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-rw-r--r--fs/exec.c7
-rw-r--r--include/linux/mm.h3
-rw-r--r--mm/rmap.c30
3 files changed, 38 insertions, 2 deletions
diff --git a/fs/exec.c b/fs/exec.c
index e6e94c6..9badbc0 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -242,9 +242,10 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
* use STACK_TOP because that can depend on attributes which aren't
* configured yet.
*/
+ BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP);
vma->vm_end = STACK_TOP_MAX;
vma->vm_start = vma->vm_end - PAGE_SIZE;
- vma->vm_flags = VM_STACK_FLAGS;
+ vma->vm_flags = VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
INIT_LIST_HEAD(&vma->anon_vma_chain);
err = insert_vm_struct(mm, vma);
@@ -616,6 +617,7 @@ int setup_arg_pages(struct linux_binprm *bprm,
else if (executable_stack == EXSTACK_DISABLE_X)
vm_flags &= ~VM_EXEC;
vm_flags |= mm->def_flags;
+ vm_flags |= VM_STACK_INCOMPLETE_SETUP;
ret = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end,
vm_flags);
@@ -630,6 +632,9 @@ int setup_arg_pages(struct linux_binprm *bprm,
goto out_unlock;
}
+ /* mprotect_fixup is overkill to remove the temporary stack flags */
+ vma->vm_flags &= ~VM_STACK_INCOMPLETE_SETUP;
+
stack_expand = 131072UL; /* randomly 32*4k (or 2*64k) pages */
stack_size = vma->vm_end - vma->vm_start;
/*
diff --git a/include/linux/mm.h b/include/linux/mm.h
index fb19bb9..98ea5ba 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -106,6 +106,9 @@ extern unsigned int kobjsize(const void *objp);
#define VM_PFN_AT_MMAP 0x40000000 /* PFNMAP vma that is fully mapped at mmap time */
#define VM_MERGEABLE 0x80000000 /* KSM may merge identical pages */
+/* Bits set in the VMA until the stack is in its final location */
+#define VM_STACK_INCOMPLETE_SETUP (VM_RAND_READ | VM_SEQ_READ)
+
#ifndef VM_STACK_DEFAULT_FLAGS /* arch can override this */
#define VM_STACK_DEFAULT_FLAGS VM_DATA_DEFAULT_FLAGS
#endif
diff --git a/mm/rmap.c b/mm/rmap.c
index b5c320f..38a336e 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1131,6 +1131,20 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
return ret;
}
+static bool is_vma_temporary_stack(struct vm_area_struct *vma)
+{
+ int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);
+
+ if (!maybe_stack)
+ return false;
+
+ if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) ==
+ VM_STACK_INCOMPLETE_SETUP)
+ return true;
+
+ return false;
+}
+
/**
* try_to_unmap_anon - unmap or unlock anonymous page using the object-based
* rmap method
@@ -1159,7 +1173,21 @@ static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
struct vm_area_struct *vma = avc->vma;
- unsigned long address = vma_address(page, vma);
+ unsigned long address;
+
+ /*
+ * During exec, a temporary VMA is setup and later moved.
+ * The VMA is moved under the anon_vma lock but not the
+ * page tables leading to a race where migration cannot
+ * find the migration ptes. Rather than increasing the
+ * locking requirements of exec(), migration skips
+ * temporary VMAs until after exec() completes.
+ */
+ if (PAGE_MIGRATION && (flags & TTU_MIGRATION) &&
+ is_vma_temporary_stack(vma))
+ continue;
+
+ address = vma_address(page, vma);
if (address == -EFAULT)
continue;
ret = try_to_unmap_one(page, vma, address, flags);