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RDMA/ucontext: Fix regression with disassociate

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When this code was consolidated the intention was that the VMA would
become backed by anonymous zero pages after the zap_vma_pte - however this
very subtly relied on setting the vm_ops = NULL and clearing the VM_SHARED
bits to transform the VMA into an anonymous VMA. Since the vm_ops was
removed this broke.

Now userspace gets a SIGBUS if it touches the vma after disassociation.

Instead of converting the VMA to anonymous provide a fault handler that
puts a zero'd page into the VMA when user-space touches it after
disassociation.

Cc: stable@vger.kernel.org
Suggested-by: Andrea Arcangeli <aarcange@redhat.com>
Fixes: 5f9794dc94 ("RDMA/ucontext: Add a core API for mmaping driver IO memory")
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
This commit is contained in:
Jason Gunthorpe 2019-04-16 14:07:28 +03:00
parent d5e560d3f7
commit 67f269b37f
2 changed files with 50 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
drivers/infiniband/core/uverbs.h
View File

@ -160,6 +160,7 @@ struct ib_uverbs_file {
struct mutex umap_lock;
struct list_head umaps;
struct page *disassociate_page;
struct idr idr;
/* spinlock protects write access to idr */

52
drivers/infiniband/core/uverbs_main.c
View File

@ -208,6 +208,9 @@ void ib_uverbs_release_file(struct kref *ref)
kref_put(&file->async_file->ref,
ib_uverbs_release_async_event_file);
put_device(&file->device->dev);
if (file->disassociate_page)
__free_pages(file->disassociate_page, 0);
kfree(file);
}
@ -877,9 +880,50 @@ static void rdma_umap_close(struct vm_area_struct *vma)
kfree(priv);
}
/*
* Once the zap_vma_ptes has been called touches to the VMA will come here and
* we return a dummy writable zero page for all the pfns.
*/
static vm_fault_t rdma_umap_fault(struct vm_fault *vmf)
{
struct ib_uverbs_file *ufile = vmf->vma->vm_file->private_data;
struct rdma_umap_priv *priv = vmf->vma->vm_private_data;
vm_fault_t ret = 0;
if (!priv)
return VM_FAULT_SIGBUS;
/* Read only pages can just use the system zero page. */
if (!(vmf->vma->vm_flags & (VM_WRITE | VM_MAYWRITE))) {
vmf->page = ZERO_PAGE(vmf->vm_start);
get_page(vmf->page);
return 0;
}
mutex_lock(&ufile->umap_lock);
if (!ufile->disassociate_page)
ufile->disassociate_page =
alloc_pages(vmf->gfp_mask | __GFP_ZERO, 0);
if (ufile->disassociate_page) {
/*
* This VMA is forced to always be shared so this doesn't have
* to worry about COW.
*/
vmf->page = ufile->disassociate_page;
get_page(vmf->page);
} else {
ret = VM_FAULT_SIGBUS;
}
mutex_unlock(&ufile->umap_lock);
return ret;
}
static const struct vm_operations_struct rdma_umap_ops = {
.open = rdma_umap_open,
.close = rdma_umap_close,
.fault = rdma_umap_fault,
};
static struct rdma_umap_priv *rdma_user_mmap_pre(struct ib_ucontext *ucontext,
@ -889,6 +933,9 @@ static struct rdma_umap_priv *rdma_user_mmap_pre(struct ib_ucontext *ucontext,
struct ib_uverbs_file *ufile = ucontext->ufile;
struct rdma_umap_priv *priv;
if (!(vma->vm_flags & VM_SHARED))
return ERR_PTR(-EINVAL);
if (vma->vm_end - vma->vm_start != size)
return ERR_PTR(-EINVAL);
@ -992,7 +1039,7 @@ void uverbs_user_mmap_disassociate(struct ib_uverbs_file *ufile)
* at a time to get the lock ordering right. Typically there
* will only be one mm, so no big deal.
*/
down_write(&mm->mmap_sem);
down_read(&mm->mmap_sem);
mutex_lock(&ufile->umap_lock);
list_for_each_entry_safe (priv, next_priv, &ufile->umaps,
list) {
@ -1004,10 +1051,9 @@ void uverbs_user_mmap_disassociate(struct ib_uverbs_file *ufile)
zap_vma_ptes(vma, vma->vm_start,
vma->vm_end - vma->vm_start);
vma->vm_flags &= ~(VM_SHARED | VM_MAYSHARE);
}
mutex_unlock(&ufile->umap_lock);
up_write(&mm->mmap_sem);
up_read(&mm->mmap_sem);
mmput(mm);
}
}