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override clock_adjtime() with eBPF instead of ld.so.preload
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,21 @@ | ||
| CFLAGS ?= -O2 -Wall -pedantic | ||
| CLANG ?= clang | ||
| LLVM_STRIP ?= llvm-strip | ||
| LIBS = $(shell pkg-config --libs libbpf) | ||
| PREFIX = /usr/local | ||
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| rtclock: rtclock.c rtclock.skel.h | ||
| $(CC) $(CFLAGS) -o $@ $< $(LIBS) | ||
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| rtclock.skel.h: rtclock.bpf.o | ||
| bpftool gen skeleton $< > $@ | ||
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| rtclock.bpf.o: rtclock.bpf.c | ||
| $(CLANG) -g -O2 -Wall -target bpf -D__KERNEL__ -c $< -o $@ | ||
| $(LLVM_STRIP) -g $@ | ||
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| install: rtclock | ||
| install -D -m 755 $< $(DESTDIR)$(PREFIX)/bin/$< | ||
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| clean: | ||
| rm -f rtclock rtclock.skel.h rtclock.bpf.o |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,3 @@ | ||
| rtclock prevents connman from changing the hardware clock using eBPF, to prevent conflicts with other OSs running on the same machine that may save time in UTC rather than local time. | ||
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| When connman's clock_adjtime() calls get intercepted by rtclock, clock synchronization over NTP only sets the software clock. /etc/rc.d/rc.sysinit is responsible for synchronizing the software clock with RTC at boot time, so if RTC is set correctly (by another OS), the software clock will show the correct time even before network is ready. |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,7 @@ | ||
| download() { | ||
| : | ||
| } | ||
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| build() { | ||
| make install | ||
| } |
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,22 @@ | ||
| #include <vmlinux.h> | ||
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| #include <bpf/bpf_core_read.h> | ||
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| #define STA_UNSYNC 0x0040 | ||
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| char LICENSE[] SEC("license") = "GPL"; | ||
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| SEC("tracepoint/syscalls/sys_enter_clock_adjtime") | ||
| int override_clock_adjtime(struct trace_event_raw_sys_enter *ctx) | ||
| { | ||
| struct __kernel_timex ktx; | ||
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| if (bpf_probe_read_user(&ktx, sizeof(ktx), (void *)ctx->args[1]) < 0) { | ||
| return 0; | ||
| } | ||
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| ktx.status |= STA_UNSYNC; | ||
| bpf_probe_write_user((void *)ctx->args[1], &ktx, sizeof(ktx)); | ||
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| return 0; | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,31 @@ | ||
| #include <signal.h> | ||
| #include <stdlib.h> | ||
| #include <bpf/libbpf.h> | ||
| #include <unistd.h> | ||
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| #include "rtclock.skel.h" | ||
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| int main(int argc, char *argv[]) | ||
| { | ||
| sigset_t set; | ||
| struct rtclock_bpf *skel; | ||
| int sig; | ||
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| if (sigemptyset(&set) < 0 || sigaddset(&set, SIGTERM) < 0 || sigaddset(&set, SIGINT) < 0 || sigprocmask(SIG_BLOCK, &set, NULL) < 0) return EXIT_FAILURE; | ||
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| libbpf_set_strict_mode(LIBBPF_STRICT_ALL); | ||
| libbpf_set_print(NULL); | ||
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| if (!(skel = rtclock_bpf__open_and_load())) return EXIT_FAILURE; | ||
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| if (rtclock_bpf__attach(skel)) { | ||
| rtclock_bpf__destroy(skel); | ||
| return EXIT_FAILURE; | ||
| } | ||
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| daemon(0, 0); | ||
| sigwait(&set, &sig); | ||
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| rtclock_bpf__destroy(skel); | ||
| return EXIT_FAILURE; | ||
| } |
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