linux-kernel - [PATCH] mm/memory.c: make remap_pfn

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Message-Id: <20200617233512.177519-1-zhangalex@google.com>
Date:   Wed, 17 Jun 2020 16:35:12 -0700
From:   Kaiyu Zhang <zhangalex@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Alex Zhang <zhangalex@...gle.com>
Subject: [PATCH] mm/memory.c: make remap_pfn_range() reject unaligned addr

From: Alex Zhang <zhangalex@...gle.com>

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@...gle.com>

---
 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