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    Subject[PATCH 5.15 488/667] iommu/arm-smmu-v3-sva: Fix mm use-after-free
    Date
    From: Jean-Philippe Brucker <jean-philippe@linaro.org>

    [ Upstream commit cbd23144f7662b00bcde32a938c4a4057e476d68 ]

    We currently call arm64_mm_context_put() without holding a reference to
    the mm, which can result in use-after-free. Call mmgrab()/mmdrop() to
    ensure the mm only gets freed after we unpinned the ASID.

    Fixes: 32784a9562fb ("iommu/arm-smmu-v3: Implement iommu_sva_bind/unbind()")
    Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
    Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org>
    Link: https://lore.kernel.org/r/20220426130444.300556-1-jean-philippe@linaro.org
    Signed-off-by: Will Deacon <will@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c | 13 +++++++++++--
    1 file changed, 11 insertions(+), 2 deletions(-)

    diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
    index f763c1430d15..e2e80eb2840c 100644
    --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
    +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
    @@ -6,6 +6,7 @@
    #include <linux/mm.h>
    #include <linux/mmu_context.h>
    #include <linux/mmu_notifier.h>
    +#include <linux/sched/mm.h>
    #include <linux/slab.h>

    #include "arm-smmu-v3.h"
    @@ -96,9 +97,14 @@ static struct arm_smmu_ctx_desc *arm_smmu_alloc_shared_cd(struct mm_struct *mm)
    struct arm_smmu_ctx_desc *cd;
    struct arm_smmu_ctx_desc *ret = NULL;

    + /* Don't free the mm until we release the ASID */
    + mmgrab(mm);
    +
    asid = arm64_mm_context_get(mm);
    - if (!asid)
    - return ERR_PTR(-ESRCH);
    + if (!asid) {
    + err = -ESRCH;
    + goto out_drop_mm;
    + }

    cd = kzalloc(sizeof(*cd), GFP_KERNEL);
    if (!cd) {
    @@ -165,6 +171,8 @@ static struct arm_smmu_ctx_desc *arm_smmu_alloc_shared_cd(struct mm_struct *mm)
    kfree(cd);
    out_put_context:
    arm64_mm_context_put(mm);
    +out_drop_mm:
    + mmdrop(mm);
    return err < 0 ? ERR_PTR(err) : ret;
    }

    @@ -173,6 +181,7 @@ static void arm_smmu_free_shared_cd(struct arm_smmu_ctx_desc *cd)
    if (arm_smmu_free_asid(cd)) {
    /* Unpin ASID */
    arm64_mm_context_put(cd->mm);
    + mmdrop(cd->mm);
    kfree(cd);
    }
    }
    --
    2.35.1


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