[PATCH bpf-next 1/9] bpf: Remove prog->active check for bpf_lsm and bpf_iter

Martin KaFai Lau
2022-10-25T18:46:12Z

The commit 64696c40d03c ("bpf: Add __bpf_prog_{enter,exit}_struct_ops for struct_ops trampoline")
removed prog->active check for struct_ops prog. The bpf_lsm
and bpf_iter is also using trampoline. Like struct_ops, the bpf_lsm
and bpf_iter have fixed hooks for the prog to attach. The
kernel does not call the same hook in a recursive way.
This patch also removes the prog->active check for
bpf_lsm and bpf_iter.

A later patch has a test to reproduce the recursion issue
for a sleepable bpf_lsm program.

This patch appends the '_recur' naming to the existing
enter and exit functions that track the prog->active counter.
New __bpf_prog_{enter,exit}[_sleepable] function are
added to skip the prog->active tracking. The '_struct_ops'
version is also removed.

It also moves the decision on picking the enter and exit function to
the new bpf_trampoline_{enter,exit}(). It returns the '_recur' ones
for all tracing progs to use. For bpf_lsm, bpf_iter,
struct_ops (no prog->active tracking after 64696c40d03c), and
bpf_lsm_cgroup (no prog->active tracking after 69fd337a975c7),
it will return the functions that don't track the prog->active.

Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
---
arch/arm64/net/bpf_jit_comp.c | 9 +---
arch/x86/net/bpf_jit_comp.c | 19 +--------
include/linux/bpf.h | 24 +++++------
include/linux/bpf_verifier.h | 15 ++++++-
kernel/bpf/syscall.c | 5 ++-
kernel/bpf/trampoline.c | 80 +++++++++++++++++++++++++++++------
6 files changed, 98 insertions(+), 54 deletions(-)

diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
index 30f76178608b..62f805f427b7 100644
--- a/arch/arm64/net/bpf_jit_comp.c
+++ b/arch/arm64/net/bpf_jit_comp.c
@@ -1649,13 +1649,8 @@ static void invoke_bpf_prog(struct jit_ctx *ctx, struct bpf_tramp_link *l,
struct bpf_prog *p = l->link.prog;
int cookie_off = offsetof(struct bpf_tramp_run_ctx, bpf_cookie);

- if (p->aux->sleepable) {
- enter_prog = (u64)__bpf_prog_enter_sleepable;
- exit_prog = (u64)__bpf_prog_exit_sleepable;
- } else {
- enter_prog = (u64)__bpf_prog_enter;
- exit_prog = (u64)__bpf_prog_exit;
- }
+ enter_prog = (u64)bpf_trampoline_enter(p);
+ exit_prog = (u64)bpf_trampoline_exit(p);

if (l->cookie == 0) {
/* if cookie is zero, one instruction is enough to store it */
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index d7dd8e0db8da..36ffe67ad6e5 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1894,10 +1894,6 @@ static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog,
struct bpf_tramp_link *l, int stack_size,
int run_ctx_off, bool save_ret)
{
- void (*exit)(struct bpf_prog *prog, u64 start,
- struct bpf_tramp_run_ctx *run_ctx) = __bpf_prog_exit;
- u64 (*enter)(struct bpf_prog *prog,
- struct bpf_tramp_run_ctx *run_ctx) = __bpf_prog_enter;
u8 *prog = *pprog;
u8 *jmp_insn;
int ctx_cookie_off = offsetof(struct bpf_tramp_run_ctx, bpf_cookie);
@@ -1916,23 +1912,12 @@ static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog,
*/
emit_stx(&prog, BPF_DW, BPF_REG_FP, BPF_REG_1, -run_ctx_off + ctx_cookie_off);

- if (p->aux->sleepable) {
- enter = __bpf_prog_enter_sleepable;
- exit = __bpf_prog_exit_sleepable;
- } else if (p->type == BPF_PROG_TYPE_STRUCT_OPS) {
- enter = __bpf_prog_enter_struct_ops;
- exit = __bpf_prog_exit_struct_ops;
- } else if (p->expected_attach_type == BPF_LSM_CGROUP) {
- enter = __bpf_prog_enter_lsm_cgroup;
- exit = __bpf_prog_exit_lsm_cgroup;
- }
-
/* arg1: mov rdi, progs[i] */
emit_mov_imm64(&prog, BPF_REG_1, (long) p >> 32, (u32) (long) p);
/* arg2: lea rsi, [rbp - ctx_cookie_off] */
EMIT4(0x48, 0x8D, 0x75, -run_ctx_off);

- if (emit_call(&prog, enter, prog))
+ if (emit_call(&prog, bpf_trampoline_enter(p), prog))
return -EINVAL;
/* remember prog start time returned by __bpf_prog_enter */
emit_mov_reg(&prog, true, BPF_REG_6, BPF_REG_0);
@@ -1977,7 +1962,7 @@ static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog,
emit_mov_reg(&prog, true, BPF_REG_2, BPF_REG_6);
/* arg3: lea rdx, [rbp - run_ctx_off] */
EMIT4(0x48, 0x8D, 0x55, -run_ctx_off);
- if (emit_call(&prog, exit, prog))
+ if (emit_call(&prog, bpf_trampoline_exit(p), prog))
return -EINVAL;

*pprog = prog;
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 9e7d46d16032..1279e699dc98 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -854,22 +854,18 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *tr, void *image, void *i
const struct btf_func_model *m, u32 flags,
struct bpf_tramp_links *tlinks,
void *orig_call);
-/* these two functions are called from generated trampoline */
-u64 notrace __bpf_prog_enter(struct bpf_prog *prog, struct bpf_tramp_run_ctx *run_ctx);
-void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start, struct bpf_tramp_run_ctx *run_ctx);
-u64 notrace __bpf_prog_enter_sleepable(struct bpf_prog *prog, struct bpf_tramp_run_ctx *run_ctx);
-void notrace __bpf_prog_exit_sleepable(struct bpf_prog *prog, u64 start,
- struct bpf_tramp_run_ctx *run_ctx);
-u64 notrace __bpf_prog_enter_lsm_cgroup(struct bpf_prog *prog,
- struct bpf_tramp_run_ctx *run_ctx);
-void notrace __bpf_prog_exit_lsm_cgroup(struct bpf_prog *prog, u64 start,
- struct bpf_tramp_run_ctx *run_ctx);
-u64 notrace __bpf_prog_enter_struct_ops(struct bpf_prog *prog,
- struct bpf_tramp_run_ctx *run_ctx);
-void notrace __bpf_prog_exit_struct_ops(struct bpf_prog *prog, u64 start,
- struct bpf_tramp_run_ctx *run_ctx);
+u64 notrace __bpf_prog_enter_sleepable_recur(struct bpf_prog *prog,
+ struct bpf_tramp_run_ctx *run_ctx);
+void notrace __bpf_prog_exit_sleepable_recur(struct bpf_prog *prog, u64 start,
+ struct bpf_tramp_run_ctx *run_ctx);
void notrace __bpf_tramp_enter(struct bpf_tramp_image *tr);
void notrace __bpf_tramp_exit(struct bpf_tramp_image *tr);
+typedef u64 (*bpf_trampoline_enter_t)(struct bpf_prog *prog,
+ struct bpf_tramp_run_ctx *run_ctx);
+typedef void (*bpf_trampoline_exit_t)(struct bpf_prog *prog, u64 start,
+ struct bpf_tramp_run_ctx *run_ctx);
+bpf_trampoline_enter_t bpf_trampoline_enter(const struct bpf_prog *prog);
+bpf_trampoline_exit_t bpf_trampoline_exit(const struct bpf_prog *prog);

struct bpf_ksym {
unsigned long start;
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 9e1e6965f407..1a32baa78ce2 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -642,10 +642,23 @@ static inline u32 type_flag(u32 type)
}

/* only use after check_attach_btf_id() */
-static inline enum bpf_prog_type resolve_prog_type(struct bpf_prog *prog)
+static inline enum bpf_prog_type resolve_prog_type(const struct bpf_prog *prog)
{
return prog->type == BPF_PROG_TYPE_EXT ?
prog->aux->dst_prog->type : prog->type;
}

+static inline bool bpf_prog_check_recur(const struct bpf_prog *prog)
+{
+ switch (resolve_prog_type(prog)) {
+ case BPF_PROG_TYPE_TRACING:
+ return prog->expected_attach_type != BPF_TRACE_ITER;
+ case BPF_PROG_TYPE_STRUCT_OPS:
+ case BPF_PROG_TYPE_LSM:
+ return false;
+ default:
+ return true;
+ }
+}
+
#endif /* _LINUX_BPF_VERIFIER_H */
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 7b373a5e861f..a0b4266196a8 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -5133,13 +5133,14 @@ int kern_sys_bpf(int cmd, union bpf_attr *attr, unsigned int size)

run_ctx.bpf_cookie = 0;
run_ctx.saved_run_ctx = NULL;
- if (!__bpf_prog_enter_sleepable(prog, &run_ctx)) {
+ if (!__bpf_prog_enter_sleepable_recur(prog, &run_ctx)) {
/* recursion detected */
bpf_prog_put(prog);
return -EBUSY;
}
attr->test.retval = bpf_prog_run(prog, (void *) (long) attr->test.ctx_in);
- __bpf_prog_exit_sleepable(prog, 0 /* bpf_prog_run does runtime stats */, &run_ctx);
+ __bpf_prog_exit_sleepable_recur(prog, 0 /* bpf_prog_run does runtime stats */,
+ &run_ctx);
bpf_prog_put(prog);
return 0;
#endif
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index bf0906e1e2b9..d6395215b849 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -864,7 +864,7 @@ static __always_inline u64 notrace bpf_prog_start_time(void)
* [2..MAX_U64] - execute bpf prog and record execution time.
* This is start time.
*/
-u64 notrace __bpf_prog_enter(struct bpf_prog *prog, struct bpf_tramp_run_ctx *run_ctx)
+static u64 notrace __bpf_prog_enter_recur(struct bpf_prog *prog, struct bpf_tramp_run_ctx *run_ctx)
__acquires(RCU)
{
rcu_read_lock();
@@ -901,7 +901,8 @@ static void notrace update_prog_stats(struct bpf_prog *prog,
}
}

-void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start, struct bpf_tramp_run_ctx *run_ctx)
+static void notrace __bpf_prog_exit_recur(struct bpf_prog *prog, u64 start,
+ struct bpf_tramp_run_ctx *run_ctx)
__releases(RCU)
{
bpf_reset_run_ctx(run_ctx->saved_run_ctx);
@@ -912,8 +913,8 @@ void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start, struct bpf_tramp_
rcu_read_unlock();
}

-u64 notrace __bpf_prog_enter_lsm_cgroup(struct bpf_prog *prog,
- struct bpf_tramp_run_ctx *run_ctx)
+static u64 notrace __bpf_prog_enter_lsm_cgroup(struct bpf_prog *prog,
+ struct bpf_tramp_run_ctx *run_ctx)
__acquires(RCU)
{
/* Runtime stats are exported via actual BPF_LSM_CGROUP
@@ -927,8 +928,8 @@ u64 notrace __bpf_prog_enter_lsm_cgroup(struct bpf_prog *prog,
return NO_START_TIME;
}

-void notrace __bpf_prog_exit_lsm_cgroup(struct bpf_prog *prog, u64 start,
- struct bpf_tramp_run_ctx *run_ctx)
+static void notrace __bpf_prog_exit_lsm_cgroup(struct bpf_prog *prog, u64 start,
+ struct bpf_tramp_run_ctx *run_ctx)
__releases(RCU)
{
bpf_reset_run_ctx(run_ctx->saved_run_ctx);
@@ -937,7 +938,8 @@ void notrace __bpf_prog_exit_lsm_cgroup(struct bpf_prog *prog, u64 start,
rcu_read_unlock();
}

-u64 notrace __bpf_prog_enter_sleepable(struct bpf_prog *prog, struct bpf_tramp_run_ctx *run_ctx)
+u64 notrace __bpf_prog_enter_sleepable_recur(struct bpf_prog *prog,
+ struct bpf_tramp_run_ctx *run_ctx)
{
rcu_read_lock_trace();
migrate_disable();
@@ -953,8 +955,8 @@ u64 notrace __bpf_prog_enter_sleepable(struct bpf_prog *prog, struct bpf_tramp_r
return bpf_prog_start_time();
}

-void notrace __bpf_prog_exit_sleepable(struct bpf_prog *prog, u64 start,
- struct bpf_tramp_run_ctx *run_ctx)
+void notrace __bpf_prog_exit_sleepable_recur(struct bpf_prog *prog, u64 start,
+ struct bpf_tramp_run_ctx *run_ctx)
{
bpf_reset_run_ctx(run_ctx->saved_run_ctx);

@@ -964,8 +966,30 @@ void notrace __bpf_prog_exit_sleepable(struct bpf_prog *prog, u64 start,
rcu_read_unlock_trace();
}

-u64 notrace __bpf_prog_enter_struct_ops(struct bpf_prog *prog,
- struct bpf_tramp_run_ctx *run_ctx)
+static u64 notrace __bpf_prog_enter_sleepable(struct bpf_prog *prog,
+ struct bpf_tramp_run_ctx *run_ctx)
+{
+ rcu_read_lock_trace();
+ migrate_disable();
+ might_fault();
+
+ run_ctx->saved_run_ctx = bpf_set_run_ctx(&run_ctx->run_ctx);
+
+ return bpf_prog_start_time();
+}
+
+static void notrace __bpf_prog_exit_sleepable(struct bpf_prog *prog, u64 start,
+ struct bpf_tramp_run_ctx *run_ctx)
+{
+ bpf_reset_run_ctx(run_ctx->saved_run_ctx);
+
+ update_prog_stats(prog, start);
+ migrate_enable();
+ rcu_read_unlock_trace();
+}
+
+static u64 notrace __bpf_prog_enter(struct bpf_prog *prog,
+ struct bpf_tramp_run_ctx *run_ctx)
__acquires(RCU)
{
rcu_read_lock();
@@ -976,8 +1000,8 @@ u64 notrace __bpf_prog_enter_struct_ops(struct bpf_prog *prog,
return bpf_prog_start_time();
}

-void notrace __bpf_prog_exit_struct_ops(struct bpf_prog *prog, u64 start,
- struct bpf_tramp_run_ctx *run_ctx)
+static void notrace __bpf_prog_exit(struct bpf_prog *prog, u64 start,
+ struct bpf_tramp_run_ctx *run_ctx)
__releases(RCU)
{
bpf_reset_run_ctx(run_ctx->saved_run_ctx);
@@ -997,6 +1021,36 @@ void notrace __bpf_tramp_exit(struct bpf_tramp_image *tr)
percpu_ref_put(&tr->pcref);
}

+bpf_trampoline_enter_t bpf_trampoline_enter(const struct bpf_prog *prog)
+{
+ bool sleepable = prog->aux->sleepable;
+
+ if (bpf_prog_check_recur(prog))
+ return sleepable ? __bpf_prog_enter_sleepable_recur :
+ __bpf_prog_enter_recur;
+
+ if (resolve_prog_type(prog) == BPF_PROG_TYPE_LSM &&
+ prog->expected_attach_type == BPF_LSM_CGROUP)
+ return __bpf_prog_enter_lsm_cgroup;
+
+ return sleepable ? __bpf_prog_enter_sleepable : __bpf_prog_enter;
+}
+
+bpf_trampoline_exit_t bpf_trampoline_exit(const struct bpf_prog *prog)
+{
+ bool sleepable = prog->aux->sleepable;
+
+ if (bpf_prog_check_recur(prog))
+ return sleepable ? __bpf_prog_exit_sleepable_recur :
+ __bpf_prog_exit_recur;
+
+ if (resolve_prog_type(prog) == BPF_PROG_TYPE_LSM &&
+ prog->expected_attach_type == BPF_LSM_CGROUP)
+ return __bpf_prog_exit_lsm_cgroup;
+
+ return sleepable ? __bpf_prog_exit_sleepable : __bpf_prog_exit;
+}
+
int __weak
arch_prepare_bpf_trampoline(struct bpf_tramp_image *tr, void *image, void *image_end,
const struct btf_func_model *m, u32 flags,
--
2.30.2