Re: [PATCH 3/4] binder: Add flags to relinquish ownership of fds

[T.J. Mercier]

On Fri, Jan 20, 2023 at 1:25 PM Carlos Llamas <cmllamas@xxxxxxxxxx> wrote:
>
> On Mon, Jan 09, 2023 at 09:38:06PM +0000, T.J. Mercier wrote:
> > From: Hridya Valsaraju <hridya@xxxxxxxxxx>
> >
> > This patch introduces flags BINDER_FD_FLAG_XFER_CHARGE, and
> > BINDER_FD_FLAG_XFER_CHARGE that a process sending an individual fd or
>
> I believe the second one was meant to be BINDER_FDA_FLAG_XFER_CHARGE.
> However, I don't think a separation of flags is needed. We process each
> fd in the array individually anyway. So, it's OK to reuse the FD flags
> for FDAs too.

Yes, thanks.
>
>
> > fd array to another process over binder IPC can set to relinquish
> > ownership of the fd(s) being sent for memory accounting purposes. If the
> > flag is found to be set during the fd or fd array translation and the
> > fd is for a DMA-BUF, the buffer is uncharged from the sender's cgroup
> > and charged to the receiving process's cgroup instead.
> >
> > It is up to the sending process to ensure that it closes the fds
> > regardless of whether the transfer failed or succeeded.
> >
> > Most graphics shared memory allocations in Android are done by the
> > graphics allocator HAL process. On requests from clients, the HAL
> > process allocates memory and sends the fds to the clients over binder
> > IPC. The graphics allocator HAL will not retain any references to the
> > buffers. When the HAL sets *_FLAG_XFER_CHARGE for fd arrays holding
> > DMA-BUF fds, or individual fd objects, binder will transfer the charge
> > for the buffer from the allocator process cgroup to the client process
> > cgroup.
> >
> > The pad [1] and pad_flags [2] fields of binder_fd_object and
> > binder_fda_array_object come from alignment with flat_binder_object and
> > have never been exposed for use from userspace. This new flags use
> > follows the pattern set by binder_buffer_object.
> >
> > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/include/uapi/linux/android/binder.h?id=feba3900cabb8e7c87368faa28e7a6936809ba22
> > [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/include/uapi/linux/android/binder.h?id=5cdcf4c6a638591ec0e98c57404a19e7f9997567
> >
> > Signed-off-by: Hridya Valsaraju <hridya@xxxxxxxxxx>
> > Signed-off-by: T.J. Mercier <tjmercier@xxxxxxxxxx>
> > ---
> >  Documentation/admin-guide/cgroup-v2.rst |  3 ++-
> >  drivers/android/binder.c                | 31 +++++++++++++++++++++----
> >  drivers/dma-buf/dma-buf.c               |  4 +---
> >  include/linux/dma-buf.h                 |  1 +
> >  include/uapi/linux/android/binder.h     | 23 ++++++++++++++----
> >  5 files changed, 50 insertions(+), 12 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> > index 538ae22bc514..d225295932c0 100644
> > --- a/Documentation/admin-guide/cgroup-v2.rst
> > +++ b/Documentation/admin-guide/cgroup-v2.rst
> > @@ -1457,7 +1457,8 @@ PAGE_SIZE multiple when read back.
> >
> >         dmabuf (npn)
> >               Amount of memory used for exported DMA buffers allocated by the cgroup.
> > -             Stays with the allocating cgroup regardless of how the buffer is shared.
> > +             Stays with the allocating cgroup regardless of how the buffer is shared
> > +             unless explicitly transferred.
> >
> >         workingset_refault_anon
> >               Number of refaults of previously evicted anonymous pages.
> > diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> > index 880224ec6abb..9830848c8d25 100644
> > --- a/drivers/android/binder.c
> > +++ b/drivers/android/binder.c
> > @@ -42,6 +42,7 @@
> >
> >  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> >
> > +#include <linux/dma-buf.h>
> >  #include <linux/fdtable.h>
> >  #include <linux/file.h>
> >  #include <linux/freezer.h>
> > @@ -2237,7 +2238,7 @@ static int binder_translate_handle(struct flat_binder_object *fp,
> >       return ret;
> >  }
> >
> > -static int binder_translate_fd(u32 fd, binder_size_t fd_offset,
> > +static int binder_translate_fd(u32 fd, binder_size_t fd_offset, __u32 flags,
> >                              struct binder_transaction *t,
> >                              struct binder_thread *thread,
> >                              struct binder_transaction *in_reply_to)
> > @@ -2275,6 +2276,26 @@ static int binder_translate_fd(u32 fd, binder_size_t fd_offset,
> >               goto err_security;
> >       }
> >
> > +     if (IS_ENABLED(CONFIG_MEMCG) && (flags & BINDER_FD_FLAG_XFER_CHARGE)) {
> > +             struct dma_buf *dmabuf;
> > +
> > +             if (unlikely(!is_dma_buf_file(file))) {
> > +                     binder_user_error(
> > +                             "%d:%d got transaction with XFER_CHARGE for non-dmabuf fd, %d\n",
> > +                             proc->pid, thread->pid, fd);
> > +                     ret = -EINVAL;
> > +                     goto err_dmabuf;
> > +             }
> > +
> > +             dmabuf = file->private_data;
> > +             ret = dma_buf_transfer_charge(dmabuf, target_proc->tsk);
> > +             if (ret) {
> > +                     pr_warn("%d:%d Unable to transfer DMA-BUF fd charge to %d\n",
> > +                             proc->pid, thread->pid, target_proc->pid);
> > +                     goto err_xfer;
> > +             }
> > +     }
> > +
> >       /*
> >        * Add fixup record for this transaction. The allocation
> >        * of the fd in the target needs to be done from a
> > @@ -2294,6 +2315,8 @@ static int binder_translate_fd(u32 fd, binder_size_t fd_offset,
> >       return ret;
> >
> >  err_alloc:
> > +err_xfer:
> > +err_dmabuf:
> >  err_security:
> >       fput(file);
> >  err_fget:
> > @@ -2604,7 +2627,7 @@ static int binder_translate_fd_array(struct list_head *pf_head,
> >
> >               ret = copy_from_user(&fd, sender_ufda_base + sender_uoffset, sizeof(fd));
> >               if (!ret)
> > -                     ret = binder_translate_fd(fd, offset, t, thread,
> > +                     ret = binder_translate_fd(fd, offset, fda->flags, t, thread,
> >                                                 in_reply_to);
> >               if (ret)
> >                       return ret > 0 ? -EINVAL : ret;
> > @@ -3383,8 +3406,8 @@ static void binder_transaction(struct binder_proc *proc,
> >                       struct binder_fd_object *fp = to_binder_fd_object(hdr);
> >                       binder_size_t fd_offset = object_offset +
> >                               (uintptr_t)&fp->fd - (uintptr_t)fp;
> > -                     int ret = binder_translate_fd(fp->fd, fd_offset, t,
> > -                                                   thread, in_reply_to);
> > +                     int ret = binder_translate_fd(fp->fd, fd_offset, fp->flags,
> > +                                                   t, thread, in_reply_to);
> >
> >                       fp->pad_binder = 0;
> >                       if (ret < 0 ||
>
> IMO the changes to the dma-buf api should some in a separate patch. So
> those can be approved and managed separately.
>
I've actually already dropped these based on feedback from Hillf, so
there are no longer any dma-buf.c changes on this patch for the v2 I
have queued up.

> > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> > index fd6c5002032b..a65b42433099 100644
> > --- a/drivers/dma-buf/dma-buf.c
> > +++ b/drivers/dma-buf/dma-buf.c
> > @@ -34,8 +34,6 @@
> >
> >  #include "dma-buf-sysfs-stats.h"
> >
> > -static inline int is_dma_buf_file(struct file *);
> > -
> >  struct dma_buf_list {
> >       struct list_head head;
> >       struct mutex lock;
> > @@ -527,7 +525,7 @@ static const struct file_operations dma_buf_fops = {
> >  /*
> >   * is_dma_buf_file - Check if struct file* is associated with dma_buf
> >   */
> > -static inline int is_dma_buf_file(struct file *file)
> > +int is_dma_buf_file(struct file *file)
> >  {
> >       return file->f_op == &dma_buf_fops;
> >  }
> > diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> > index 6aa128d76aa7..092d572ce528 100644
> > --- a/include/linux/dma-buf.h
> > +++ b/include/linux/dma-buf.h
> > @@ -595,6 +595,7 @@ dma_buf_attachment_is_dynamic(struct dma_buf_attachment *attach)
> >       return !!attach->importer_ops;
> >  }
> >
> > +int is_dma_buf_file(struct file *file);
> >  struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
> >                                         struct device *dev);
> >  struct dma_buf_attachment *
> > diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h
> > index e72e4de8f452..696c2bdb8a7e 100644
> > --- a/include/uapi/linux/android/binder.h
> > +++ b/include/uapi/linux/android/binder.h
> > @@ -91,14 +91,14 @@ struct flat_binder_object {
> >  /**
> >   * struct binder_fd_object - describes a filedescriptor to be fixed up.
> >   * @hdr:     common header structure
> > - * @pad_flags:       padding to remain compatible with old userspace code
> > + * @flags:   One or more BINDER_FD_FLAG_* flags
> >   * @pad_binder:      padding to remain compatible with old userspace code
> >   * @fd:              file descriptor
> >   * @cookie:  opaque data, used by user-space
> >   */
> >  struct binder_fd_object {
> >       struct binder_object_header     hdr;
> > -     __u32                           pad_flags;
> > +     __u32                           flags;
> >       union {
> >               binder_uintptr_t        pad_binder;
> >               __u32                   fd;
> > @@ -107,6 +107,17 @@ struct binder_fd_object {
> >       binder_uintptr_t                cookie;
> >  };
> >
> > +enum {
> > +     /**
> > +      * @BINDER_FD_FLAG_XFER_CHARGE
> > +      *
> > +      * When set, the sender of a binder_fd_object wishes to relinquish ownership of the fd for
> > +      * memory accounting purposes. If the fd is for a DMA-BUF, the buffer is uncharged from the
> > +      * sender's cgroup and charged to the receiving process's cgroup instead.
> > +      */
> > +     BINDER_FD_FLAG_XFER_CHARGE = 0x01,
> > +};
> > +
> >  /* struct binder_buffer_object - object describing a userspace buffer
> >   * @hdr:             common header structure
> >   * @flags:           one or more BINDER_BUFFER_* flags
> > @@ -141,7 +152,7 @@ enum {
> >
> >  /* struct binder_fd_array_object - object describing an array of fds in a buffer
> >   * @hdr:             common header structure
> > - * @pad:             padding to ensure correct alignment
> > + * @flags:           One or more BINDER_FDA_FLAG_* flags
> >   * @num_fds:         number of file descriptors in the buffer
> >   * @parent:          index in offset array to buffer holding the fd array
> >   * @parent_offset:   start offset of fd array in the buffer
> > @@ -162,12 +173,16 @@ enum {
> >   */
> >  struct binder_fd_array_object {
> >       struct binder_object_header     hdr;
> > -     __u32                           pad;
> > +     __u32                           flags;
> >       binder_size_t                   num_fds;
> >       binder_size_t                   parent;
> >       binder_size_t                   parent_offset;
> >  };
> >
> > +enum {
> > +     BINDER_FDA_FLAG_XFER_CHARGE = BINDER_FD_FLAG_XFER_CHARGE,
> > +};
> > +
>
> I would prefer to drop this. It should avoid silly mistakes in
> userspace similar to the typo in the commit message above.
>
Ok I'll make that work.
>
> >  /*
> >   * On 64-bit platforms where user code may run in 32-bits the driver must
> >   * translate the buffer (and local binder) addresses appropriately.
> > --
> > 2.39.0.314.g84b9a713c41-goog
> >
>
> Thanks,
> --
> Carlos Llamas