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Message-ID: <20251009055401.94174-1-ioworker0@gmail.com>
Date: Thu, 9 Oct 2025 13:54:01 +0800
From: Lance Yang <ioworker0@...il.com>
To: akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org,
linux-mm@...ck.org,
urezki@...il.com,
yadong.qi@...ux.alibaba.com,
ying.huang@...ux.alibaba.com
Subject: Re: [PATCH] mm: vmalloc: BUG_ON if mapping size is not PAGE_SIZE aligned
>> In mm/vmalloc.c, the function vmap_pte_range() assumes that the
>> mapping size is aligned to PAGE_SIZE. If this assumption is
>> violated, the loop will become infinite because the termination
>> condition (`addr != end`) will never be met. This can lead to
>> overwriting other VA ranges and/or random pages physically follow
>> the page table.
>>
>> It's the caller's responsibility to ensure that the mapping size
>> is aligned to PAGE_SIZE. However, the memory corruption is hard
>> to root cause. To identify the programming error in the caller
>> easier, check whether the mapping size is PAGE_SIZE aligned with
>> BUG_ON().
>>
>> ..
>>
>> --- a/mm/vmalloc.c
>> +++ b/mm/vmalloc.c
>> @@ -100,6 +100,8 @@ static int vmap_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
>> struct page *page;
>> unsigned long size = PAGE_SIZE;
>>
>> + BUG_ON(!PAGE_ALIGNED(end - addr));
>> +
>> pfn = phys_addr >> PAGE_SHIFT;
>> pte = pte_alloc_kernel_track(pmd, addr, mask);
>> if (!pte)
>
>We try to avoid adding BUG()s - deliberately crashing the kernel is
>pretty cruel to the user. It's far better to WARN and to continue in
>some fashion so the user can at least gather logs, etc.
>
>How about
>
> if (WARN_ON(!PAGE_ALIGNED(end - addr)))
> return -ENOMEM;
>
>?
>
>(Or VM_WARN_ON)
I agree with Andrew. Using WARN_ON/VM_WARN_ON and returning an error is
the way to go.
AFAIK, we are moving away from BUG_ON() in MM whenever an error can be
handled gracefully.
Cheers,
Lance
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