linux-kernel - Re: [v2 PATCH] iommu/arm-smmu-v3: Fix L1 stream table index calculation for 32-bit sid size

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Message-ID: <7ad66e5f-d6f8-4144-8ab2-d4ea499e2665@os.amperecomputing.com>
Date: Fri, 4 Oct 2024 09:29:33 -0700
From: Yang Shi <yang@...amperecomputing.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Nicolin Chen <nicolinc@...dia.com>, james.morse@....com, will@...nel.org,
 robin.murphy@....com, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [v2 PATCH] iommu/arm-smmu-v3: Fix L1 stream table index
 calculation for 32-bit sid size



On 10/4/24 9:14 AM, Jason Gunthorpe wrote:
> On Fri, Oct 04, 2024 at 09:05:46AM -0700, Yang Shi wrote:
>>
>> On 10/4/24 5:43 AM, Jason Gunthorpe wrote:
>>> On Thu, Oct 03, 2024 at 08:31:23AM -0700, Yang Shi wrote:
>>>> If I understand correctly, the check is mainly used to avoid the u64 -> u32
>>>> overflow. This check guarantee no overflow. If some crazy hardware really
>>>> requests that large memory, the allocation will fail.
>>> Sure, the kalloc will print a warn on anyhow if it is too big
>> Thank you. Will spin a new revision.
> Oh wait a sec, it is not so simple, the 31 is too big because the
> multiply will overflow or truncate to size_t too. This is why I picked
> something lower.

How about define the size as u64?

  static int arm_smmu_init_strtab_linear(struct arm_smmu_device *smmu)
  {
-       u32 size;
+       u64 size;
         struct arm_smmu_strtab_cfg *cfg = &smmu->strtab_cfg;
         u32 num_sids;

It won't overflow and the large allocation will fail anyway.

>
> Jason