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

From: Kaiyu Zhang
Date: Wed Jun 17 2020 - 19:35:20 EST


From: Alex Zhang <zhangalex@xxxxxxxxxx>

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@xxxxxxxxxx>

---
mm/memory.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index dc7f3543b1fd..16422acb6da8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2081,7 +2081,7 @@ 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
@@ -2100,6 +2100,9 @@ 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:
--
2.27.0.111.gc72c7da667-goog