Re: [PATCH bpf] bpf: Take module reference for ip in module code
From: Alexei Starovoitov <hidden>
Date: 2021-03-24 01:23:21
Also in:
bpf
On Tue, Mar 23, 2021 at 10:15:33PM +0100, Jiri Olsa wrote:
quoted hunk ↗ jump to hunk
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 ./test_progs -t fentry_test; 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> --- kernel/bpf/trampoline.c | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+)diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index 1f3a4be4b175..f6cb179842b2 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c@@ -87,6 +87,27 @@ static struct bpf_trampoline *bpf_trampoline_lookup(u64 key) return tr; } +static struct module *ip_module_get(unsigned long ip) +{ + struct module *mod; + int err = 0; + + preempt_disable(); + mod = __module_text_address(ip); + if (mod && !try_module_get(mod)) + err = -ENOENT; + preempt_enable(); + return err ? ERR_PTR(err) : mod; +} + +static void ip_module_put(unsigned long ip) +{ + struct module *mod = __module_text_address(ip);
Conceptually looks correct, but how did you test it?! Just doing your reproducer: while :; do ./test_progs -t module_attach; done & while :; do ./test_progs -t fentry_test; done I immediately hit: [ 19.461162] WARNING: CPU: 1 PID: 232 at kernel/module.c:264 module_assert_mutex_or_preempt+0x2e/0x40 [ 19.477126] Call Trace: [ 19.477464] __module_address+0x28/0xf0 [ 19.477865] ? __bpf_trace_bpf_testmod_test_write_bare+0x10/0x10 [bpf_testmod] [ 19.478711] __module_text_address+0xe/0x60 [ 19.479156] bpf_trampoline_update+0x2ff/0x470 Which points to an obvious bug above. How did you debug it to this module going away issue? Why does test_progs -t fentry_test help to repro? Or does it? It doesn't touch anything in modules.
+ + if (mod) + module_put(mod);