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bpf: Take module reference for trampoline in module

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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@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210326105900.151466-1-jolsa@kernel.org
This commit is contained in:
Jiri Olsa 2021-03-26 11:59:00 +01:00 committed by Alexei Starovoitov
parent d6fe1cf890
commit 861de02e5f
2 changed files with 32 additions and 0 deletions
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2
include/linux/bpf.h
View File

@ -40,6 +40,7 @@ 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;
@ -623,6 +624,7 @@ struct bpf_trampoline {
/* Executable image of trampoline */
struct bpf_tramp_image *cur_image;
u64 selector;
struct module *mod;
};
struct bpf_attach_target_info {

30
kernel/bpf/trampoline.c
View File

@ -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;
}