Re: [RFC bpf-next v2 1/6] bpf: enable sleepable BPF programs attached to cgroup/{get,set}sockopt.

Stanislav Fomichev
2023-08-11T23:01:17Z

On 08/10, thinker.li@gmail.com wrote:
> From: Kui-Feng Lee <kuifeng@meta.com>
>
> Enable sleepable cgroup/{get,set}sockopt hooks.
>
> The sleepable BPF programs attached to cgroup/{get,set}sockopt hooks may
> received a pointer to the optval in user space instead of a kernel
> copy. ctx->user_optval and ctx->user_optval_end are the pointers to the
> begin and end of the user space buffer if receiving a user space
> buffer. ctx->optval and ctx->optval_end will be a kernel copy if receiving
> a kernel space buffer.
>
> A program receives a user space buffer if ctx->flags &
> BPF_SOCKOPT_FLAG_OPTVAL_USER is true, otherwise it receives a kernel space
> buffer. The BPF programs should not read/write from/to a user space buffer
> dirrectly. It should access the buffer through bpf_copy_from_user() and
> bpf_copy_to_user() provided in the following patches.
>
> Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
> ---
> include/linux/filter.h | 1 +
> include/uapi/linux/bpf.h | 7 +
> kernel/bpf/cgroup.c | 229 ++++++++++++++++++++++++++-------
> kernel/bpf/verifier.c | 7 +-
> tools/include/uapi/linux/bpf.h | 7 +
> tools/lib/bpf/libbpf.c | 2 +
> 6 files changed, 206 insertions(+), 47 deletions(-)
>
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 761af6b3cf2b..54169a641d40 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -1337,6 +1337,7 @@ struct bpf_sockopt_kern {
> s32 level;
> s32 optname;
> s32 optlen;
> + u32 flags;
> /* for retval in struct bpf_cg_run_ctx */
> struct task_struct *current_task;
> /* Temporary "register" for indirect stores to ppos. */
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 70da85200695..fff6f7dff408 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -7138,6 +7138,13 @@ struct bpf_sockopt {
> __s32 optname;
> __s32 optlen;
> __s32 retval;
> +
> + __u32 flags;
> +};
> +
> +enum bpf_sockopt_flags {
> + /* optval is a pointer to user space memory */
> + BPF_SOCKOPT_FLAG_OPTVAL_USER = (1U << 0),
> };
>
> struct bpf_pidns_info {
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index 5b2741aa0d9b..59489d9619a3 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -28,25 +28,46 @@ EXPORT_SYMBOL(cgroup_bpf_enabled_key);
> * function pointer.
> */
> static __always_inline int
> -bpf_prog_run_array_cg(const struct cgroup_bpf *cgrp,
> - enum cgroup_bpf_attach_type atype,
> - const void *ctx, bpf_prog_run_fn run_prog,
> - int retval, u32 *ret_flags)
> +bpf_prog_run_array_cg_cb(const struct cgroup_bpf *cgrp,
> + enum cgroup_bpf_attach_type atype,
> + const void *ctx, bpf_prog_run_fn run_prog,
> + int retval, u32 *ret_flags,
> + int (*progs_cb)(void *, const struct bpf_prog_array_item *),
> + void *progs_cb_arg)
> {
> const struct bpf_prog_array_item *item;
> const struct bpf_prog *prog;
> const struct bpf_prog_array *array;
> struct bpf_run_ctx *old_run_ctx;
> struct bpf_cg_run_ctx run_ctx;
> + bool do_sleepable;
> u32 func_ret;
> + int err;
> +
> + do_sleepable =
> + atype == CGROUP_SETSOCKOPT || atype == CGROUP_GETSOCKOPT;
>
> run_ctx.retval = retval;
> migrate_disable();
> - rcu_read_lock();
> + if (do_sleepable) {
> + might_fault();
> + rcu_read_lock_trace();
> + } else
> + rcu_read_lock();
> array = rcu_dereference(cgrp->effective[atype]);
> item = &array->items[0];
> +
> + if (progs_cb) {
> + err = progs_cb(progs_cb_arg, item);
> + if (err)
> + return err;
> + }
> +
> old_run_ctx = bpf_set_run_ctx(&run_ctx.run_ctx);
> while ((prog = READ_ONCE(item->prog))) {
> + if (do_sleepable && !prog->aux->sleepable)
> + rcu_read_lock();
> +
> run_ctx.prog_item = item;
> func_ret = run_prog(prog, ctx);
> if (ret_flags) {
> @@ -56,13 +77,48 @@ bpf_prog_run_array_cg(const struct cgroup_bpf *cgrp,
> if (!func_ret && !IS_ERR_VALUE((long)run_ctx.retval))
> run_ctx.retval = -EPERM;
> item++;
> +
> + if (do_sleepable && !prog->aux->sleepable)
> + rcu_read_unlock();
> }
> bpf_reset_run_ctx(old_run_ctx);
> - rcu_read_unlock();
> + if (do_sleepable)
> + rcu_read_unlock_trace();
> + else
> + rcu_read_unlock();
> migrate_enable();
> return run_ctx.retval;
> }
>
> +static __always_inline void
> +count_sleepable_prog_cg(const struct bpf_prog_array_item *item,
> + int *sleepable, int *non_sleepable)
> +{
> + const struct bpf_prog *prog;
> + bool ret = true;
> +
> + *sleepable = 0;
> + *non_sleepable = 0;
> +
> + while (ret && (prog = READ_ONCE(item->prog))) {
> + if (prog->aux->sleepable)
> + (*sleepable)++;
> + else
> + (*non_sleepable)++;
> + item++;
> + }
> +}

Can we maintain this info in the slow attach/detach path?
Running the loop every time we get a sockopt syscall another time
seems like something we can avoid? (even though it's a slow path,
seems like we can do better?)

> +
> +static __always_inline int
> +bpf_prog_run_array_cg(const struct cgroup_bpf *cgrp,
> + enum cgroup_bpf_attach_type atype,
> + const void *ctx, bpf_prog_run_fn run_prog,
> + int retval, u32 *ret_flags)
> +{
> + return bpf_prog_run_array_cg_cb(cgrp, atype, ctx, run_prog, retval,
> + ret_flags, NULL, NULL);
> +}
> +
> unsigned int __cgroup_bpf_run_lsm_sock(const void *ctx,
> const struct bpf_insn *insn)
> {
> @@ -307,7 +363,7 @@ static void cgroup_bpf_release(struct work_struct *work)
> old_array = rcu_dereference_protected(
> cgrp->bpf.effective[atype],
> lockdep_is_held(&cgroup_mutex));
> - bpf_prog_array_free(old_array);
> + bpf_prog_array_free_sleepable(old_array);
> }
>
> list_for_each_entry_safe(storage, stmp, storages, list_cg) {
> @@ -451,7 +507,7 @@ static void activate_effective_progs(struct cgroup *cgrp,
> /* free prog array after grace period, since __cgroup_bpf_run_*()
> * might be still walking the array
> */
> - bpf_prog_array_free(old_array);
> + bpf_prog_array_free_sleepable(old_array);
> }
>
> /**
> @@ -491,7 +547,7 @@ int cgroup_bpf_inherit(struct cgroup *cgrp)
> return 0;
> cleanup:
> for (i = 0; i < NR; i++)
> - bpf_prog_array_free(arrays[i]);
> + bpf_prog_array_free_sleepable(arrays[i]);
>
> for (p = cgroup_parent(cgrp); p; p = cgroup_parent(p))
> cgroup_bpf_put(p);
> @@ -525,7 +581,7 @@ static int update_effective_progs(struct cgroup *cgrp,
>
> if (percpu_ref_is_zero(&desc->bpf.refcnt)) {
> if (unlikely(desc->bpf.inactive)) {
> - bpf_prog_array_free(desc->bpf.inactive);
> + bpf_prog_array_free_sleepable(desc->bpf.inactive);
> desc->bpf.inactive = NULL;
> }
> continue;
> @@ -544,7 +600,7 @@ static int update_effective_progs(struct cgroup *cgrp,
> css_for_each_descendant_pre(css, &cgrp->self) {
> struct cgroup *desc = container_of(css, struct cgroup, self);
>
> - bpf_prog_array_free(desc->bpf.inactive);
> + bpf_prog_array_free_sleepable(desc->bpf.inactive);
> desc->bpf.inactive = NULL;
> }
>
> @@ -1740,7 +1796,7 @@ int __cgroup_bpf_run_filter_sysctl(struct ctl_table_header *head,
>
> #ifdef CONFIG_NET
> static int sockopt_alloc_buf(struct bpf_sockopt_kern *ctx, int max_optlen,
> - struct bpf_sockopt_buf *buf)
> + struct bpf_sockopt_buf *buf, bool force_alloc)
> {
> if (unlikely(max_optlen < 0))
> return -EINVAL;
> @@ -1752,7 +1808,7 @@ static int sockopt_alloc_buf(struct bpf_sockopt_kern *ctx, int max_optlen,
> max_optlen = PAGE_SIZE;
> }
>
> - if (max_optlen <= sizeof(buf->data)) {
> + if (max_optlen <= sizeof(buf->data) && !force_alloc) {
> /* When the optval fits into BPF_SOCKOPT_KERN_BUF_SIZE
> * bytes avoid the cost of kzalloc.
> */
> @@ -1773,7 +1829,8 @@ static int sockopt_alloc_buf(struct bpf_sockopt_kern *ctx, int max_optlen,
> static void sockopt_free_buf(struct bpf_sockopt_kern *ctx,
> struct bpf_sockopt_buf *buf)
> {
> - if (ctx->optval == buf->data)
> + if (ctx->optval == buf->data ||
> + ctx->flags & BPF_SOCKOPT_FLAG_OPTVAL_USER)
> return;
> kfree(ctx->optval);
> }
> @@ -1781,7 +1838,50 @@ static void sockopt_free_buf(struct bpf_sockopt_kern *ctx,
> static bool sockopt_buf_allocated(struct bpf_sockopt_kern *ctx,
> struct bpf_sockopt_buf *buf)
> {
> - return ctx->optval != buf->data;
> + return ctx->optval != buf->data &&
> + !(ctx->flags & BPF_SOCKOPT_FLAG_OPTVAL_USER);
> +}
> +
> +struct filter_sockopt_cb_args {
> + struct bpf_sockopt_kern *ctx;
> + struct bpf_sockopt_buf *buf;
> + int max_optlen;
> +};
> +
> +static int filter_setsockopt_progs_cb(void *arg,
> + const struct bpf_prog_array_item *item)
> +{
> + struct filter_sockopt_cb_args *cb_args = arg;
> + struct bpf_sockopt_kern *ctx = cb_args->ctx;
> + char *optval = ctx->optval;
> + int sleepable_cnt, non_sleepable_cnt;
> + int max_optlen;
> +
> + count_sleepable_prog_cg(item, &sleepable_cnt, &non_sleepable_cnt);
> +
> + if (!non_sleepable_cnt)
> + return 0;
> +
> + /* Allocate a bit more than the initial user buffer for
> + * BPF program. The canonical use case is overriding
> + * TCP_CONGESTION(nv) to TCP_CONGESTION(cubic).
> + */
> + max_optlen = max_t(int, 16, ctx->optlen);
> + /* We need to force allocating from heap if there are sleepable
> + * programs since they may created dynptrs from ctx->optval. In
> + * this case, dynptrs will try to free the buffer that is actually
> + * on the stack without this flag.
> + */
> + max_optlen = sockopt_alloc_buf(ctx, max_optlen, cb_args->buf,
> + !!sleepable_cnt);
> + if (max_optlen < 0)
> + return max_optlen;
> +
> + if (copy_from_user(ctx->optval, optval,
> + min(ctx->optlen, max_optlen)) != 0)
> + return -EFAULT;
> +
> + return 0;
> }
>
> int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level,
> @@ -1795,27 +1895,22 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level,
> .level = *level,
> .optname = *optname,
> };
> + struct filter_sockopt_cb_args cb_args = {
> + .ctx = &ctx,
> + .buf = &buf,
> + };
> int ret, max_optlen;
>
> - /* Allocate a bit more than the initial user buffer for
> - * BPF program. The canonical use case is overriding
> - * TCP_CONGESTION(nv) to TCP_CONGESTION(cubic).
> - */
> - max_optlen = max_t(int, 16, *optlen);
> - max_optlen = sockopt_alloc_buf(&ctx, max_optlen, &buf);
> - if (max_optlen < 0)
> - return max_optlen;
> -
> + max_optlen = *optlen;
> ctx.optlen = *optlen;
> -
> - if (copy_from_user(ctx.optval, optval, min(*optlen, max_optlen)) != 0) {
> - ret = -EFAULT;
> - goto out;
> - }
> + ctx.optval = optval;
> + ctx.optval_end = optval + *optlen;
> + ctx.flags = BPF_SOCKOPT_FLAG_OPTVAL_USER;
>
> lock_sock(sk);
> - ret = bpf_prog_run_array_cg(&cgrp->bpf, CGROUP_SETSOCKOPT,
> - &ctx, bpf_prog_run, 0, NULL);
> + ret = bpf_prog_run_array_cg_cb(&cgrp->bpf, CGROUP_SETSOCKOPT,
> + &ctx, bpf_prog_run, 0, NULL,
> + filter_setsockopt_progs_cb, &cb_args);
> release_sock(sk);
>
> if (ret)
> @@ -1824,7 +1919,8 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level,
> if (ctx.optlen == -1) {
> /* optlen set to -1, bypass kernel */
> ret = 1;
> - } else if (ctx.optlen > max_optlen || ctx.optlen < -1) {
> + } else if (ctx.optlen > (ctx.optval_end - ctx.optval) ||
> + ctx.optlen < -1) {
> /* optlen is out of bounds */
> if (*optlen > PAGE_SIZE && ctx.optlen >= 0) {
> pr_info_once("bpf setsockopt: ignoring program buffer with optlen=%d (max_optlen=%d)\n",
> @@ -1846,6 +1942,8 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level,
> */
> if (ctx.optlen != 0) {
> *optlen = ctx.optlen;
> + if (ctx.flags & BPF_SOCKOPT_FLAG_OPTVAL_USER)
> + return 0;
> /* We've used bpf_sockopt_kern->buf as an intermediary
> * storage, but the BPF program indicates that we need
> * to pass this data to the kernel setsockopt handler.
> @@ -1874,6 +1972,36 @@ int __cgroup_bpf_run_filter_setsockopt(struct sock *sk, int *level,
> return ret;
> }
>
> +static int filter_getsockopt_progs_cb(void *arg,
> + const struct bpf_prog_array_item *item)
> +{
> + struct filter_sockopt_cb_args *cb_args = arg;
> + struct bpf_sockopt_kern *ctx = cb_args->ctx;
> + int sleepable_cnt, non_sleepable_cnt;
> + int max_optlen;
> + char *optval;
> +
> + count_sleepable_prog_cg(item, &sleepable_cnt, &non_sleepable_cnt);
> +
> + if (!non_sleepable_cnt)
> + return 0;
> +
> + optval = ctx->optval;
> + max_optlen = sockopt_alloc_buf(ctx, cb_args->max_optlen,
> + cb_args->buf, false);
> + if (max_optlen < 0)
> + return max_optlen;
> +
> + if (copy_from_user(ctx->optval, optval,
> + min(ctx->optlen, max_optlen)) != 0)
> + return -EFAULT;
> +
> + ctx->flags = 0;
> + cb_args->max_optlen = max_optlen;
> +
> + return 0;
> +}
> +
> int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level,
> int optname, char __user *optval,
> int __user *optlen, int max_optlen,
> @@ -1887,15 +2015,16 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level,
> .optname = optname,
> .current_task = current,
> };
> + struct filter_sockopt_cb_args cb_args = {
> + .ctx = &ctx,
> + .buf = &buf,
> + .max_optlen = max_optlen,
> + };
> int orig_optlen;
> int ret;
>
> orig_optlen = max_optlen;
> ctx.optlen = max_optlen;
> - max_optlen = sockopt_alloc_buf(&ctx, max_optlen, &buf);
> - if (max_optlen < 0)
> - return max_optlen;
> -
> if (!retval) {
> /* If kernel getsockopt finished successfully,
> * copy whatever was returned to the user back
> @@ -1914,18 +2043,19 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level,
> goto out;
> }
> orig_optlen = ctx.optlen;
> -
> - if (copy_from_user(ctx.optval, optval,
> - min(ctx.optlen, max_optlen)) != 0) {
> - ret = -EFAULT;
> - goto out;
> - }
> }
>
> + ctx.optval = optval;
> + ctx.optval_end = optval + max_optlen;
> + ctx.flags = BPF_SOCKOPT_FLAG_OPTVAL_USER;
> +
> lock_sock(sk);
> - ret = bpf_prog_run_array_cg(&cgrp->bpf, CGROUP_GETSOCKOPT,
> - &ctx, bpf_prog_run, retval, NULL);
> + ret = bpf_prog_run_array_cg_cb(&cgrp->bpf, CGROUP_GETSOCKOPT,
> + &ctx, bpf_prog_run, retval, NULL,
> + filter_getsockopt_progs_cb,
> + &cb_args);
> release_sock(sk);
> + max_optlen = cb_args.max_optlen;
>
> if (ret < 0)
> goto out;
> @@ -1942,7 +2072,9 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level,
> }
>
> if (ctx.optlen != 0) {
> - if (optval && copy_to_user(optval, ctx.optval, ctx.optlen)) {
> + if (optval &&
> + !(ctx.flags & BPF_SOCKOPT_FLAG_OPTVAL_USER) &&
> + copy_to_user(optval, ctx.optval, ctx.optlen)) {
> ret = -EFAULT;
> goto out;
> }
> @@ -2388,6 +2520,10 @@ static bool cg_sockopt_is_valid_access(int off, int size,
> if (size != size_default)
> return false;
> return prog->expected_attach_type == BPF_CGROUP_GETSOCKOPT;
> + case offsetof(struct bpf_sockopt, flags):
> + if (size != sizeof(__u32))
> + return false;
> + break;
> default:
> if (size != size_default)
> return false;
> @@ -2481,6 +2617,9 @@ static u32 cg_sockopt_convert_ctx_access(enum bpf_access_type type,
> case offsetof(struct bpf_sockopt, optval_end):
> *insn++ = CG_SOCKOPT_READ_FIELD(optval_end);
> break;
> + case offsetof(struct bpf_sockopt, flags):
> + *insn++ = CG_SOCKOPT_READ_FIELD(flags);
> + break;
> }
>
> return insn - insn_buf;
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 132f25dab931..fbc0096693e7 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -19538,9 +19538,11 @@ static bool can_be_sleepable(struct bpf_prog *prog)
> return false;
> }
> }
> +

Extra newline?

> return prog->type == BPF_PROG_TYPE_LSM ||
> prog->type == BPF_PROG_TYPE_KPROBE /* only for uprobes */ ||
> - prog->type == BPF_PROG_TYPE_STRUCT_OPS;
> + prog->type == BPF_PROG_TYPE_STRUCT_OPS ||
> + prog->type == BPF_PROG_TYPE_CGROUP_SOCKOPT;
> }
>
> static int check_attach_btf_id(struct bpf_verifier_env *env)
> @@ -19562,7 +19564,8 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
> }
>
> if (prog->aux->sleepable && !can_be_sleepable(prog)) {
> - verbose(env, "Only fentry/fexit/fmod_ret, lsm, iter, uprobe, and struct_ops programs can be sleepable\n");
> + verbose(env, "Only fentry/fexit/fmod_ret, lsm, iter, uprobe,"
> + "cgroup, and struct_ops programs can be sleepable\n");

I don't think we split the lines even if they are too long.
Makes them ungreppable :-(

> return -EINVAL;
> }
>
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 70da85200695..fff6f7dff408 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -7138,6 +7138,13 @@ struct bpf_sockopt {
> __s32 optname;
> __s32 optlen;
> __s32 retval;
> +
> + __u32 flags;
> +};
> +
> +enum bpf_sockopt_flags {
> + /* optval is a pointer to user space memory */
> + BPF_SOCKOPT_FLAG_OPTVAL_USER = (1U << 0),
> };

Why do we need to export the flag? Do we still want the users
to do something based on the presence/absence of
BPF_SOCKOPT_FLAG_OPTVAL_USER?