On Thu, 2023-03-02 at 13:48 +0100, Borislav Petkov wrote:

On Mon, Feb 27, 2023 at 02:29:30PM -0800, Rick Edgecombe wrote:

quoted

diff --git a/arch/x86/include/asm/pgtable_types.h

b/arch/x86/include/asm/pgtable_types.h
index 0646ad00178b..56b374d1bffb 100644

--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h

@@ -21,7 +21,8 @@
  #define _PAGE_BIT_SOFTW2     10      /* " */
  #define _PAGE_BIT_SOFTW3     11      /* " */
  #define _PAGE_BIT_PAT_LARGE  12      /* On 2MB or 1GB pages */
-#define _PAGE_BIT_SOFTW4     58      /* available for programmer

*/
+#define _PAGE_BIT_SOFTW4     57      /* available for programmer
*/
+#define _PAGE_BIT_SOFTW5     58      /* available for programmer
*/
  #define _PAGE_BIT_PKEY_BIT0  59      /* Protection Keys, bit 1/4
*/
  #define _PAGE_BIT_PKEY_BIT1  60      /* Protection Keys, bit 2/4
*/
  #define _PAGE_BIT_PKEY_BIT2  61      /* Protection Keys, bit 3/4
*/

@@ -34,6 +35,15 @@
  #define _PAGE_BIT_SOFT_DIRTY _PAGE_BIT_SOFTW3 /* software dirty

tracking */
  #define _PAGE_BIT_DEVMAP     _PAGE_BIT_SOFTW4
  
+/*
+ * Indicates a Saved Dirty bit page.
+ */
+#ifdef CONFIG_X86_USER_SHADOW_STACK
+#define _PAGE_BIT_SAVED_DIRTY                _PAGE_BIT_SOFTW5 /*
Saved Dirty bit */
+#else
+#define _PAGE_BIT_SAVED_DIRTY                0
+#endif
+
  /* If _PAGE_BIT_PRESENT is clear, we use these: */
  /* - if the user mapped it with PROT_NONE; pte_present gives true
*/
  #define _PAGE_BIT_PROTNONE   _PAGE_BIT_GLOBAL

@@ -117,6 +127,25 @@
  #define _PAGE_SOFTW4 (_AT(pteval_t, 0))
  #endif
  
+/*
+ * The hardware requires shadow stack to be Write=0,Dirty=1.

However,
+ * there are valid cases where the kernel might create read-only
PTEs that
+ * are dirty (e.g., fork(), mprotect(), uffd-wp(), soft-dirty 
tracking). In
+ * this case, the _PAGE_SAVED_DIRTY bit is used instead of the HW-
dirty bit,
+ * to avoid creating a wrong "shadow stack" PTEs. Such PTEs have
+ * (Write=0,SavedDirty=1,Dirty=0) set.
+ *
+ * Note that on processors without shadow stack support, the 

.git/rebase-apply/patch:154: trailing whitespace.
 * Note that on processors without shadow stack support, the 
warning: 1 line adds whitespace errors.

Hm, apparently git checks for that too - not only trailing empty
lines.

Weird. And oops on the space. Just wondering how checkpatch missed
this. It didn't, just was in a pile of false positives on that patch
and I didn't notice it in there.