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

From: Yang Shi
Date: Fri Oct 04 2024 - 12:37:30 EST




On 10/4/24 9:29 AM, Yang Shi wrote:


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.

The size parameter passed to dmam_alloc_coherent() is size_t type. We may do:

+#define SIZE_4G (4 * 1024 * 1024 * 1024ULL)
+
 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;
+       u64 num_sids;

        /* It is not practical to have too large stream id size for linear */
        if (smmu->sid_bits > 31)
@@ -3667,6 +3669,9 @@ static int arm_smmu_init_strtab_linear(struct arm_smmu_device *smmu)
        num_sids = arm_smmu_strtab_num_sids(smmu);

        size = num_sids * sizeof(struct arm_smmu_ste);
+       if (size > SIZE_4G)
+               return -EINVAL;
+
        cfg->linear.table = dmam_alloc_coherent(smmu->dev, size,
&cfg->linear.ste_dma,
                                                GFP_KERNEL);



Jason