[RFC PATCH 2/5] mm: mremap: Use round_hint_to_min() for new_addr hints

[Brian Geffon]

MREMAP_DONTUNMAP allows for a get_unmapped_area() hint
when used without MREMAP_FIXED. This was behavior was introduced
inadvertently and should be rounded to the mmap_min_address like
in mmap(2).

Signed-off-by: Brian Geffon <bgeffon@xxxxxxxxxx>
---
 include/linux/mm_inline.h | 14 ++++++++++++++
 mm/mmap.c                 | 13 -------------
 mm/mremap.c               |  3 +++
 3 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index 1b6a917fffa4..863143ec5bb0 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -9,6 +9,7 @@
 #include <linux/string.h>
 #include <linux/userfaultfd_k.h>
 #include <linux/swapops.h>
+#include <linux/security.h>
 
 /**
  * folio_is_file_lru - Should the folio be on a file LRU or anon LRU?
@@ -613,4 +614,17 @@ static inline bool vma_has_recency(struct vm_area_struct *vma)
 	return true;
 }
 
+/*
+ * If a hint addr is less than mmap_min_addr change hint to be as
+ * low as possible but still greater than mmap_min_addr
+ */
+static inline unsigned long round_hint_to_min(unsigned long hint)
+{
+	hint &= PAGE_MASK;
+	if (((void *)hint != NULL) &&
+	    (hint < mmap_min_addr))
+		return PAGE_ALIGN(mmap_min_addr);
+	return hint;
+}
+
 #endif
diff --git a/mm/mmap.c b/mm/mmap.c
index d32b7e701058..04952ac21d58 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -215,19 +215,6 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
 	return origbrk;
 }
 
-/*
- * If a hint addr is less than mmap_min_addr change hint to be as
- * low as possible but still greater than mmap_min_addr
- */
-static inline unsigned long round_hint_to_min(unsigned long hint)
-{
-	hint &= PAGE_MASK;
-	if (((void *)hint != NULL) &&
-	    (hint < mmap_min_addr))
-		return PAGE_ALIGN(mmap_min_addr);
-	return hint;
-}
-
 bool mlock_future_ok(struct mm_struct *mm, unsigned long flags,
 			unsigned long bytes)
 {
diff --git a/mm/mremap.c b/mm/mremap.c
index 62aec72bbe42..fdc1b0f1b38e 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -1109,6 +1109,9 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 			goto out;
 	}
 
+	if (!(flags & MREMAP_FIXED))
+		new_addr = round_hint_to_min(new_addr);
+
 	if (flags & (MREMAP_FIXED | MREMAP_DONTUNMAP)) {
 		ret = mremap_to(addr, old_len, new_addr, new_len,
 				&locked, flags, &uf, &uf_unmap_early,
-- 
2.47.0.338.g60cca15819-goog