bpfloader - move sysctl setting from rc to binary
this allows tightening the sepolicy for 'proc_bpf' in:
https://android-review.git.corp.google.com/c/platform/system/sepolicy/+/2323635
'sepolicy - move proc bpf writes from bpfloader.rc to bpfloader binary'
While we're at it, this also allows us to actually verify
that these sysctls are being successfully set.
Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: Ibde9d817b690395e3eb12f6b5acdf3060aca67b9
diff --git a/bpfloader/BpfLoader.cpp b/bpfloader/BpfLoader.cpp
index fd261b5..c1be22a 100644
--- a/bpfloader/BpfLoader.cpp
+++ b/bpfloader/BpfLoader.cpp
@@ -235,10 +235,48 @@
}
}
+// Technically 'value' doesn't need to be newline terminated, but it's best
+// to include a newline to match 'echo "value" > /proc/sys/...foo' behaviour,
+// which is usually how kernel devs test the actual sysctl interfaces.
+int writeProcSysFile(const char *filename, const char *value) {
+ android::base::unique_fd fd(open(filename, O_WRONLY | O_CLOEXEC));
+ if (fd < 0) {
+ const int err = errno;
+ ALOGE("open('%s', O_WRONLY | O_CLOEXEC) -> %s", filename, strerror(err));
+ return -err;
+ }
+ int len = strlen(value);
+ int v = write(fd, value, len);
+ if (v < 0) {
+ const int err = errno;
+ ALOGE("write('%s', '%s', %d) -> %s", filename, value, len, strerror(err));
+ return -err;
+ }
+ if (v != len) {
+ // In practice, due to us only using this for /proc/sys/... files, this can't happen.
+ ALOGE("write('%s', '%s', %d) -> short write [%d]", filename, value, len, v);
+ return -EINVAL;
+ }
+ return 0;
+}
+
int main(int argc, char** argv) {
(void)argc;
android::base::InitLogging(argv, &android::base::KernelLogger);
+ // Linux 5.16-rc1 changed the default to 2 (disabled but changeable), but we need 0 (enabled)
+ // (this writeFile is known to fail on at least 4.19, but always defaults to 0 on pre-5.13,
+ // on 5.13+ it depends on CONFIG_BPF_UNPRIV_DEFAULT_OFF)
+ if (writeProcSysFile("/proc/sys/kernel/unprivileged_bpf_disabled", "0\n") &&
+ android::bpf::isAtLeastKernelVersion(5, 13, 0)) return 1;
+
+ // Enable the eBPF JIT -- but do note that on 64-bit kernels it is likely
+ // already force enabled by the kernel config option BPF_JIT_ALWAYS_ON
+ if (writeProcSysFile("/proc/sys/net/core/bpf_jit_enable", "1\n")) return 1;
+
+ // Enable JIT kallsyms export for privileged users only
+ if (writeProcSysFile("/proc/sys/net/core/bpf_jit_kallsyms", "1\n")) return 1;
+
// This is ugly... but this allows InProcessTethering which runs as system_server,
// instead of as network_stack to access /sys/fs/bpf/tethering, which would otherwise
// (due to genfscon rules) have fs_bpf_tethering selinux context, which is restricted
diff --git a/bpfloader/bpfloader.rc b/bpfloader/bpfloader.rc
index 1d6248e..b1a6bdb 100644
--- a/bpfloader/bpfloader.rc
+++ b/bpfloader/bpfloader.rc
@@ -15,14 +15,6 @@
# considered to have booted successfully.
#
on load_bpf_programs
- # Linux 5.16-rc1 has changed the default to 2 (disabled but changeable),
- # but we need 0
- write /proc/sys/kernel/unprivileged_bpf_disabled 0
- # Enable the eBPF JIT -- but do note that on 64-bit kernels it is likely
- # already force enabled by the kernel config option BPF_JIT_ALWAYS_ON
- write /proc/sys/net/core/bpf_jit_enable 1
- # Enable JIT kallsyms export for privileged users only
- write /proc/sys/net/core/bpf_jit_kallsyms 1
exec_start bpfloader
service bpfloader /system/bin/bpfloader
