101 lines
2.6 KiB
C
101 lines
2.6 KiB
C
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// SPDX-License-Identifier: GPL-2.0
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#include <vmlinux.h>
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#include <bpf/bpf_helpers.h>
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#include <bpf/bpf_tracing.h>
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const volatile struct {
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/* thread to activate trace programs for */
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pid_t tgid;
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/* return error from __init function */
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int inject_error;
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/* uffd monitored range start address */
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void *fault_addr;
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} bpf_mod_race_config = { -1 };
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int bpf_blocking = 0;
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int res_try_get_module = -1;
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static __always_inline bool check_thread_id(void)
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{
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struct task_struct *task = bpf_get_current_task_btf();
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return task->tgid == bpf_mod_race_config.tgid;
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}
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/* The trace of execution is something like this:
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*
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* finit_module()
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* load_module()
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* prepare_coming_module()
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* notifier_call(MODULE_STATE_COMING)
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* btf_parse_module()
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* btf_alloc_id() // Visible to userspace at this point
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* list_add(btf_mod->list, &btf_modules)
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* do_init_module()
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* freeinit = kmalloc()
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* ret = mod->init()
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* bpf_prog_widen_race()
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* bpf_copy_from_user()
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* ...<sleep>...
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* if (ret < 0)
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* ...
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* free_module()
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* return ret
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*
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* At this point, module loading thread is blocked, we now load the program:
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*
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* bpf_check
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* add_kfunc_call/check_pseudo_btf_id
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* btf_try_get_module
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* try_get_module_live == false
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* return -ENXIO
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*
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* Without the fix (try_get_module_live in btf_try_get_module):
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*
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* bpf_check
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* add_kfunc_call/check_pseudo_btf_id
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* btf_try_get_module
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* try_get_module == true
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* <store module reference in btf_kfunc_tab or used_btf array>
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* ...
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* return fd
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*
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* Now, if we inject an error in the blocked program, our module will be freed
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* (going straight from MODULE_STATE_COMING to MODULE_STATE_GOING).
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* Later, when bpf program is freed, it will try to module_put already freed
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* module. This is why try_get_module_live returns false if mod->state is not
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* MODULE_STATE_LIVE.
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*/
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SEC("fmod_ret.s/bpf_fentry_test1")
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int BPF_PROG(widen_race, int a, int ret)
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{
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char dst;
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if (!check_thread_id())
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return 0;
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/* Indicate that we will attempt to block */
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bpf_blocking = 1;
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bpf_copy_from_user(&dst, 1, bpf_mod_race_config.fault_addr);
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return bpf_mod_race_config.inject_error;
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}
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SEC("fexit/do_init_module")
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int BPF_PROG(fexit_init_module, struct module *mod, int ret)
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{
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if (!check_thread_id())
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return 0;
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/* Indicate that we finished blocking */
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bpf_blocking = 2;
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return 0;
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}
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SEC("fexit/btf_try_get_module")
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int BPF_PROG(fexit_module_get, const struct btf *btf, struct module *mod)
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{
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res_try_get_module = !!mod;
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return 0;
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}
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char _license[] SEC("license") = "GPL";
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