[PATCH 5.4.y 3/4] mm/memory.c: make remap_pfn_range() reject unaligned addr

[Harshvardhan Jha <harshvardhan.j.jha@oracle.com>]

From: Alex Zhang <zhangalex@google.com>

commit 0c4123e3fb82d6014d0a70b52eb38153f658541c upstream

This function implicitly assumes that the addr passed in is page aligned.
A non page aligned addr could ultimately cause a kernel bug in
remap_pte_range as the exit condition in the logic loop may never be
satisfied.  This patch documents the need for the requirement, as well as
explicitly adds a check for it.

Signed-off-by: Alex Zhang <zhangalex@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200617233512.177519-1-zhangalex@google.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 0c4123e3fb82d6014d0a70b52eb38153f658541c)
Signed-off-by: Harshvardhan Jha <harshvardhan.j.jha@oracle.com>
---
 mm/memory.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index 50503743724cc..1d009d3d87b34 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1920,7 +1920,7 @@ static inline int remap_p4d_range(struct mm_struct *mm, pgd_t *pgd,
 /**
  * remap_pfn_range - remap kernel memory to userspace
  * @vma: user vma to map to
- * @addr: target user address to start at
+ * @addr: target page aligned user address to start at
  * @pfn: page frame number of kernel physical memory address
  * @size: size of mapping area
  * @prot: page protection flags for this mapping
@@ -1939,6 +1939,9 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
 	unsigned long remap_pfn = pfn;
 	int err;
 
+	if (WARN_ON_ONCE(!PAGE_ALIGNED(addr)))
+		return -EINVAL;
+
 	/*
 	 * Physically remapped pages are special. Tell the
 	 * rest of the world about it:
-- 
2.46.0