| Message ID | 20190813205225.12032-16-yu-cheng.yu@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Control-flow Enforcement: Shadow Stack | expand |
On Tue, Aug 13, 2019 at 2:02 PM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote: > > When a task does fork(), its shadow stack (SHSTK) must be duplicated > for the child. This patch implements a flow similar to copy-on-write > of an anonymous page, but for SHSTK. > > A SHSTK PTE must be RO and dirty. This dirty bit requirement is used > to effect the copying. In copy_one_pte(), clear the dirty bit from a > SHSTK PTE to cause a page fault upon the next SHSTK access. At that > time, fix the PTE and copy/re-use the page. Is using VM_SHSTK and special-casing all of this really better than using a special mapping or other pseudo-file-backed VMA and putting all the magic in the vm_operations? --Andy
On Tue, 2019-08-13 at 15:55 -0700, Andy Lutomirski wrote: > On Tue, Aug 13, 2019 at 2:02 PM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote: > > > > When a task does fork(), its shadow stack (SHSTK) must be duplicated > > for the child. This patch implements a flow similar to copy-on-write > > of an anonymous page, but for SHSTK. > > > > A SHSTK PTE must be RO and dirty. This dirty bit requirement is used > > to effect the copying. In copy_one_pte(), clear the dirty bit from a > > SHSTK PTE to cause a page fault upon the next SHSTK access. At that > > time, fix the PTE and copy/re-use the page. > > Is using VM_SHSTK and special-casing all of this really better than > using a special mapping or other pseudo-file-backed VMA and putting > all the magic in the vm_operations? A special mapping is cleaner. However, we also need to exclude normal [RO + dirty] pages from shadow stack. Yu-cheng
On 8/14/19 9:27 AM, Yu-cheng Yu wrote: > On Tue, 2019-08-13 at 15:55 -0700, Andy Lutomirski wrote: >> On Tue, Aug 13, 2019 at 2:02 PM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote: >>> When a task does fork(), its shadow stack (SHSTK) must be duplicated >>> for the child. This patch implements a flow similar to copy-on-write >>> of an anonymous page, but for SHSTK. >>> >>> A SHSTK PTE must be RO and dirty. This dirty bit requirement is used >>> to effect the copying. In copy_one_pte(), clear the dirty bit from a >>> SHSTK PTE to cause a page fault upon the next SHSTK access. At that >>> time, fix the PTE and copy/re-use the page. >> Is using VM_SHSTK and special-casing all of this really better than >> using a special mapping or other pseudo-file-backed VMA and putting >> all the magic in the vm_operations? > A special mapping is cleaner. However, we also need to exclude normal [RO + > dirty] pages from shadow stack. I don't understand what you are saying. Are you saying that we need this VM_SHSTK flag in order to exclude RO+HW-Dirty pages from being created in non-shadow-stack VMAs?
On Wed, 2019-08-14 at 09:48 -0700, Dave Hansen wrote: > On 8/14/19 9:27 AM, Yu-cheng Yu wrote: > > On Tue, 2019-08-13 at 15:55 -0700, Andy Lutomirski wrote: > > > On Tue, Aug 13, 2019 at 2:02 PM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote: > > > > When a task does fork(), its shadow stack (SHSTK) must be duplicated > > > > for the child. This patch implements a flow similar to copy-on-write > > > > of an anonymous page, but for SHSTK. > > > > > > > > A SHSTK PTE must be RO and dirty. This dirty bit requirement is used > > > > to effect the copying. In copy_one_pte(), clear the dirty bit from a > > > > SHSTK PTE to cause a page fault upon the next SHSTK access. At that > > > > time, fix the PTE and copy/re-use the page. > > > > > > Is using VM_SHSTK and special-casing all of this really better than > > > using a special mapping or other pseudo-file-backed VMA and putting > > > all the magic in the vm_operations? > > > > A special mapping is cleaner. However, we also need to exclude normal [RO + > > dirty] pages from shadow stack. > > I don't understand what you are saying. > > Are you saying that we need this VM_SHSTK flag in order to exclude > RO+HW-Dirty pages from being created in non-shadow-stack VMAs? We use VM_SHSTK for page fault handling (the special-casing). If we have a special mapping, all these become cleaner (but more code). However, we still need most of the PTE macros (e.g. ptep_set_wrprotect, PAGE_DIRTY_SW, etc.). Yu-cheng
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c index 44816ff6411f..0c10d0c5e329 100644 --- a/arch/x86/mm/pgtable.c +++ b/arch/x86/mm/pgtable.c @@ -876,3 +876,18 @@ int pmd_free_pte_page(pmd_t *pmd, unsigned long addr) #endif /* CONFIG_X86_64 */ #endif /* CONFIG_HAVE_ARCH_HUGE_VMAP */ + +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER +inline pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma) +{ + if (vma->vm_flags & VM_SHSTK) + return pte_mkdirty_shstk(pte); + else + return pte; +} + +inline bool arch_copy_pte_mapping(vm_flags_t vm_flags) +{ + return (vm_flags & VM_SHSTK); +} +#endif /* CONFIG_X86_INTEL_SHADOW_STACK_USER */ diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h index 75d9d68a6de7..89b0fa132f1f 100644 --- a/include/asm-generic/pgtable.h +++ b/include/asm-generic/pgtable.h @@ -1188,4 +1188,19 @@ static inline bool arch_has_pfn_modify_check(void) #define mm_pmd_folded(mm) __is_defined(__PAGETABLE_PMD_FOLDED) #endif +#ifndef CONFIG_ARCH_HAS_SHSTK +static inline pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma) +{ + return pte; +} + +static inline bool arch_copy_pte_mapping(vm_flags_t vm_flags) +{ + return false; +} +#else +pte_t pte_set_vma_features(pte_t pte, struct vm_area_struct *vma); +bool arch_copy_pte_mapping(vm_flags_t vm_flags); +#endif + #endif /* _ASM_GENERIC_PGTABLE_H */ diff --git a/mm/memory.c b/mm/memory.c index e2bb51b6242e..be93a73b5152 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -754,7 +754,8 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm, * If it's a COW mapping, write protect it both * in the parent and the child */ - if (is_cow_mapping(vm_flags) && pte_write(pte)) { + if ((is_cow_mapping(vm_flags) && pte_write(pte)) || + arch_copy_pte_mapping(vm_flags)) { ptep_set_wrprotect(src_mm, addr, src_pte); pte = pte_wrprotect(pte); } @@ -2273,6 +2274,7 @@ static inline void wp_page_reuse(struct vm_fault *vmf) flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte)); entry = pte_mkyoung(vmf->orig_pte); entry = maybe_mkwrite(pte_mkdirty(entry), vma); + entry = pte_set_vma_features(entry, vma); if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1)) update_mmu_cache(vma, vmf->address, vmf->pte); pte_unmap_unlock(vmf->pte, vmf->ptl); @@ -2348,6 +2350,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf) flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte)); entry = mk_pte(new_page, vma->vm_page_prot); entry = maybe_mkwrite(pte_mkdirty(entry), vma); + entry = pte_set_vma_features(entry, vma); /* * Clear the pte entry and flush it first, before updating the * pte with the new entry. This will avoid a race condition @@ -2866,6 +2869,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) pte = mk_pte(page, vma->vm_page_prot); if ((vmf->flags & FAULT_FLAG_WRITE) && reuse_swap_page(page, NULL)) { pte = maybe_mkwrite(pte_mkdirty(pte), vma); + pte = pte_set_vma_features(pte, vma); vmf->flags &= ~FAULT_FLAG_WRITE; ret |= VM_FAULT_WRITE; exclusive = RMAP_EXCLUSIVE; @@ -3008,6 +3012,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) entry = mk_pte(page, vma->vm_page_prot); if (vma->vm_flags & VM_WRITE) entry = pte_mkwrite(pte_mkdirty(entry)); + entry = pte_set_vma_features(entry, vma); vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address, &vmf->ptl);
When a task does fork(), its shadow stack (SHSTK) must be duplicated for the child. This patch implements a flow similar to copy-on-write of an anonymous page, but for SHSTK. A SHSTK PTE must be RO and dirty. This dirty bit requirement is used to effect the copying. In copy_one_pte(), clear the dirty bit from a SHSTK PTE to cause a page fault upon the next SHSTK access. At that time, fix the PTE and copy/re-use the page. Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> --- arch/x86/mm/pgtable.c | 15 +++++++++++++++ include/asm-generic/pgtable.h | 15 +++++++++++++++ mm/memory.c | 7 ++++++- 3 files changed, 36 insertions(+), 1 deletion(-)