From: Jiri Olsa <jolsa@xxxxxxxxxx> [ Upstream commit 861de02e5f3f2a104eecc5af1d248cb7bf8c5f75 ] Currently module can be unloaded even if there's a trampoline register in it. It's easily reproduced by running in parallel: # while :; do ./test_progs -t module_attach; done # while :; do rmmod bpf_testmod; sleep 0.5; done Taking the module reference in case the trampoline's ip is within the module code. Releasing it when the trampoline's ip is unregistered. Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx> Link: https://lore.kernel.org/bpf/20210326105900.151466-1-jolsa@xxxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- include/linux/bpf.h | 2 ++ kernel/bpf/trampoline.c | 30 ++++++++++++++++++++++++++++++ 2 files changed, 32 insertions(+) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 564ebf91793e..88b581b75d5b 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -41,6 +41,7 @@ struct bpf_local_storage; struct bpf_local_storage_map; struct kobject; struct mem_cgroup; +struct module; extern struct idr btf_idr; extern spinlock_t btf_idr_lock; @@ -630,6 +631,7 @@ struct bpf_trampoline { /* Executable image of trampoline */ struct bpf_tramp_image *cur_image; u64 selector; + struct module *mod; }; struct bpf_attach_target_info { diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index 986dabc3d11f..a431d7af884c 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -9,6 +9,7 @@ #include <linux/btf.h> #include <linux/rcupdate_trace.h> #include <linux/rcupdate_wait.h> +#include <linux/module.h> /* dummy _ops. The verifier will operate on target program's ops. */ const struct bpf_verifier_ops bpf_extension_verifier_ops = { @@ -87,6 +88,26 @@ out: return tr; } +static int bpf_trampoline_module_get(struct bpf_trampoline *tr) +{ + struct module *mod; + int err = 0; + + preempt_disable(); + mod = __module_text_address((unsigned long) tr->func.addr); + if (mod && !try_module_get(mod)) + err = -ENOENT; + preempt_enable(); + tr->mod = mod; + return err; +} + +static void bpf_trampoline_module_put(struct bpf_trampoline *tr) +{ + module_put(tr->mod); + tr->mod = NULL; +} + static int is_ftrace_location(void *ip) { long addr; @@ -108,6 +129,9 @@ static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr) ret = unregister_ftrace_direct((long)ip, (long)old_addr); else ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL); + + if (!ret) + bpf_trampoline_module_put(tr); return ret; } @@ -134,10 +158,16 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr) return ret; tr->func.ftrace_managed = ret; + if (bpf_trampoline_module_get(tr)) + return -ENOENT; + if (tr->func.ftrace_managed) ret = register_ftrace_direct((long)ip, (long)new_addr); else ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, NULL, new_addr); + + if (ret) + bpf_trampoline_module_put(tr); return ret; } -- 2.30.2
