[PATCH] powerpc/mm: Fix UBSAN warning reported on hugetlb

[Christophe Leroy]

Le 08/09/2022 à 09:24, Aneesh Kumar K.V a écrit :
> 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.
> 
> Inorder 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 walk_hugepd_range change won't have any impact because we don't use that for
> the hugetlb walk. That code is needed to support hugepd on init_mm with PPC_8XX
> and 8M page. Even though 8M page size won't result in any real issue, we update
> that to keep it simpler.
> 
> 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:
>   [c00000002ccb3720] [c000000000cb21e4] dump_stack_lvl+0x98/0xe0 (unreliable)
>   [c00000002ccb3760] [c000000000cacf60] ubsan_epilogue+0x18/0x70
>   [c00000002ccb37c0] [c000000000cac44c] __ubsan_handle_shift_out_of_bounds+0x1bc/0x390
>   [c00000002ccb38c0] [c0000000000d6f78] hugetlb_free_pgd_range+0x5d8/0x600
>   [c00000002ccb39f0] [c000000000550e94] free_pgtables+0x114/0x290
>   [c00000002ccb3ac0] [c00000000056cbe0] exit_mmap+0x150/0x550
>   [c00000002ccb3be0] [c00000000017bf0c] mmput+0xcc/0x210
>   [c00000002ccb3c20] [c00000000018f180] do_exit+0x420/0xdd0
>   [c00000002ccb3cf0] [c00000000018fcdc] do_group_exit+0x4c/0xd0
>   [c00000002ccb3d30] [c00000000018fd84] sys_exit_group+0x24/0x30
>   [c00000002ccb3d50] [c00000000003cde0] system_call_exception+0x250/0x600
>   [c00000002ccb3e10] [c00000000000c3bc] system_call_common+0xec/0x250
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
> ---
>   arch/powerpc/mm/hugetlbpage.c | 6 +++---
>   mm/pagewalk.c                 | 2 +-
>   2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> index fa7a3d21a751..e210b737658c 100644
> --- a/mm/pagewalk.c
> +++ b/mm/pagewalk.c
> @@ -65,7 +65,7 @@ static int walk_hugepd_range(hugepd_t *phpd, unsigned long addr,
>   	int err = 0;
>   	const struct mm_walk_ops *ops = walk->ops;
>   	int shift = hugepd_shift(*phpd);
> -	int page_size = 1 << shift;
> +	long page_size = 1UL << shift;

1UL means _unsigned_ long. Should page_size be unsigned ?

>   
>   	if (!ops->pte_entry)
>   		return 0;