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    Subject[PATCH 2/2] samples/bpf: add a test for bpf_override_return
    Date
    From: Josef Bacik <jbacik@fb.com>

    This adds a basic test for bpf_override_return to verify it works. We
    override the main function for mounting a btrfs fs so it'll return
    -ENOMEM and then make sure that trying to mount a btrfs fs will fail.

    Acked-by: Alexei Starovoitov <ast@kernel.org>
    Signed-off-by: Josef Bacik <jbacik@fb.com>
    ---
    samples/bpf/Makefile | 4 ++++
    samples/bpf/test_override_return.sh | 15 +++++++++++++++
    samples/bpf/tracex7_kern.c | 16 ++++++++++++++++
    samples/bpf/tracex7_user.c | 28 ++++++++++++++++++++++++++++
    tools/include/uapi/linux/bpf.h | 7 ++++++-
    tools/testing/selftests/bpf/bpf_helpers.h | 3 ++-
    6 files changed, 71 insertions(+), 2 deletions(-)
    create mode 100755 samples/bpf/test_override_return.sh
    create mode 100644 samples/bpf/tracex7_kern.c
    create mode 100644 samples/bpf/tracex7_user.c

    diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
    index ea2b9e6135f3..83d06bc1f710 100644
    --- a/samples/bpf/Makefile
    +++ b/samples/bpf/Makefile
    @@ -14,6 +14,7 @@ hostprogs-y += tracex3
    hostprogs-y += tracex4
    hostprogs-y += tracex5
    hostprogs-y += tracex6
    +hostprogs-y += tracex7
    hostprogs-y += test_probe_write_user
    hostprogs-y += trace_output
    hostprogs-y += lathist
    @@ -58,6 +59,7 @@ tracex3-objs := bpf_load.o $(LIBBPF) tracex3_user.o
    tracex4-objs := bpf_load.o $(LIBBPF) tracex4_user.o
    tracex5-objs := bpf_load.o $(LIBBPF) tracex5_user.o
    tracex6-objs := bpf_load.o $(LIBBPF) tracex6_user.o
    +tracex7-objs := bpf_load.o $(LIBBPF) tracex7_user.o
    load_sock_ops-objs := bpf_load.o $(LIBBPF) load_sock_ops.o
    test_probe_write_user-objs := bpf_load.o $(LIBBPF) test_probe_write_user_user.o
    trace_output-objs := bpf_load.o $(LIBBPF) trace_output_user.o
    @@ -100,6 +102,7 @@ always += tracex3_kern.o
    always += tracex4_kern.o
    always += tracex5_kern.o
    always += tracex6_kern.o
    +always += tracex7_kern.o
    always += sock_flags_kern.o
    always += test_probe_write_user_kern.o
    always += trace_output_kern.o
    @@ -153,6 +156,7 @@ HOSTLOADLIBES_tracex3 += -lelf
    HOSTLOADLIBES_tracex4 += -lelf -lrt
    HOSTLOADLIBES_tracex5 += -lelf
    HOSTLOADLIBES_tracex6 += -lelf
    +HOSTLOADLIBES_tracex7 += -lelf
    HOSTLOADLIBES_test_cgrp2_sock2 += -lelf
    HOSTLOADLIBES_load_sock_ops += -lelf
    HOSTLOADLIBES_test_probe_write_user += -lelf
    diff --git a/samples/bpf/test_override_return.sh b/samples/bpf/test_override_return.sh
    new file mode 100755
    index 000000000000..e68b9ee6814b
    --- /dev/null
    +++ b/samples/bpf/test_override_return.sh
    @@ -0,0 +1,15 @@
    +#!/bin/bash
    +
    +rm -f testfile.img
    +dd if=/dev/zero of=testfile.img bs=1M seek=1000 count=1
    +DEVICE=$(losetup --show -f testfile.img)
    +mkfs.btrfs -f $DEVICE
    +mkdir tmpmnt
    +./tracex7 $DEVICE
    +if [ $? -eq 0 ]
    +then
    + echo "SUCCESS!"
    +else
    + echo "FAILED!"
    +fi
    +losetup -d $DEVICE
    diff --git a/samples/bpf/tracex7_kern.c b/samples/bpf/tracex7_kern.c
    new file mode 100644
    index 000000000000..1ab308a43e0f
    --- /dev/null
    +++ b/samples/bpf/tracex7_kern.c
    @@ -0,0 +1,16 @@
    +#include <uapi/linux/ptrace.h>
    +#include <uapi/linux/bpf.h>
    +#include <linux/version.h>
    +#include "bpf_helpers.h"
    +
    +SEC("kprobe/open_ctree")
    +int bpf_prog1(struct pt_regs *ctx)
    +{
    + unsigned long rc = -12;
    +
    + bpf_override_return(ctx, rc);
    + return 0;
    +}
    +
    +char _license[] SEC("license") = "GPL";
    +u32 _version SEC("version") = LINUX_VERSION_CODE;
    diff --git a/samples/bpf/tracex7_user.c b/samples/bpf/tracex7_user.c
    new file mode 100644
    index 000000000000..8a52ac492e8b
    --- /dev/null
    +++ b/samples/bpf/tracex7_user.c
    @@ -0,0 +1,28 @@
    +#define _GNU_SOURCE
    +
    +#include <stdio.h>
    +#include <linux/bpf.h>
    +#include <unistd.h>
    +#include "libbpf.h"
    +#include "bpf_load.h"
    +
    +int main(int argc, char **argv)
    +{
    + FILE *f;
    + char filename[256];
    + char command[256];
    + int ret;
    +
    + snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
    +
    + if (load_bpf_file(filename)) {
    + printf("%s", bpf_log_buf);
    + return 1;
    + }
    +
    + snprintf(command, 256, "mount %s tmpmnt/", argv[1]);
    + f = popen(command, "r");
    + ret = pclose(f);
    +
    + return ret ? 0 : 1;
    +}
    diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
    index 4a4b6e78c977..3756dde69834 100644
    --- a/tools/include/uapi/linux/bpf.h
    +++ b/tools/include/uapi/linux/bpf.h
    @@ -673,6 +673,10 @@ union bpf_attr {
    * @buf: buf to fill
    * @buf_size: size of the buf
    * Return : 0 on success or negative error code
    + *
    + * int bpf_override_return(pt_regs, rc)
    + * @pt_regs: pointer to struct pt_regs
    + * @rc: the return value to set
    */
    #define __BPF_FUNC_MAPPER(FN) \
    FN(unspec), \
    @@ -732,7 +736,8 @@ union bpf_attr {
    FN(xdp_adjust_meta), \
    FN(perf_event_read_value), \
    FN(perf_prog_read_value), \
    - FN(getsockopt),
    + FN(getsockopt), \
    + FN(override_return),

    /* integer value in 'imm' field of BPF_CALL instruction selects which helper
    * function eBPF program intends to call
    diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h
    index abfa4c5c8527..086733298d5e 100644
    --- a/tools/testing/selftests/bpf/bpf_helpers.h
    +++ b/tools/testing/selftests/bpf/bpf_helpers.h
    @@ -81,7 +81,8 @@ static int (*bpf_perf_event_read_value)(void *map, unsigned long long flags,
    static int (*bpf_perf_prog_read_value)(void *ctx, void *buf,
    unsigned int buf_size) =
    (void *) BPF_FUNC_perf_prog_read_value;
    -
    +static int (*bpf_override_return)(void *ctx, unsigned long rc) =
    + (void *) BPF_FUNC_override_return;

    /* llvm builtin functions that eBPF C program may use to
    * emit BPF_LD_ABS and BPF_LD_IND instructions
    --
    2.7.5
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