[PATCH v2 3/4] binder: Add flags to relinquish ownership of fds
Carlos Llamas
cmllamas at google.com
Wed Jan 25 17:30:15 UTC 2023
On Mon, Jan 23, 2023 at 07:17:25PM +0000, T.J. Mercier wrote:
> From: Hridya Valsaraju <hridya at google.com>
>
> This patch introduces flag BINDER_FD_FLAG_XFER_CHARGE that a process
> sending an individual fd or 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 BINDER_FD_FLAG_XFER_CHARGE, 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 at google.com>
> Signed-off-by: T.J. Mercier <tjmercier at google.com>
> ---
> Documentation/admin-guide/cgroup-v2.rst | 3 ++-
> drivers/android/binder.c | 25 +++++++++++++++++++++----
> include/uapi/linux/android/binder.h | 19 +++++++++++++++----
> 3 files changed, 38 insertions(+), 9 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..5e707974793f 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 +2276,20 @@ 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)) {
Do we need to test for MEMCG here? it seems this has been offloaded to
dma_buf_transfer_charge()?
> + ret = dma_buf_transfer_charge(file, target_proc->tsk);
> + if (unlikely(ret == -EBADF)) {
> + binder_user_error(
> + "%d:%d got transaction with XFER_CHARGE for non-DMA-BUF fd, %d\n",
> + proc->pid, thread->pid, fd);
> + goto err_dmabuf;
> + } else 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 +2309,8 @@ 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 +2621,7 @@ 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 +3400,8 @@ 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 ||
> diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h
> index e72e4de8f452..4b20dd1dccb1 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_FD_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
> @@ -162,7 +173,7 @@ 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;
> --
> 2.39.0.246.g2a6d74b583-goog
>
Other than the previous question this looks good to me. Also, the error
from the test robot seems to indicate a missing stub for
dma_buf_transfer_charg() when !CONFIG_DMA_SHARED_BUFFER. However, this
is likely to be fixed outside of this patch. Feel free to add this tag
to the following round:
Acked-by: Carlos Llamas <cmllamas at google.com>
Thanks,
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