| Message ID | 20210401221104.31584-16-yu-cheng.yu@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v24,01/30] Documentation/x86: Add CET description | expand |
On Thu, Apr 01, 2021 at 03:10:49PM -0700, Yu-cheng Yu wrote: > When serving a page fault, maybe_mkwrite() makes a PTE writable if its vma > has VM_WRITE. > > A shadow stack vma has VM_SHADOW_STACK. Its PTEs have _PAGE_DIRTY, but not > _PAGE_WRITE. In fork(), _PAGE_DIRTY is cleared to cause copy-on-write, > and in the page fault handler, _PAGE_DIRTY is restored and the shadow stack > page is writable again. > > Introduce an x86 version of maybe_mkwrite(), which sets proper PTE bits > according to VM flags. > > Apply the same changes to maybe_pmd_mkwrite(). > > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> > Cc: Kees Cook <keescook@chromium.org> > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > --- > v24: > - Instead of doing arch_maybe_mkwrite(), overwrite maybe*_mkwrite() with x86 > versions. > - Change VM_SHSTK to VM_SHADOW_STACK. > > arch/x86/include/asm/pgtable.h | 8 ++++++++ > arch/x86/mm/pgtable.c | 20 ++++++++++++++++++++ > include/linux/mm.h | 2 ++ > mm/huge_memory.c | 2 ++ > 4 files changed, 32 insertions(+) > > diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h > index 46d9394b884f..51cdf14488b7 100644 > --- a/arch/x86/include/asm/pgtable.h > +++ b/arch/x86/include/asm/pgtable.h > @@ -1686,6 +1686,14 @@ static inline bool arch_faults_on_old_pte(void) > return false; > } > > +#define maybe_mkwrite maybe_mkwrite > +extern pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma); > + > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > +#define maybe_pmd_mkwrite maybe_pmd_mkwrite > +extern pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma); > +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */ Move it next to other THP-depended stuff. Otherwise looks good to me: Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h index 46d9394b884f..51cdf14488b7 100644 --- a/arch/x86/include/asm/pgtable.h +++ b/arch/x86/include/asm/pgtable.h @@ -1686,6 +1686,14 @@ static inline bool arch_faults_on_old_pte(void) return false; } +#define maybe_mkwrite maybe_mkwrite +extern pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma); + +#ifdef CONFIG_TRANSPARENT_HUGEPAGE +#define maybe_pmd_mkwrite maybe_pmd_mkwrite +extern pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma); +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */ + #endif /* __ASSEMBLY__ */ #endif /* _ASM_X86_PGTABLE_H */ diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c index f6a9e2e36642..e778dbbef3d8 100644 --- a/arch/x86/mm/pgtable.c +++ b/arch/x86/mm/pgtable.c @@ -610,6 +610,26 @@ int pmdp_clear_flush_young(struct vm_area_struct *vma, } #endif +pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma) +{ + if (likely(vma->vm_flags & VM_WRITE)) + pte = pte_mkwrite(pte); + else if (likely(vma->vm_flags & VM_SHADOW_STACK)) + pte = pte_mkwrite_shstk(pte); + return pte; +} + +#ifdef CONFIG_TRANSPARENT_HUGEPAGE +pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma) +{ + if (likely(vma->vm_flags & VM_WRITE)) + pmd = pmd_mkwrite(pmd); + else if (likely(vma->vm_flags & VM_SHADOW_STACK)) + pmd = pmd_mkwrite_shstk(pmd); + return pmd; +} +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */ + /** * reserve_top_address - reserves a hole in the top of kernel address space * @reserve - size of hole to reserve diff --git a/include/linux/mm.h b/include/linux/mm.h index 08282eb2f195..6ac9b3e9a865 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -993,12 +993,14 @@ void free_compound_page(struct page *page); * pte_mkwrite. But get_user_pages can cause write faults for mappings * that do not have writing enabled, when used by access_process_vm. */ +#ifndef maybe_mkwrite static inline pte_t maybe_mkwrite(pte_t pte, struct vm_area_struct *vma) { if (likely(vma->vm_flags & VM_WRITE)) pte = pte_mkwrite(pte); return pte; } +#endif vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page); void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr); diff --git a/mm/huge_memory.c b/mm/huge_memory.c index ae907a9c2050..8203bd6ae4bd 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -478,12 +478,14 @@ static int __init setup_transparent_hugepage(char *str) } __setup("transparent_hugepage=", setup_transparent_hugepage); +#ifndef maybe_pmd_mkwrite pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma) { if (likely(vma->vm_flags & VM_WRITE)) pmd = pmd_mkwrite(pmd); return pmd; } +#endif #ifdef CONFIG_MEMCG static inline struct deferred_split *get_deferred_split_queue(struct page *page)
When serving a page fault, maybe_mkwrite() makes a PTE writable if its vma has VM_WRITE. A shadow stack vma has VM_SHADOW_STACK. Its PTEs have _PAGE_DIRTY, but not _PAGE_WRITE. In fork(), _PAGE_DIRTY is cleared to cause copy-on-write, and in the page fault handler, _PAGE_DIRTY is restored and the shadow stack page is writable again. Introduce an x86 version of maybe_mkwrite(), which sets proper PTE bits according to VM flags. Apply the same changes to maybe_pmd_mkwrite(). Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> Cc: Kees Cook <keescook@chromium.org> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> --- v24: - Instead of doing arch_maybe_mkwrite(), overwrite maybe*_mkwrite() with x86 versions. - Change VM_SHSTK to VM_SHADOW_STACK. arch/x86/include/asm/pgtable.h | 8 ++++++++ arch/x86/mm/pgtable.c | 20 ++++++++++++++++++++ include/linux/mm.h | 2 ++ mm/huge_memory.c | 2 ++ 4 files changed, 32 insertions(+)