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authorAlexei Starovoitov <ast@plumgrid.com>2015-05-19 16:59:05 -0700
committerDavid S. Miller <davem@davemloft.net>2015-05-21 17:07:59 -0400
commit5bacd7805ab4f07a69c7ef4b1d45ce553d2b1c3a (patch)
tree6e2b12a280e4431e2a5c3d971a8d3ebad4c0b5bc /samples/bpf/tracex5_user.c
parentb52f00e6a7154308a08d0a2edab621f277801a2c (diff)
downloadlinux-5bacd7805ab4f07a69c7ef4b1d45ce553d2b1c3a.tar.bz2
samples/bpf: bpf_tail_call example for tracing
kprobe example that demonstrates how future seccomp programs may look like. It attaches to seccomp_phase1() function and tail-calls other BPF programs depending on syscall number. Existing optimized classic BPF seccomp programs generated by Chrome look like: if (sd.nr < 121) { if (sd.nr < 57) { if (sd.nr < 22) { if (sd.nr < 7) { if (sd.nr < 4) { if (sd.nr < 1) { check sys_read } else { if (sd.nr < 3) { check sys_write and sys_open } else { check sys_close } } } else { } else { } else { } else { } else { } the future seccomp using native eBPF may look like: bpf_tail_call(&sd, &syscall_jmp_table, sd.nr); which is simpler, faster and leaves more room for per-syscall checks. Usage: $ sudo ./tracex5 <...>-366 [001] d... 4.870033: : read(fd=1, buf=00007f6d5bebf000, size=771) <...>-369 [003] d... 4.870066: : mmap <...>-369 [003] d... 4.870077: : syscall=110 (one of get/set uid/pid/gid) <...>-369 [003] d... 4.870089: : syscall=107 (one of get/set uid/pid/gid) sh-369 [000] d... 4.891740: : read(fd=0, buf=00000000023d1000, size=512) sh-369 [000] d... 4.891747: : write(fd=1, buf=00000000023d3000, size=512) sh-369 [000] d... 4.891747: : read(fd=1, buf=00000000023d3000, size=512) Signed-off-by: Alexei Starovoitov <ast@plumgrid.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'samples/bpf/tracex5_user.c')
-rw-r--r--samples/bpf/tracex5_user.c46
1 files changed, 46 insertions, 0 deletions
diff --git a/samples/bpf/tracex5_user.c b/samples/bpf/tracex5_user.c
new file mode 100644
index 000000000000..a04dd3cd4358
--- /dev/null
+++ b/samples/bpf/tracex5_user.c
@@ -0,0 +1,46 @@
+#include <stdio.h>
+#include <linux/bpf.h>
+#include <unistd.h>
+#include <linux/filter.h>
+#include <linux/seccomp.h>
+#include <sys/prctl.h>
+#include "libbpf.h"
+#include "bpf_load.h"
+
+/* install fake seccomp program to enable seccomp code path inside the kernel,
+ * so that our kprobe attached to seccomp_phase1() can be triggered
+ */
+static void install_accept_all_seccomp(void)
+{
+ struct sock_filter filter[] = {
+ BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
+ };
+ struct sock_fprog prog = {
+ .len = (unsigned short)(sizeof(filter)/sizeof(filter[0])),
+ .filter = filter,
+ };
+ if (prctl(PR_SET_SECCOMP, 2, &prog))
+ perror("prctl");
+}
+
+int main(int ac, char **argv)
+{
+ FILE *f;
+ char filename[256];
+
+ snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+
+ if (load_bpf_file(filename)) {
+ printf("%s", bpf_log_buf);
+ return 1;
+ }
+
+ install_accept_all_seccomp();
+
+ f = popen("dd if=/dev/zero of=/dev/null count=5", "r");
+ (void) f;
+
+ read_trace_pipe();
+
+ return 0;
+}