma->vm_flags & VM_GROWSUP) { - vm_end += stack_guard_gap; + if (gap != 0) { + vm_end += gap; if (vm_end < vma->vm_end) vm_end = -PAGE_SIZE; }