mm: introduce MADV_DOEXEC

madvise MADV_DOEXEC preserves a memory range across exec.  Initially
only supported for non-executable, non-stack, anonymous memory.
MADV_DOEXEC is single-use and after exec madvise must done again to
preserve memory for a subsequent exec.
MADV_DONTEXEC reverts the effect of a previous MADV_DOXEXEC call and
undoes the preservation of the range.

Orabug: 32387875
Signed-off-by: Steve Sistare <[email protected]>
Signed-off-by: Anthony Yznaga <[email protected]>
Reviewed-by: Liam R. Howlett <[email protected]>

Author: Steve Sistare

include/uapi/asm-generic/mman-common.h

@@ -76,6 +76,9 @@
 #define MADV_POPULATE_READ	22	/* populate (prefault) page tables readable */
 #define MADV_POPULATE_WRITE	23	/* populate (prefault) page tables writable */
 
+#define MADV_DOEXEC	24		/* do inherit across exec */
+#define MADV_DONTEXEC	25		/* don't inherit across exec */
+
 /* compatibility flags */
 #define MAP_FILE	0
 

mm/madvise.c

@@ -106,6 +106,26 @@ static long madvise_behavior(struct vm_area_struct *vma,
 	case MADV_KEEPONFORK:
 		new_flags &= ~VM_WIPEONFORK;
 		break;
+	case MADV_DOEXEC:
+		/*
+		 * MADV_DOEXEC is only supported on private, non-executable,
+		 * non-stack anonymous memory and if the VM_EXEC_KEEP flag
+		 * is available.
+		 */
+		if (!VM_EXEC_KEEP || !vma_is_anonymous(vma) || vma->vm_flags & (VM_EXEC|VM_SHARED|VM_STACK)) {
+			error = -EINVAL;
+			goto out;
+		}
+		new_flags |= (new_flags & ~VM_MAYEXEC) | VM_EXEC_KEEP;
+		break;
+	case MADV_DONTEXEC:
+		if (!VM_EXEC_KEEP) {
+			error = -EINVAL;
+			goto out;
+		}
+		if (new_flags & VM_EXEC_KEEP)
+			new_flags |= (new_flags & ~VM_EXEC_KEEP) | VM_MAYEXEC;
+		break;
 	case MADV_DONTDUMP:
 		new_flags |= VM_DONTDUMP;
 		break;
@@ -1035,6 +1055,8 @@ madvise_behavior_valid(int behavior)
 	case MADV_SOFT_OFFLINE:
 	case MADV_HWPOISON:
 #endif
+	case MADV_DOEXEC:
+	case MADV_DONTEXEC:
 		return true;
 
 	default:
@@ -1111,6 +1133,9 @@ process_madvise_behavior_valid(int behavior)
  *		triggering read faults if required
  *  MADV_POPULATE_WRITE - populate (prefault) page tables writable by
  *		triggering write faults if required
+ *  MADV_DOEXEC - On exec, preserve and duplicate this area in the new process
+ *		if the new process allows it.
+ *  MADV_DONTEXEC - Undo the effect of MADV_DOEXEC.
  *
  * return values:
  *  zero    - success