mm: vmalloc must set pte via arch code

Patch series "Fixes for pte encapsulation bypasses", v3.

A series to improve the encapsulation of pte entries by disallowing
non-arch code from directly dereferencing pte_t pointers.


This patch (of 4):

It is bad practice to directly set pte entries within a pte table. 
Instead all modifications must go through arch-provided helpers such as
set_pte_at() to give the arch code visibility and allow it to check (and
potentially modify) the operation.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 3e9a9e256b1e ("mm: add a vmap_pfn function")
Signed-off-by: Ryan Roberts <[email protected]>
Reviewed-by: Zi Yan <[email protected]>
Acked-by: Lorenzo Stoakes <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Uladzislau Rezki (Sony) <[email protected]>
Reviewed-by: Mike Rapoport (IBM) <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: SeongJae Park <[email protected]>
Cc: Yu Zhao <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 8 insertions, 2 deletions

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 7c32435219b1..9d64a4098c36 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2944,10 +2944,16 @@ struct vmap_pfn_data {
 static int vmap_pfn_apply(pte_t *pte, unsigned long addr, void *private)
 {
 	struct vmap_pfn_data *data = private;
+	unsigned long pfn = data->pfns[data->idx];
+	pte_t ptent;
 
-	if (WARN_ON_ONCE(pfn_valid(data->pfns[data->idx])))
+	if (WARN_ON_ONCE(pfn_valid(pfn)))
 		return -EINVAL;
-	*pte = pte_mkspecial(pfn_pte(data->pfns[data->idx++], data->prot));
+
+	ptent = pte_mkspecial(pfn_pte(pfn, data->prot));
+	set_pte_at(&init_mm, addr, pte, ptent);
+
+	data->idx++;
 	return 0;
 }