[RFC bpf-next v3 1/5] bpf: enable sleepable BPF programs attached to cgroup/{get,set}sockopt.

thinker.li
2023-08-15T17:47:32Z

From: Kui-Feng Lee <thinker.li@gmail.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/bpf.h | 6 ++
include/linux/filter.h | 6 ++
kernel/bpf/cgroup.c | 207 ++++++++++++++++++++++++++++++++---------
kernel/bpf/verifier.c | 5 +-
4 files changed, 177 insertions(+), 47 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index cfabbcf47bdb..edb35bcfa548 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1769,9 +1769,15 @@ struct bpf_prog_array_item {

struct bpf_prog_array {
struct rcu_head rcu;
+ u32 flags;
struct bpf_prog_array_item items[];
};

+enum bpf_prog_array_flags {
+ BPF_PROG_ARRAY_F_SLEEPABLE = 1 << 0,
+ BPF_PROG_ARRAY_F_NON_SLEEPABLE = 1 << 1,
+};
+
struct bpf_empty_prog_array {
struct bpf_prog_array hdr;
struct bpf_prog *null_prog;
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 761af6b3cf2b..2aa2a96526de 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1337,12 +1337,18 @@ 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. */
u64 tmp_reg;
};

+enum bpf_sockopt_kern_flags {
+ /* optval is a pointer to user space memory */
+ BPF_SOCKOPT_FLAG_OPTVAL_USER = (1U << 0),
+};
+
int copy_bpf_fprog_from_user(struct sock_fprog *dst, sockptr_t src, int len);

struct bpf_sk_lookup_kern {
diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
index 5b2741aa0d9b..b977768a28e5 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 *),
+ 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, array);
+ 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 +77,29 @@ 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 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 +344,7 @@ 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) {
@@ -402,6 +439,7 @@ static int compute_effective_progs(struct cgroup *cgrp,
enum cgroup_bpf_attach_type atype,
struct bpf_prog_array **array)
{
+ bool has_non_sleepable = false, has_sleepable = false;
struct bpf_prog_array_item *item;
struct bpf_prog_array *progs;
struct bpf_prog_list *pl;
@@ -434,10 +472,19 @@ static int compute_effective_progs(struct cgroup *cgrp,
item->prog = prog_list_prog(pl);
bpf_cgroup_storages_assign(item->cgroup_storage,
pl->storage);
+ if (item->prog->aux->sleepable)
+ has_sleepable = true;
+ else
+ has_non_sleepable = true;
cnt++;
}
} while ((p = cgroup_parent(p)));

+ if (has_non_sleepable)
+ progs->flags |= BPF_PROG_ARRAY_F_NON_SLEEPABLE;
+ if (has_sleepable)
+ progs->flags |= BPF_PROG_ARRAY_F_SLEEPABLE;
+
*array = progs;
return 0;
}
@@ -451,7 +498,7 @@ 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 +538,7 @@ 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 +572,7 @@ 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 +591,7 @@ 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 +1787,7 @@ 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 +1799,7 @@ 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 +1820,8 @@ 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 +1829,47 @@ 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 *progs)
+{
+ struct filter_sockopt_cb_args *cb_args = arg;
+ struct bpf_sockopt_kern *ctx = cb_args->ctx;
+ char *optval = ctx->optval;
+ int max_optlen;
+
+ if (!(progs->flags & BPF_PROG_ARRAY_F_NON_SLEEPABLE))
+ 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,
+ progs->flags & BPF_PROG_ARRAY_F_SLEEPABLE);
+ 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 +1883,22 @@ 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 +1907,8 @@ 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 +1930,8 @@ 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 +1960,33 @@ 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 *progs)
+{
+ struct filter_sockopt_cb_args *cb_args = arg;
+ struct bpf_sockopt_kern *ctx = cb_args->ctx;
+ int max_optlen;
+ char *optval;
+
+ if (!(progs->flags & BPF_PROG_ARRAY_F_NON_SLEEPABLE))
+ 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 +2000,16 @@ 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 +2028,19 @@ 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 +2057,9 @@ 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;
}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 4ccca1f6c998..61be432b9420 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -19549,7 +19549,8 @@ static bool can_be_sleepable(struct bpf_prog *prog)
}
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)
@@ -19571,7 +19572,7 @@ 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");
return -EINVAL;
}

--
2.34.1