[PATCH 5.15 49/83] hugetlb: check for undefined shift on 32 bit architectures

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Mike Kravetz <mike.kravetz@oracle.com>

commit ec4288fe63966b26d53907212ecd05dfa81dd2cc upstream.

Users can specify the hugetlb page size in the mmap, shmget and
memfd_create system calls.  This is done by using 6 bits within the flags
argument to encode the base-2 logarithm of the desired page size.  The
routine hstate_sizelog() uses the log2 value to find the corresponding
hugetlb hstate structure.  Converting the log2 value (page_size_log) to
potential hugetlb page size is the simple statement:

	1UL << page_size_log

Because only 6 bits are used for page_size_log, the left shift can not be
greater than 63.  This is fine on 64 bit architectures where a long is 64
bits.  However, if a value greater than 31 is passed on a 32 bit
architecture (where long is 32 bits) the shift will result in undefined
behavior.  This was generally not an issue as the result of the undefined
shift had to exactly match hugetlb page size to proceed.

Recent improvements in runtime checking have resulted in this undefined
behavior throwing errors such as reported below.

Fix by comparing page_size_log to BITS_PER_LONG before doing shift.

Link: https://lkml.kernel.org/r/20230216013542.138708-1-mike.kravetz@oracle.com
Link: https://lore.kernel.org/lkml/CA+G9fYuei_Tr-vN9GS7SfFyU1y9hNysnf=PB7kT0=yv4MiPgVg@mail.gmail.com/
Fixes: 42d7395feb56 ("mm: support more pagesizes for MAP_HUGETLB/SHM_HUGETLB")
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Reviewed-by: Jesper Juhl <jesperjuhl76@gmail.com>
Acked-by: Muchun Song <songmuchun@bytedance.com>
Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Cc: Anders Roxell <anders.roxell@linaro.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Sasha Levin <sashal@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 include/linux/hugetlb.h |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -684,7 +684,10 @@ static inline struct hstate *hstate_size
 	if (!page_size_log)
 		return &default_hstate;
 
-	return size_to_hstate(1UL << page_size_log);
+	if (page_size_log < BITS_PER_LONG)
+		return size_to_hstate(1UL << page_size_log);
+
+	return NULL;
 }
 
 static inline struct hstate *hstate_vma(struct vm_area_struct *vma)