cgproxy/execsnoop-kernel

Prons and cons

• use stable execve tracepoint, so build once and should work everywhere
• need to build in kernel tree

Build in kernel tree

• ready and config kernel tree

# kernel config
gunzip -c /proc/config.gz > .config
make oldconfig && make prepare
# install headers to ./usr/include
make headers_install -j8
# build bpf
make M=samples/bpf -j8

• put or link execsnoop_kern.c and execsnoop_user.c to samples/bpf/
• edit samples/bpf/makefile

# in samples/bpf/makefile
tprogs-y += execsnoop
execsnoop-objs := bpf_load.o execsnoop_user.o $(TRACE_HELPERS)
always-y += execsnoop_kern.o

Run

cd samples/bpf
sudo bash -c "ulimit -l unlimited && ./execsnoop"

Detail build command

using make V=1 M=samples/bpf | tee -a log.txt to get and filter following command

• build execsnoop_kern.o

  note -g is needed if with BPF CO-RE

clang -nostdinc \
	-isystem /usr/lib/gcc/x86_64-pc-linux-gnu/10.1.0/include \
	-I./arch/x86/include \
	-I./arch/x86/include/generated  \
	-I./include \
	-I./arch/x86/include/uapi \
	-I./arch/x86/include/generated/uapi \
	-I./include/uapi \
	-I./include/generated/uapi \
	-include ./include/linux/kconfig.h \
	-I./samples/bpf \
	-I./tools/testing/selftests/bpf/ \
	-I./tools/lib/ \
	-include asm_goto_workaround.h \
	-D__KERNEL__ -D__BPF_TRACING__ -Wno-unused-value -Wno-pointer-sign \
	-D__TARGET_ARCH_x86 -Wno-compare-distinct-pointer-types \
	-Wno-gnu-variable-sized-type-not-at-end \
	-Wno-address-of-packed-member -Wno-tautological-compare \
	-Wno-unknown-warning-option  \
	-fno-stack-protector \
	-O2 -emit-llvm -c samples/bpf/execsnoop_kern.c \
	-o - | llc -march=bpf  -filetype=obj -o samples/bpf/execsnoop_kern.o

• build execsnoop_user.o

  gcc -Wall -O2 -Wmissing-prototypes -Wstrict-prototypes \
  	-I./usr/include \
  	-I./tools/testing/selftests/bpf/ \
  	-I./tools/lib/ \
  	-I./tools/include \
  	-I./tools/perf \
  	-DHAVE_ATTR_TEST=0  \
  	-c -o samples/bpf/execsnoop_user.o samples/bpf/execsnoop_user.c

• build execsnoop

  gcc -Wall -O2 -Wmissing-prototypes -Wstrict-prototypes \
	  -I./usr/include \
	  -I./tools/testing/selftests/bpf/ \
	  -I./tools/lib/ \
	  -I./tools/include \
	  -I./tools/perf \
	  -DHAVE_ATTR_TEST=0 \
	  -o samples/bpf/execsnoop \
	  samples/bpf/bpf_load.o samples/bpf/execsnoop_user.o \
	  tools/testing/selftests/bpf/trace_helpers.o tools/lib/bpf/libbpf.a \
	  -lelf -lz

With bpftool

• gen

bpftool gen skeleton execsnoop_kern.o > execsnoop_kern_skel.h

• build

gcc -Wall -O2 execsnoop_user_1.c -o execsnoop -lbpf

Some resources

• A thorough introduction to eBPF
• Write eBPF program in pure C