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Message-ID: <20250814134917.GE802098@nvidia.com>
Date: Thu, 14 Aug 2025 10:49:17 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Pasha Tatashin <pasha.tatashin@...een.com>
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Subject: Re: [PATCH v3 16/30] liveupdate: luo_ioctl: add userpsace interface
On Thu, Aug 07, 2025 at 01:44:22AM +0000, Pasha Tatashin wrote:
> +/**
> + * DOC: General ioctl format
> + *
> + * The ioctl interface follows a general format to allow for extensibility. Each
> + * ioctl is passed in a structure pointer as the argument providing the size of
> + * the structure in the first u32. The kernel checks that any structure space
> + * beyond what it understands is 0. This allows userspace to use the backward
> + * compatible portion while consistently using the newer, larger, structures.
> + *
> + * ioctls use a standard meaning for common errnos:
> + *
> + * - ENOTTY: The IOCTL number itself is not supported at all
> + * - E2BIG: The IOCTL number is supported, but the provided structure has
> + * non-zero in a part the kernel does not understand.
> + * - EOPNOTSUPP: The IOCTL number is supported, and the structure is
> + * understood, however a known field has a value the kernel does not
> + * understand or support.
> + * - EINVAL: Everything about the IOCTL was understood, but a field is not
> + * correct.
> + * - ENOENT: An ID or IOVA provided does not exist.
^^^^^^^^^
Maybe this should be 'token' ?
> + * - ENOMEM: Out of memory.
> + * - EOVERFLOW: Mathematics overflowed.
> + *
> + * As well as additional errnos, within specific ioctls.
> + */
Ah if you copy the comment make sure to faithfully follow it in the
implementation :)
> +struct liveupdate_ioctl_fd_unpreserve {
> + __u32 size;
> + __aligned_u64 token;
> +};
It is best to explicitly pad, so add a __u32 reserved between size and
token
Then you need to also check that the reserved is 0 when parsing it,
return -EOPNOTSUPP otherwise.
> +static atomic_t luo_device_in_use = ATOMIC_INIT(0);
I suggest you bundle this together into one struct with the misc_dev
and the other globals and largely pretend it is not global, eg refer
to it through container_of, etc
Following practices like this make it harder to abuse the globals.
> +struct luo_ucmd {
> + void __user *ubuffer;
> + u32 user_size;
> + void *cmd;
> +};
> +
> +static int luo_ioctl_fd_preserve(struct luo_ucmd *ucmd)
> +{
> + struct liveupdate_ioctl_fd_preserve *argp = ucmd->cmd;
> + int ret;
> +
> + ret = luo_register_file(argp->token, argp->fd);
> + if (!ret)
> + return ret;
> +
> + if (copy_to_user(ucmd->ubuffer, argp, ucmd->user_size))
> + return -EFAULT;
This will overflow memory, ucmd->user_size may be > sizeof(*argp)
The respond function is an important part of this scheme:
static inline int iommufd_ucmd_respond(struct iommufd_ucmd *ucmd,
size_t cmd_len)
{
if (copy_to_user(ucmd->ubuffer, ucmd->cmd,
min_t(size_t, ucmd->user_size, cmd_len)))
return -EFAULT;
The min (sizeof(*argp) in this case) can't be skipped!
> +static int luo_ioctl_fd_restore(struct luo_ucmd *ucmd)
> +{
> + struct liveupdate_ioctl_fd_restore *argp = ucmd->cmd;
> + struct file *file;
> + int ret;
> +
> + argp->fd = get_unused_fd_flags(O_CLOEXEC);
> + if (argp->fd < 0) {
> + pr_err("Failed to allocate new fd: %d\n", argp->fd);
No need
> + return argp->fd;
> + }
> +
> + ret = luo_retrieve_file(argp->token, &file);
> + if (ret < 0) {
> + put_unused_fd(argp->fd);
> +
> + return ret;
> + }
> +
> + fd_install(argp->fd, file);
> +
> + if (copy_to_user(ucmd->ubuffer, argp, ucmd->user_size))
> + return -EFAULT;
Wrong order, fd_install must be last right before return 0. Failing
system calls should not leave behind installed FDs.
> +static int luo_ioctl_set_event(struct luo_ucmd *ucmd)
> +{
> + struct liveupdate_ioctl_set_event *argp = ucmd->cmd;
> + int ret;
> +
> + switch (argp->event) {
> + case LIVEUPDATE_PREPARE:
> + ret = luo_prepare();
> + break;
> + case LIVEUPDATE_FINISH:
> + ret = luo_finish();
> + break;
> + case LIVEUPDATE_CANCEL:
> + ret = luo_cancel();
> + break;
> + default:
> + ret = -EINVAL;
EOPNOTSUPP
> +union ucmd_buffer {
> + struct liveupdate_ioctl_fd_preserve preserve;
> + struct liveupdate_ioctl_fd_unpreserve unpreserve;
> + struct liveupdate_ioctl_fd_restore restore;
> + struct liveupdate_ioctl_get_state state;
> + struct liveupdate_ioctl_set_event event;
> +};
I discourage the column alignment. Also sort by name.
> +static const struct luo_ioctl_op luo_ioctl_ops[] = {
> + IOCTL_OP(LIVEUPDATE_IOCTL_FD_PRESERVE, luo_ioctl_fd_preserve,
> + struct liveupdate_ioctl_fd_preserve, token),
> + IOCTL_OP(LIVEUPDATE_IOCTL_FD_UNPRESERVE, luo_ioctl_fd_unpreserve,
> + struct liveupdate_ioctl_fd_unpreserve, token),
> + IOCTL_OP(LIVEUPDATE_IOCTL_FD_RESTORE, luo_ioctl_fd_restore,
> + struct liveupdate_ioctl_fd_restore, token),
> + IOCTL_OP(LIVEUPDATE_IOCTL_GET_STATE, luo_ioctl_get_state,
> + struct liveupdate_ioctl_get_state, state),
> + IOCTL_OP(LIVEUPDATE_IOCTL_SET_EVENT, luo_ioctl_set_event,
> + struct liveupdate_ioctl_set_event, event),
Sort by name
Jason
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