[LibreQoS] Fwd: [PATCH v2 bpf-next 09/13] bpf: Special verifier handling for bpf_rbtree_{remove, first}
Dave Taht
dave.taht at gmail.com
Sat Dec 17 12:46:34 EST 2022
BPF is becoming an OS all by itself. If we were to rewrite cake to be
one instance per cpu across all subscribers, we might schedule packets
via the rbtree facility, or perhaps a timerwheel.
---------- Forwarded message ---------
From: Dave Marchevsky <davemarchevsky at fb.com>
Date: Sat, Dec 17, 2022 at 12:42 AM
Subject: [PATCH v2 bpf-next 09/13] bpf: Special verifier handling for
bpf_rbtree_{remove, first}
To: <bpf at vger.kernel.org>
Cc: Alexei Starovoitov <ast at kernel.org>, Daniel Borkmann
<daniel at iogearbox.net>, Andrii Nakryiko <andrii at kernel.org>, Kernel
Team <kernel-team at fb.com>, Kumar Kartikeya Dwivedi <memxor at gmail.com>,
Tejun Heo <tj at kernel.org>, Dave Marchevsky <davemarchevsky at fb.com>
Newly-added bpf_rbtree_{remove,first} kfuncs have some special properties
that require handling in the verifier:
* both bpf_rbtree_remove and bpf_rbtree_first return the type containing
the bpf_rb_node field, with the offset set to that field's offset,
instead of a struct bpf_rb_node *
* mark_reg_graph_node helper added in previous patch generalizes
this logic, use it
* bpf_rbtree_remove's node input is a node that's been inserted
in the tree - a non-owning reference.
* bpf_rbtree_remove must invalidate non-owning references in order to
avoid aliasing issue. Add KF_INVALIDATE_NON_OWN flag, which
indicates that the marked kfunc is a non-owning ref invalidation
point, and associated verifier logic using previously-added
invalidate_non_owning_refs helper.
* Unlike other functions, which convert one of their input arg regs to
non-owning reference, bpf_rbtree_first takes no arguments and just
returns a non-owning reference (possibly null)
* For now verifier logic for this is special-cased instead of
adding new kfunc flag.
This patch, along with the previous one, complete special verifier
handling for all rbtree API functions added in this series.
Signed-off-by: Dave Marchevsky <davemarchevsky at fb.com>
---
include/linux/btf.h | 1 +
kernel/bpf/helpers.c | 2 +-
kernel/bpf/verifier.c | 34 ++++++++++++++++++++++++++++------
3 files changed, 30 insertions(+), 7 deletions(-)
diff --git a/include/linux/btf.h b/include/linux/btf.h
index 8aee3f7f4248..3663911bb7c0 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -72,6 +72,7 @@
#define KF_DESTRUCTIVE (1 << 6) /* kfunc performs destructive
actions */
#define KF_RCU (1 << 7) /* kfunc only takes rcu
pointer arguments */
#define KF_RELEASE_NON_OWN (1 << 8) /* kfunc converts its
referenced arg into non-owning ref */
+#define KF_INVALIDATE_NON_OWN (1 << 9) /* kfunc invalidates
non-owning refs after return */
/*
* Return the name of the passed struct, if exists, or halt the build if for
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index de4523c777b7..0e6d010e6423 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2121,7 +2121,7 @@ BTF_ID_FLAGS(func, bpf_task_acquire, KF_ACQUIRE
| KF_TRUSTED_ARGS)
BTF_ID_FLAGS(func, bpf_task_acquire_not_zero, KF_ACQUIRE | KF_RCU |
KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_task_kptr_get, KF_ACQUIRE | KF_KPTR_GET | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_task_release, KF_RELEASE)
-BTF_ID_FLAGS(func, bpf_rbtree_remove, KF_ACQUIRE)
+BTF_ID_FLAGS(func, bpf_rbtree_remove, KF_ACQUIRE | KF_INVALIDATE_NON_OWN)
BTF_ID_FLAGS(func, bpf_rbtree_add, KF_RELEASE | KF_RELEASE_NON_OWN)
BTF_ID_FLAGS(func, bpf_rbtree_first, KF_RET_NULL)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 75979f78399d..b4bf3701de7f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -8393,6 +8393,11 @@ static bool is_kfunc_release_non_own(struct
bpf_kfunc_call_arg_meta *meta)
return meta->kfunc_flags & KF_RELEASE_NON_OWN;
}
+static bool is_kfunc_invalidate_non_own(struct bpf_kfunc_call_arg_meta *meta)
+{
+ return meta->kfunc_flags & KF_INVALIDATE_NON_OWN;
+}
+
static bool is_kfunc_trusted_args(struct bpf_kfunc_call_arg_meta *meta)
{
return meta->kfunc_flags & KF_TRUSTED_ARGS;
@@ -9425,10 +9430,20 @@ static int check_kfunc_args(struct
bpf_verifier_env *env, struct bpf_kfunc_call_
verbose(env, "arg#%d expected pointer
to allocated object\n", i);
return -EINVAL;
}
- if (!reg->ref_obj_id) {
+ if (meta->func_id ==
special_kfunc_list[KF_bpf_rbtree_remove]) {
+ if (reg->ref_obj_id) {
+ verbose(env, "rbtree_remove
node input must be non-owning ref\n");
+ return -EINVAL;
+ }
+ if (in_rbtree_lock_required_cb(env)) {
+ verbose(env, "rbtree_remove
not allowed in rbtree cb\n");
+ return -EINVAL;
+ }
+ } else if (!reg->ref_obj_id) {
verbose(env, "allocated object must be
referenced\n");
return -EINVAL;
}
+
ret = process_kf_arg_ptr_to_rbtree_node(env,
reg, regno, meta);
if (ret < 0)
return ret;
@@ -9665,11 +9680,12 @@ static int check_kfunc_call(struct
bpf_verifier_env *env, struct bpf_insn *insn,
meta.func_id ==
special_kfunc_list[KF_bpf_list_pop_back]) {
struct btf_field *field =
meta.arg_list_head.field;
- mark_reg_known_zero(env, regs, BPF_REG_0);
- regs[BPF_REG_0].type = PTR_TO_BTF_ID |
MEM_ALLOC;
- regs[BPF_REG_0].btf = field->graph_root.btf;
- regs[BPF_REG_0].btf_id =
field->graph_root.value_btf_id;
- regs[BPF_REG_0].off =
field->graph_root.node_offset;
+ mark_reg_graph_node(regs, BPF_REG_0,
&field->graph_root);
+ } else if (meta.func_id ==
special_kfunc_list[KF_bpf_rbtree_remove] ||
+ meta.func_id ==
special_kfunc_list[KF_bpf_rbtree_first]) {
+ struct btf_field *field =
meta.arg_rbtree_root.field;
+
+ mark_reg_graph_node(regs, BPF_REG_0,
&field->graph_root);
} else if (meta.func_id ==
special_kfunc_list[KF_bpf_cast_to_kern_ctx]) {
mark_reg_known_zero(env, regs, BPF_REG_0);
regs[BPF_REG_0].type = PTR_TO_BTF_ID |
PTR_TRUSTED;
@@ -9735,7 +9751,13 @@ static int check_kfunc_call(struct
bpf_verifier_env *env, struct bpf_insn *insn,
if (is_kfunc_ret_null(&meta))
regs[BPF_REG_0].id = id;
regs[BPF_REG_0].ref_obj_id = id;
+ } else if (meta.func_id ==
special_kfunc_list[KF_bpf_rbtree_first]) {
+ ref_set_non_owning_lock(env, ®s[BPF_REG_0]);
}
+
+ if (is_kfunc_invalidate_non_own(&meta))
+ invalidate_non_owning_refs(env,
&env->cur_state->active_lock);
+
if (reg_may_point_to_spin_lock(®s[BPF_REG_0]) &&
!regs[BPF_REG_0].id)
regs[BPF_REG_0].id = ++env->id_gen;
} /* else { add_kfunc_call() ensures it is btf_type_is_void(t) } */
--
2.30.2
--
This song goes out to all the folk that thought Stadia would work:
https://www.linkedin.com/posts/dtaht_the-mushroom-song-activity-6981366665607352320-FXtz
Dave Täht CEO, TekLibre, LLC
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