[PATCH AUTOSEL 5.15 7/8] powerpc/mm: Fix UBSAN warning reported on hugetlb

Sasha Levin
2022-10-14T13:55:20Z

From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>

[ Upstream commit 7dd3a7b90bca2c12e2146a47d63cf69a2f5d7e89 ]

Powerpc architecture supports 16GB hugetlb pages with hash translation.
For 4K page size, this is implemented as a hugepage directory entry at
PGD level and for 64K it is implemented as a huge page pte at PUD level

With 16GB hugetlb size, offset within a page is greater than 32 bits.
Hence switch to use unsigned long type when using hugepd_shift.

In order to keep things simpler, we make sure we always use unsigned
long type when using hugepd_shift() even though all the hugetlb page
size won't require that.

The hugetlb_free_p*d_range changes are all related to nohash usage where
we can have multiple pgd entries pointing to the same hugepd entries.
Hence on book3s64 where we can have > 4GB hugetlb page size we will
always find more < next even if we compute the value of more correctly.

Hence there is no functional change in this patch except that it fixes
the below warning.

UBSAN: shift-out-of-bounds in arch/powerpc/mm/hugetlbpage.c:499:21
shift exponent 34 is too large for 32-bit type 'int'
CPU: 39 PID: 1673 Comm: a.out Not tainted 6.0.0-rc2-00327-gee88a56e8517-dirty #1
Call Trace:
dump_stack_lvl+0x98/0xe0 (unreliable)
ubsan_epilogue+0x18/0x70
__ubsan_handle_shift_out_of_bounds+0x1bc/0x390
hugetlb_free_pgd_range+0x5d8/0x600
free_pgtables+0x114/0x290
exit_mmap+0x150/0x550
mmput+0xcc/0x210
do_exit+0x420/0xdd0
do_group_exit+0x4c/0xd0
sys_exit_group+0x24/0x30
system_call_exception+0x250/0x600
system_call_common+0xec/0x250

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
[mpe: Drop generic change to be sent separately, change 1ULL to 1UL]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220908072440.258301-1-aneesh.kumar@linux.ibm.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/mm/hugetlbpage.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 9a75ba078e1b..d37dcd449e45 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -386,7 +386,7 @@ static void hugetlb_free_pmd_range(struct mmu_gather *tlb, pud_t *pud,
* single hugepage, but all of them point to
* the same kmem cache that holds the hugepte.
*/
- more = addr + (1 << hugepd_shift(*(hugepd_t *)pmd));
+ more = addr + (1UL << hugepd_shift(*(hugepd_t *)pmd));
if (more > next)
next = more;

@@ -428,7 +428,7 @@ static void hugetlb_free_pud_range(struct mmu_gather *tlb, p4d_t *p4d,
* single hugepage, but all of them point to
* the same kmem cache that holds the hugepte.
*/
- more = addr + (1 << hugepd_shift(*(hugepd_t *)pud));
+ more = addr + (1UL << hugepd_shift(*(hugepd_t *)pud));
if (more > next)
next = more;

@@ -490,7 +490,7 @@ void hugetlb_free_pgd_range(struct mmu_gather *tlb,
* for a single hugepage, but all of them point to the
* same kmem cache that holds the hugepte.
*/
- more = addr + (1 << hugepd_shift(*(hugepd_t *)pgd));
+ more = addr + (1UL << hugepd_shift(*(hugepd_t *)pgd));
if (more > next)
next = more;

--
2.35.1