With private stack support, each subprog can have stack with up to 512
bytes. The limit of 512 bytes per subprog is kept to avoid increasing
verifier complexity since greater than 512 bytes will cause big verifier
change and increase memory consumption and verification time.
If private stack is supported, for a bpf prog, esp. when it has
subprogs, private stack will be allocated for the main prog
and for each callback subprog. For example,
main_prog
subprog1
calling helper
subprog10 (callback func)
subprog11
subprog2
calling helper
subprog10 (callback func)
subprog11
Separate private allocations for main_prog and callback_fn subprog10
will make things easier since the helper function uses the kernel stack.
In this patch, some tracing programs are allowed to use private
stack since tracing prog may be triggered in the middle of some other
prog runs. Additional subprog info is also collected for later to
allocate private stack for main prog and each callback functions.
Note that if any tail_call is called in the prog (including all subprogs),
then private stack is not used.
Signed-off-by: Yonghong Song <yonghong.song@xxxxxxxxx>
---
include/linux/bpf.h | 1 +
include/linux/bpf_verifier.h | 3 ++
include/linux/filter.h | 1 +
kernel/bpf/core.c | 5 ++
kernel/bpf/verifier.c | 100 ++++++++++++++++++++++++++++++-----
5 files changed, 97 insertions(+), 13 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 0c216e71cec7..6ad8ace7075a 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1490,6 +1490,7 @@ struct bpf_prog_aux {
bool exception_cb;
bool exception_boundary;
bool is_extended; /* true if extended by freplace program */
+ bool priv_stack_eligible;
u64 prog_array_member_cnt; /* counts how many times as member of prog_array */
struct mutex ext_mutex; /* mutex for is_extended and prog_array_member_cnt */
struct bpf_arena *arena;
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 4513372c5bc8..bcfe868e3801 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -659,6 +659,8 @@ struct bpf_subprog_info {
* are used for bpf_fastcall spills and fills.
*/
s16 fastcall_stack_off;
+ u16 subtree_stack_depth;
+ u16 subtree_top_idx;
bool has_tail_call: 1;
bool tail_call_reachable: 1;
bool has_ld_abs: 1;
@@ -668,6 +670,7 @@ struct bpf_subprog_info {
bool args_cached: 1;
/* true if bpf_fastcall stack region is used by functions that can't be inlined */
bool keep_fastcall_stack: 1;
+ bool priv_stack_eligible: 1;
u8 arg_cnt;
struct bpf_subprog_arg_info args[MAX_BPF_FUNC_REG_ARGS];
diff --git a/include/linux/filter.h b/include/linux/filter.h
index 7d7578a8eac1..3a21947f2fd4 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1119,6 +1119,7 @@ bool bpf_jit_supports_exceptions(void);
bool bpf_jit_supports_ptr_xchg(void);
bool bpf_jit_supports_arena(void);
bool bpf_jit_supports_insn(struct bpf_insn *insn, bool in_arena);
+bool bpf_jit_supports_private_stack(void);
u64 bpf_arch_uaddress_limit(void);
void arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie);
bool bpf_helper_changes_pkt_data(void *func);
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 233ea78f8f1b..14d9288441f2 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -3045,6 +3045,11 @@ bool __weak bpf_jit_supports_exceptions(void)
return false;
}
+bool __weak bpf_jit_supports_private_stack(void)
+{
+ return false;
+}
+
void __weak arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie)
{
}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f514247ba8ba..45bea4066272 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -194,6 +194,8 @@ struct bpf_verifier_stack_elem {
#define BPF_GLOBAL_PERCPU_MA_MAX_SIZE 512
+#define BPF_PRIV_STACK_MIN_SUBTREE_SIZE 128
+
static int acquire_reference_state(struct bpf_verifier_env *env, int insn_idx);
static int release_reference(struct bpf_verifier_env *env, int ref_obj_id);
static void invalidate_non_owning_refs(struct bpf_verifier_env *env);
@@ -5982,6 +5984,41 @@ static int check_ptr_alignment(struct bpf_verifier_env *env,
strict);
}
+static bool bpf_enable_private_stack(struct bpf_verifier_env *env)
+{
+ if (!bpf_jit_supports_private_stack())
+ return false;
+
+ switch (env->prog->type) {
+ case BPF_PROG_TYPE_KPROBE:
+ case BPF_PROG_TYPE_TRACEPOINT:
+ case BPF_PROG_TYPE_PERF_EVENT:
+ case BPF_PROG_TYPE_RAW_TRACEPOINT:
+ return true;
+ case BPF_PROG_TYPE_TRACING:
+ if (env->prog->expected_attach_type != BPF_TRACE_ITER)
+ return true;
+ fallthrough;
+ default:
+ return false;
+ }
+}
+
+static bool is_priv_stack_supported(struct bpf_verifier_env *env)
+{
+ struct bpf_subprog_info *si = env->subprog_info;
+ bool has_tail_call = false;
+
+ for (int i = 0; i < env->subprog_cnt; i++) {
+ if (si[i].has_tail_call) {
+ has_tail_call = true;
+ break;
+ }
+ }
+
+ return !has_tail_call && bpf_enable_private_stack(env);
+}
+
static int round_up_stack_depth(struct bpf_verifier_env *env, int stack_depth)
{
if (env->prog->jit_requested)
@@ -5999,16 +6036,21 @@ static int round_up_stack_depth(struct bpf_verifier_env *env, int stack_depth)
* Since recursion is prevented by check_cfg() this algorithm
* only needs a local stack of MAX_CALL_FRAMES to remember callsites
*/
-static int check_max_stack_depth_subprog(struct bpf_verifier_env *env, int idx)
+static int check_max_stack_depth_subprog(struct bpf_verifier_env *env, int idx,
+ bool check_priv_stack, bool priv_stack_supported)
{
struct bpf_subprog_info *subprog = env->subprog_info;
struct bpf_insn *insn = env->prog->insnsi;
int depth = 0, frame = 0, i, subprog_end;
bool tail_call_reachable = false;
+ bool priv_stack_eligible = false;
int ret_insn[MAX_CALL_FRAMES];
int ret_prog[MAX_CALL_FRAMES];
- int j;
+ int j, subprog_stack_depth;
+ int orig_idx = idx;
+ if (check_priv_stack)
+ subprog[idx].subtree_top_idx = idx;
i = subprog[idx].start;
process_func:
/* protect against potential stack overflow that might happen when
@@ -6030,18 +6072,33 @@ static int check_max_stack_depth_subprog(struct bpf_verifier_env *env, int idx)
* tailcall will unwind the current stack frame but it will not get rid
* of caller's stack as shown on the example above.
*/
- if (idx && subprog[idx].has_tail_call && depth >= 256) {
+ if (!check_priv_stack && idx && subprog[idx].has_tail_call && depth >= 256) {
verbose(env,
"tail_calls are not allowed when call stack of previous frames is %d bytes. Too large\n",
depth);
return -EACCES;
}
- depth += round_up_stack_depth(env, subprog[idx].stack_depth);
- if (depth > MAX_BPF_STACK) {
+ subprog_stack_depth = round_up_stack_depth(env, subprog[idx].stack_depth);
+ depth += subprog_stack_depth;
+ if (!check_priv_stack && !priv_stack_supported && depth > MAX_BPF_STACK) {
verbose(env, "combined stack size of %d calls is %d. Too large\n",
frame + 1, depth);
return -EACCES;
}
+ if (check_priv_stack) {
+ if (subprog_stack_depth > MAX_BPF_STACK) {
+ verbose(env, "stack size of subprog %d is %d. Too large\n",
+ idx, subprog_stack_depth);
+ return -EACCES;
+ }
+
+ if (!priv_stack_eligible && depth >= BPF_PRIV_STACK_MIN_SUBTREE_SIZE) {
+ subprog[orig_idx].priv_stack_eligible = true;
+ env->prog->aux->priv_stack_eligible = priv_stack_eligible = true;
+ }
+ subprog[orig_idx].subtree_stack_depth =
+ max_t(u16, subprog[orig_idx].subtree_stack_depth, depth);
+ }
continue_func:
subprog_end = subprog[idx + 1].start;
for (; i < subprog_end; i++) {
@@ -6078,6 +6135,12 @@ static int check_max_stack_depth_subprog(struct bpf_verifier_env *env, int idx)
next_insn = i + insn[i].imm + 1;
sidx = find_subprog(env, next_insn);
if (sidx < 0) {
+ /* It is possible that callback func has been removed as dead code after
+ * instruction rewrites, e.g. bpf_loop with cnt 0.
+ */
+ if (check_priv_stack)
+ continue;
+
