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sched_ext: Reject direct slice and dsq_vtime writes for cid-form schedulers

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Direct writes to p->scx.slice and p->scx.dsq_vtime bypass
scx_bpf_task_set_slice/dsq_vtime() and the authority checks they carry.
Those checks exist for sub-schedulers, which attach only through the
cid-form struct_ops, so the direct writes only need to be closed there.

Give sched_ext_ops_cid its own verifier ops that reject the two fields.
cid-form is a new interface with no legacy users, so there is no
compatibility to keep. The cpu-form keeps direct writes, and the deprecation
warning they carried is dropped.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
This commit is contained in:
Tejun Heo 2026-07-09 12:06:11 -10:00
parent c89b7a09b7
commit 31645fb113
1 changed files with 32 additions and 12 deletions
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44
kernel/sched/ext/ext.c
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@ -7026,6 +7026,21 @@ static bool bpf_scx_is_valid_access(int off, int size,
return btf_ctx_access(off, size, type, prog, info);
}
/* common to both forms: only scx.disallow is writable */
static int bpf_scx_btf_struct_access_common(const struct bpf_reg_state *reg,
int off, int size)
{
const struct btf_type *t;
t = btf_type_by_id(reg->btf, reg->btf_id);
if (t == task_struct_type &&
off >= offsetof(struct task_struct, scx.disallow) &&
off + size <= offsetofend(struct task_struct, scx.disallow))
return SCALAR_VALUE;
return -EACCES;
}
static int bpf_scx_btf_struct_access(struct bpf_verifier_log *log,
const struct bpf_reg_state *reg, int off,
int size)
@ -7034,23 +7049,22 @@ static int bpf_scx_btf_struct_access(struct bpf_verifier_log *log,
t = btf_type_by_id(reg->btf, reg->btf_id);
if (t == task_struct_type) {
/*
* COMPAT: Will be removed in v6.23.
*/
if ((off >= offsetof(struct task_struct, scx.slice) &&
off + size <= offsetofend(struct task_struct, scx.slice)) ||
(off >= offsetof(struct task_struct, scx.dsq_vtime) &&
off + size <= offsetofend(struct task_struct, scx.dsq_vtime))) {
pr_warn_ratelimited("sched_ext: Writing directly to p->scx.slice/dsq_vtime is deprecated, use scx_bpf_task_set_slice/dsq_vtime()\n");
return SCALAR_VALUE;
}
if (off >= offsetof(struct task_struct, scx.disallow) &&
off + size <= offsetofend(struct task_struct, scx.disallow))
off + size <= offsetofend(struct task_struct, scx.dsq_vtime)))
return SCALAR_VALUE;
}
return -EACCES;
return bpf_scx_btf_struct_access_common(reg, off, size);
}
/* cid-form rejects direct slice and dsq_vtime writes in favor of the kfuncs */
static int bpf_scx_cid_btf_struct_access(struct bpf_verifier_log *log,
const struct bpf_reg_state *reg, int off,
int size)
{
return bpf_scx_btf_struct_access_common(reg, off, size);
}
static const struct bpf_verifier_ops bpf_scx_verifier_ops = {
@ -7059,6 +7073,12 @@ static const struct bpf_verifier_ops bpf_scx_verifier_ops = {
.btf_struct_access = bpf_scx_btf_struct_access,
};
static const struct bpf_verifier_ops bpf_scx_cid_verifier_ops = {
.get_func_proto = bpf_base_func_proto,
.is_valid_access = bpf_scx_is_valid_access,
.btf_struct_access = bpf_scx_cid_btf_struct_access,
};
static int bpf_scx_init_member(const struct btf_type *t,
const struct btf_member *member,
void *kdata, const void *udata)
@ -7399,7 +7419,7 @@ static struct sched_ext_ops_cid __bpf_ops_sched_ext_ops_cid = {
* verified to match by the BUILD_BUG_ON checks in scx_init().
*/
static struct bpf_struct_ops bpf_sched_ext_ops_cid = {
.verifier_ops = &bpf_scx_verifier_ops,
.verifier_ops = &bpf_scx_cid_verifier_ops,
.reg = bpf_scx_reg_cid,
.unreg = bpf_scx_unreg,
.check_member = bpf_scx_check_member,