diff mbox series

[v28,16/32] x86/mm: Update maybe_mkwrite() for shadow stack

Message ID 20210722205219.7934-17-yu-cheng.yu@intel.com (mailing list archive)
State New
Headers show
Series Control-flow Enforcement: Shadow Stack | expand

Commit Message

Yu-cheng Yu July 22, 2021, 8:52 p.m. UTC 
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>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Kees Cook <keescook@chromium.org>
---
 arch/x86/include/asm/pgtable.h |  6 ++++++
 arch/x86/mm/pgtable.c          | 20 ++++++++++++++++++++
 include/linux/mm.h             |  2 ++
 mm/huge_memory.c               |  2 ++
 4 files changed, 30 insertions(+)

Comments

Borislav Petkov Aug. 16, 2021, 5:03 p.m. UTC | #1 
On Thu, Jul 22, 2021 at 01:52:03PM -0700, Yu-cheng Yu wrote:
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index 3364fe62b903..ba449d12ec32 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);

What are all those likely()ies here for?
Yu-cheng Yu Aug. 17, 2021, 6:36 p.m. UTC | #2 
On 8/16/2021 10:03 AM, Borislav Petkov wrote:
> On Thu, Jul 22, 2021 at 01:52:03PM -0700, Yu-cheng Yu wrote:
>> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
>> index 3364fe62b903..ba449d12ec32 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);
> 
> What are all those likely()ies here for?
> 

I will remove those.

Thanks,
Yu-cheng
diff mbox series

Patch

diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index df4ce715560a..bfe4ea2b652d 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -280,6 +280,9 @@  static inline int pmd_trans_huge(pmd_t pmd)
 	return (pmd_val(pmd) & (_PAGE_PSE|_PAGE_DEVMAP)) == _PAGE_PSE;
 }
 
+#define maybe_pmd_mkwrite maybe_pmd_mkwrite
+extern pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma);
+
 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 static inline int pud_trans_huge(pud_t pud)
 {
@@ -1632,6 +1635,9 @@  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);
+
 #endif	/* __ASSEMBLY__ */
 
 #endif /* _ASM_X86_PGTABLE_H */
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 3364fe62b903..ba449d12ec32 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 4a9985e50819..4548f75cef14 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1015,12 +1015,14 @@  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 afff3ac87067..c8dd5913884e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -491,12 +491,14 @@  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)