Re: [PATCH v4] tee: Use iov_iter to better support shared buffer registration

[Sumit Garg]

On Thu, 30 Nov 2023 at 14:38, Arnaud POULIQUEN
<arnaud.pouliquen@xxxxxxxxxxx> wrote:
>
>
>
> On 11/30/23 08:54, Sumit Garg wrote:
> > On Wed, 29 Nov 2023 at 22:15, Arnaud Pouliquen
> > <arnaud.pouliquen@xxxxxxxxxxx> wrote:
> >>
> >> Currently it's not possible to register kernel buffers with TEE
> >> which are allocated via vmalloc.
> >>
> >> Use iov_iter and associated helper functions to manage the page
> >> registration for all type of memories.
> >>
> >> Suggested-by: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> >> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@xxxxxxxxxxx>
> >> ---
> >> Update from V3 to V4:
> >> - improve commit message,
> >> - use import_ubuf() instead of iov_iter_init(),
> >> - move shm_get_kernel_pages in register_shm_helper,
> >> - put back untagged_addr in register_shm_helper(),
> >> - move the comment related to pin pages from shm_get_kernel_pages()
> >>   to register_shm_helper().
> >>
> >> Update from V2 to V3:
> >> - break lines longer than 80 columns.
> >>
> >> Update from V1 to V2:
> >> - replace ITER_SOURCE by ITER_DEST flag in tee_shm_register_user_buf(),
> >> - replace IS_ERR_OR NULL(shm) by IS_ERR(shm) in tee_shm_register_user_buf().
> >>
> >> V1:
> >> The support of buffer registration allocated with vmalloc is no more
> >> available since c83900393aa1 ("tee: Remove vmalloc page support").
> >>
> >> This patch is an alternative to a revert and resulted from a discussion
> >> with Christopher Hellwig [1].
> >>
> >> This patch has been tested using xtest tool in optee qemu environment [2]
> >> and using the series related to the remoteproc tee that should be
> >> proposed soon [3].
> >>
> >> References:
> >> [1] https://lore.kernel.org/linux-arm-kernel/18a8528d-7d9d-6ed0-0045-5ee47dd39fb2@xxxxxxxxxxx/T/#m8ec683c44fcd9b69c2aee42eaed0793afac9dd18in
> >> [2] https://optee.readthedocs.io/en/latest/building/devices/qemu.html#build-instructions
> >> [3] https://lore.kernel.org/linux-arm-kernel/18a8528d-7d9d-6ed0-0045-5ee47dd39fb2@xxxxxxxxxxx/T/#maca0a1fc897aadd54c7deac432e11473fe970d1d
> >> ---
> >>  drivers/tee/tee_shm.c | 83 ++++++++++++++++++++++++-------------------
> >>  1 file changed, 46 insertions(+), 37 deletions(-)
> >>
> >> diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
> >> index 673cf0359494..ac73e8143233 100644
> >> --- a/drivers/tee/tee_shm.c
> >> +++ b/drivers/tee/tee_shm.c
> >> @@ -22,23 +22,12 @@ static void shm_put_kernel_pages(struct page **pages, size_t page_count)
> >>                 put_page(pages[n]);
> >>  }
> >>
> >> -static int shm_get_kernel_pages(unsigned long start, size_t page_count,
> >> -                               struct page **pages)
> >> +static void shm_get_kernel_pages(struct page **pages, size_t page_count)
> >>  {
> >> -       struct page *page;
> >>         size_t n;
> >>
> >> -       if (WARN_ON_ONCE(is_vmalloc_addr((void *)start) ||
> >> -                        is_kmap_addr((void *)start)))
> >> -               return -EINVAL;
> >> -
> >> -       page = virt_to_page((void *)start);
> >> -       for (n = 0; n < page_count; n++) {
> >> -               pages[n] = page + n;
> >> +       for (n = 0; n < page_count; n++)
> >>                 get_page(pages[n]);
> >> -       }
> >> -
> >> -       return page_count;
> >>  }
> >>
> >>  static void release_registered_pages(struct tee_shm *shm)
> >> @@ -214,13 +203,14 @@ struct tee_shm *tee_shm_alloc_priv_buf(struct tee_context *ctx, size_t size)
> >>  EXPORT_SYMBOL_GPL(tee_shm_alloc_priv_buf);
> >>
> >>  static struct tee_shm *
> >> -register_shm_helper(struct tee_context *ctx, unsigned long addr,
> >> -                   size_t length, u32 flags, int id)
> >> +register_shm_helper(struct tee_context *ctx, struct iov_iter *iter, u32 flags,
> >> +                   int id)
> >>  {
> >>         struct tee_device *teedev = ctx->teedev;
> >>         struct tee_shm *shm;
> >> -       unsigned long start;
> >> -       size_t num_pages;
> >> +       unsigned long start, addr;
> >> +       size_t num_pages, off;
> >> +       ssize_t len;
> >>         void *ret;
> >>         int rc;
> >>
> >> @@ -245,31 +235,38 @@ register_shm_helper(struct tee_context *ctx, unsigned long addr,
> >>         shm->flags = flags;
> >>         shm->ctx = ctx;
> >>         shm->id = id;
> >> -       addr = untagged_addr(addr);
> >> +       addr = untagged_addr((unsigned long)iter_iov_addr(iter));
> >>         start = rounddown(addr, PAGE_SIZE);
> >> -       shm->offset = addr - start;
> >> -       shm->size = length;
> >> -       num_pages = (roundup(addr + length, PAGE_SIZE) - start) / PAGE_SIZE;
> >> +       num_pages = iov_iter_npages(iter, INT_MAX);
> >> +       if (!num_pages) {
> >> +               ret = ERR_PTR(-ENOMEM);
> >> +               goto err_ctx_put;
> >> +       }
> >> +
> >>         shm->pages = kcalloc(num_pages, sizeof(*shm->pages), GFP_KERNEL);
> >>         if (!shm->pages) {
> >>                 ret = ERR_PTR(-ENOMEM);
> >>                 goto err_free_shm;
> >>         }
> >>
> >> -       if (flags & TEE_SHM_USER_MAPPED)
> >> -               rc = pin_user_pages_fast(start, num_pages, FOLL_WRITE,
> >> -                                        shm->pages);
> >> -       else
> >> -               rc = shm_get_kernel_pages(start, num_pages, shm->pages);
> >> -       if (rc > 0)
> >> -               shm->num_pages = rc;
> >> -       if (rc != num_pages) {
> >> -               if (rc >= 0)
> >> -                       rc = -ENOMEM;
> >> -               ret = ERR_PTR(rc);
> >> -               goto err_put_shm_pages;
> >> +       len = iov_iter_extract_pages(iter, &shm->pages, LONG_MAX, num_pages, 0,
> >> +                                    &off);
> >> +       if (unlikely(len <= 0)) {
> >> +               ret = len ? ERR_PTR(len) : ERR_PTR(-ENOMEM);
> >> +               goto err_free_shm_pages;
> >>         }
> >>
> >> +       /*
> >> +        * iov_iter_extract_kvec_pages does not get reference on the pages,
> >> +        * get a pin on them.
> >
> > I think you meant: "get a reference on them". But I don't see the
> > value of this comment since iov_iter_extract_kvec_pages() already has
> > been commented properly as follows:
> >
> > /*
> >  * Extract a list of virtually contiguous pages from an ITER_KVEC iterator.
> >  * This does not get references on the pages, nor does it get a pin on them.
> >  */
> >
>
> I spent some time debugging this part. Since we use the same API for both user
> and kernel buffers, we wouldn't expect to have any specific actions to take.
> Therefore, I thought it would be helpful to add a comment explaining the reason
> for this specific code, rather than go deeper into iov_iter to understand it.
>

Fair enough, let's keep it with s/pin/reference/.

> But if you don't see the value, I can remove the comment.
>
> >> +        */
> >> +       if (iov_iter_is_kvec(iter))
> >> +               shm_get_kernel_pages(shm->pages, num_pages);
> >> +
> >> +       shm->offset = off;
> >> +       shm->size = len;
> >> +       shm->num_pages = num_pages;
> >> +
> >>         rc = teedev->desc->ops->shm_register(ctx, shm, shm->pages,
> >>                                              shm->num_pages, start);
> >>         if (rc) {
> >> @@ -279,10 +276,11 @@ register_shm_helper(struct tee_context *ctx, unsigned long addr,
> >>
> >>         return shm;
> >>  err_put_shm_pages:
> >> -       if (flags & TEE_SHM_USER_MAPPED)
> >> +       if (!iov_iter_is_kvec(iter))
> >>                 unpin_user_pages(shm->pages, shm->num_pages);
> >>         else
> >>                 shm_put_kernel_pages(shm->pages, shm->num_pages);
> >> +err_free_shm_pages:
> >>         kfree(shm->pages);
> >>  err_free_shm:
> >>         kfree(shm);
> >> @@ -307,8 +305,9 @@ struct tee_shm *tee_shm_register_user_buf(struct tee_context *ctx,
> >>         u32 flags = TEE_SHM_USER_MAPPED | TEE_SHM_DYNAMIC;
> >>         struct tee_device *teedev = ctx->teedev;
> >>         struct tee_shm *shm;
> >> +       struct iov_iter iter;
> >>         void *ret;
> >> -       int id;
> >> +       int id, err;
> >>
> >>         if (!access_ok((void __user *)addr, length))
> >>                 return ERR_PTR(-EFAULT);
> >> @@ -319,7 +318,11 @@ struct tee_shm *tee_shm_register_user_buf(struct tee_context *ctx,
> >>         if (id < 0)
> >>                 return ERR_PTR(id);
> >>
> >> -       shm = register_shm_helper(ctx, addr, length, flags, id);
> >> +       err = import_ubuf(ITER_DEST, (void __user *)addr, length, &iter);
> >
> > As I mentioned in a previous review, import_ubuf() already does the
> > access_ok() check, so we don't need the extra access_ok() check above.
> > Also, you should move import_ubuf() to be the first invocation within
> > this API.
>
> My apologies, I re-added import_ubuf() during testing to debug an issue and

I suppose you intended to mention access_ok() here, BTW, no worries :).

-Sumit

> forgot to
> remove it afterwards.
>
> Thanks and regards,
> Arnaud
>
> >
> > -Sumit
> >
> >> +       if (err)
> >> +               return ERR_PTR(err);
> >> +
> >> +       shm = register_shm_helper(ctx, &iter, flags, id);
> >>         if (IS_ERR(shm)) {
> >>                 mutex_lock(&teedev->mutex);
> >>                 idr_remove(&teedev->idr, id);
> >> @@ -352,8 +355,14 @@ struct tee_shm *tee_shm_register_kernel_buf(struct tee_context *ctx,
> >>                                             void *addr, size_t length)
> >>  {
> >>         u32 flags = TEE_SHM_DYNAMIC;
> >> +       struct kvec kvec;
> >> +       struct iov_iter iter;
> >> +
> >> +       kvec.iov_base = addr;
> >> +       kvec.iov_len = length;
> >> +       iov_iter_kvec(&iter, ITER_DEST, &kvec, 1, length);
> >>
> >> -       return register_shm_helper(ctx, (unsigned long)addr, length, flags, -1);
> >> +       return register_shm_helper(ctx, &iter, flags, -1);
> >>  }
> >>  EXPORT_SYMBOL_GPL(tee_shm_register_kernel_buf);
> >>
> >> --
> >> 2.25.1
> >>