Add selftest cases that validate bpftool's expected behavior when accessing maps protected from modification via security_bpf_map.

The test includes a BPF program attached to security_bpf_map with two maps: - A protected map that only allows read-only access - An unprotected map that allows full access

The test script attaches the BPF program to security_bpf_map and verifies that for the bpftool map command: - Read access works on both maps - Write access fails on the protected map - Write access succeeds on the unprotected map - These behaviors remain consistent when the maps are pinned

Signed-off-by: Slava Imameev slava.imameev@crowdstrike.com --- Changes in v2: - fix for a test compilation error: "conflicting types for 'bpf_fentry_test1'" Changes in v3: - Addressed review feedback - Added tests for map iterator, map and map-of-maps creation, deletion - Cleaned up excessive output logging --- --- tools/testing/selftests/bpf/Makefile | 1 + .../selftests/bpf/progs/bpf_iter_map_elem.c | 22 ++ .../selftests/bpf/progs/security_bpf_map.c | 69 ++++ .../testing/selftests/bpf/test_bpftool_map.sh | 363 ++++++++++++++++++ 4 files changed, 455 insertions(+) create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_map_elem.c create mode 100644 tools/testing/selftests/bpf/progs/security_bpf_map.c create mode 100755 tools/testing/selftests/bpf/test_bpftool_map.sh

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index cf5ed3bee573..731a86407799 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -109,6 +109,7 @@ TEST_PROGS := test_kmod.sh \ test_xdping.sh \ test_bpftool_build.sh \ test_bpftool.sh \ + test_bpftool_map.sh \ test_bpftool_metadata.sh \ test_doc_build.sh \ test_xsk.sh \ diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_map_elem.c b/tools/testing/selftests/bpf/progs/bpf_iter_map_elem.c new file mode 100644 index 000000000000..2f20485e0de3 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/bpf_iter_map_elem.c @@ -0,0 +1,22 @@ +// SPDX-License-Identifier: GPL-2.0-only + +#include "vmlinux.h" +#include <bpf/bpf_tracing.h> +#include <bpf/bpf_helpers.h> + +char _license[] SEC("license") = "GPL"; + +__u32 value_sum = 0; + +SEC("iter/bpf_map_elem") +int dump_bpf_map_values(struct bpf_iter__bpf_map_elem *ctx) +{ + __u32 value = 0; + + if (ctx->value == (void *)0) + return 0; + + bpf_probe_read_kernel(&value, sizeof(value), ctx->value); + value_sum += value; + return 0; +} diff --git a/tools/testing/selftests/bpf/progs/security_bpf_map.c b/tools/testing/selftests/bpf/progs/security_bpf_map.c new file mode 100644 index 000000000000..7176f8468641 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/security_bpf_map.c @@ -0,0 +1,69 @@ +// SPDX-License-Identifier: GPL-2.0-only + +#include "vmlinux.h" +#include <bpf/bpf_tracing.h> +#include <bpf/bpf_helpers.h> + +char _license[] SEC("license") = "GPL"; + +#define EPERM 1 /* Operation not permitted */ + +/* From include/linux/mm.h. */ +#define FMODE_WRITE 0x2 + +struct map; + +struct { + __uint(type, BPF_MAP_TYPE_ARRAY); + __type(key, __u32); + __type(value, __u32); + __uint(max_entries, 1); +} prot_status_map SEC(".maps"); + +struct { + __uint(type, BPF_MAP_TYPE_HASH); + __type(key, __u32); + __type(value, __u32); + __uint(max_entries, 3); +} prot_map SEC(".maps"); + +struct { + __uint(type, BPF_MAP_TYPE_HASH); + __type(key, __u32); + __type(value, __u32); + __uint(max_entries, 3); +} not_prot_map SEC(".maps"); + +SEC("fmod_ret/security_bpf_map") +int BPF_PROG(fmod_bpf_map, struct bpf_map *map, int fmode) +{ + __u32 key = 0; + __u32 *status_ptr = bpf_map_lookup_elem(&prot_status_map, &key); + if (!status_ptr || !*status_ptr) { + return 0; + } + + if (map == &prot_map) { + /* Allow read-only access */ + if (fmode & FMODE_WRITE) + return -EPERM; + } + + return 0; +} + +/* + * This program keeps references to maps. This is needed to prevent + * optimizing them out. + */ +SEC("fentry/bpf_fentry_test1") +int BPF_PROG(fentry_dummy1, int a) +{ + __u32 key = 0; + __u32 val1 = a; + __u32 val2 = a + 1; + + bpf_map_update_elem(&prot_map, &key, &val1, BPF_ANY); + bpf_map_update_elem(&not_prot_map, &key, &val2, BPF_ANY); + return 0; +} diff --git a/tools/testing/selftests/bpf/test_bpftool_map.sh b/tools/testing/selftests/bpf/test_bpftool_map.sh new file mode 100755 index 000000000000..383e4df08f93 --- /dev/null +++ b/tools/testing/selftests/bpf/test_bpftool_map.sh @@ -0,0 +1,363 @@ +#!/bin/sh +# SPDX-License-Identifier: GPL-2.0 + +# Kselftest framework requirement - SKIP code is 4. +ksft_skip=4 + +TESTNAME="bpftool_map" +BPF_FILE="security_bpf_map.bpf.o" +BPF_ITER_FILE="bpf_iter_map_elem.bpf.o" +PROTECTED_MAP_NAME="prot_map" +NOT_PROTECTED_MAP_NAME="not_prot_map" +BPF_FS_TMP_PARENT="/tmp" +BPF_FS_PARENT=$(awk '$3 == "bpf" {print $2; exit}' /proc/mounts) +BPF_FS_PARENT=${BPF_FS_PARENT:-$BPF_FS_TMP_PARENT} +# bpftool will mount bpf file system under BPF_DIR if it is not mounted +# under BPF_FS_PARENT. +BPF_DIR="$BPF_FS_PARENT/test_$TESTNAME" +SCRIPT_DIR=$(dirname $(realpath "$0")) +BPF_FILE_PATH="$SCRIPT_DIR/$BPF_FILE" +BPF_ITER_FILE_PATH="$SCRIPT_DIR/$BPF_ITER_FILE" +BPFTOOL_PATH="bpftool" +# Assume the script is located under tools/testing/selftests/bpf/ +KDIR_ROOT_DIR=$(realpath "$SCRIPT_DIR"/../../../../) + +_cleanup() +{ + set +eu + + # If BPF_DIR is a mount point this will not remove the mount point itself. + [ -d "$BPF_DIR" ] && rm -rf "$BPF_DIR" 2> /dev/null + + # Unmount if BPF filesystem was temporarily created. + if [ "$BPF_FS_PARENT" = "$BPF_FS_TMP_PARENT" ]; then + # A loop and recursive unmount are required as bpftool might + # create multiple mounts. For example, a bind mount of the directory + # to itself. The bind mount is created to change mount propagation + # flags on an actual mount point. + max_attempts=3 + attempt=0 + while mountpoint -q "$BPF_DIR" && [ $attempt -lt $max_attempts ]; do + umount -R "$BPF_DIR" 2>/dev/null + attempt=$((attempt+1)) + done + + # The directory still exists. Remove it now. + [ -d "$BPF_DIR" ] && rm -rf "$BPF_DIR" 2>/dev/null + fi +} + +cleanup_skip() +{ + echo "selftests: $TESTNAME [SKIP]" + _cleanup + + exit $ksft_skip +} + +cleanup() +{ + if [ "$?" = 0 ]; then + echo "selftests: $TESTNAME [PASS]" + else + echo "selftests: $TESTNAME [FAILED]" + fi + _cleanup +} + +check_root_privileges() { + if [ $(id -u) -ne 0 ]; then + echo "Need root privileges" + exit $ksft_skip + fi +} + +# Function to verify bpftool path. +# Parameters: +# $1: bpftool path +verify_bpftool_path() { + local bpftool_path="$1" + if ! "$bpftool_path" version > /dev/null 2>&1; then + echo "Could not run test without bpftool" + exit $ksft_skip + fi +} + +# Function to initialize map entries with keys [0..2] and values set to 0. +# Parameters: +# $1: Map name +# $2: bpftool path +initialize_map_entries() { + local map_name="$1" + local bpftool_path="$2" + + for key in 0 1 2; do + "$bpftool_path" map update name "$map_name" key $key 0 0 0 value 0 0 0 $key + done +} + +# Test read access to the map. +# Parameters: +# $1: Name command (name/pinned) +# $2: Map name +# $3: bpftool path +# $4: key +access_for_read() { + local name_cmd="$1" + local map_name="$2" + local bpftool_path="$3" + local key="$4" + + # Test read access to the map. + if ! "$bpftool_path" map lookup "$name_cmd" "$map_name" key $key 1>/dev/null; then + echo " Read access to $key in $map_name failed" + exit 1 + fi +} + +# Test write access to the map. +# Parameters: +# $1: Name command (name/pinned) +# $2: Map name +# $3: bpftool path +# $4: key +# $5: Whether write should succeed (true/false) +access_for_write() { + local name_cmd="$1" + local map_name="$2" + local bpftool_path="$3" + local key="$4" + local write_should_succeed="$5" + local value="1 1 1 1" + + if "$bpftool_path" map update "$name_cmd" "$map_name" key $key value $value 2>/dev/null; then + if [ "$write_should_succeed" = "false" ]; then + echo " Write access to $key in $map_name succeeded but should have failed" + exit 1 + fi + else + if [ "$write_should_succeed" = "true" ]; then + echo " Write access to $key in $map_name failed but should have succeeded" + exit 1 + fi + fi +} + +# Test entry deletion for the map. +# Parameters: +# $1: Name command (name/pinned) +# $2: Map name +# $3: bpftool path +# $4: key +# $5: Whether write should succeed (true/false) +access_for_deletion() { + local name_cmd="$1" + local map_name="$2" + local bpftool_path="$3" + local key="$4" + local write_should_succeed="$5" + local value="1 1 1 1" + + # Test deletion by key for the map. + # Before deleting, check the key exists. + if ! "$bpftool_path" map lookup "$name_cmd" "$map_name" key $key 1>/dev/null; then + echo " Key $key does not exist in $map_name" + exit 1 + fi + + # Delete by key. + if "$bpftool_path" map delete "$name_cmd" "$map_name" key $key 2>/dev/null; then + if [ "$write_should_succeed" = "false" ]; then + echo " Deletion for $key in $map_name succeeded but should have failed" + exit 1 + fi + else + if [ "$write_should_succeed" = "true" ]; then + echo " Deletion for $key in $map_name failed but should have succeeded" + exit 1 + fi + fi + + # After deleting, check the entry existence according to the expected status. + if "$bpftool_path" map lookup "$name_cmd" "$map_name" key $key 1>/dev/null; then + if [ "$write_should_succeed" = "true" ]; then + echo " Key $key for $map_name was not deleted but should have been deleted" + exit 1 + fi + else + if [ "$write_should_succeed" = "false" ]; then + echo " Key $key for $map_name was deleted but should have not been deleted" + exit 1 + fi + fi + + # Test creation of map's deleted entry, if deletion was successfull. + # Otherwise, the entry exists. + if "$bpftool_path" map update "$name_cmd" "$map_name" key $key value $value 2>/dev/null; then + if [ "$write_should_succeed" = "false" ]; then + echo " Write access to $key in $map_name succeeded after deletion attempt but should have failed" + exit 1 + fi + else + if [ "$write_should_succeed" = "true" ]; then + echo " Write access to $key in $map_name failed after deletion attempt but should have succeeded" + exit 1 + fi + fi +} + +# Test map elements iterator. +# Parameters: +# $1: Name command (name/pinned) +# $2: Map name +# $3: bpftool path +# $4: BPF_DIR +# $5: bpf iterator object file path +iterate_map_elem() { + local name_cmd="$1" + local map_name="$2" + local bpftool_path="$3" + local bpf_dir="$4" + local bpf_file="$5" + local pin_path="$bpf_dir/map_iterator" + + "$bpftool_path" iter pin "$bpf_file" "$pin_path" map "$name_cmd" "$map_name" + if [ ! -f "$pin_path" ]; then + echo " Failed to pin iterator to $pin_path" + exit 1 + fi + + cat "$pin_path" 1>/dev/null + rm "$pin_path" 2>/dev/null +} + +# Function to test map access with configurable write expectations +# Parameters: +# $1: Name command (name/pinned) +# $2: Map name +# $3: bpftool path +# $4: key for rw +# $5: key to delete +# $6: Whether write should succeed (true/false) +# $7: BPF_DIR +# $8: bpf iterator object file path +access_map() { + local name_cmd="$1" + local map_name="$2" + local bpftool_path="$3" + local key_for_rw="$4" + local key_to_del="$5" + local write_should_succeed="$6" + local bpf_dir="$7" + local bpf_iter_file_path="$8" + + access_for_read "$name_cmd" "$map_name" "$bpftool_path" "$key_for_rw" + access_for_write "$name_cmd" "$map_name" "$bpftool_path" "$key_for_rw" \ + "$write_should_succeed" + access_for_deletion "$name_cmd" "$map_name" "$bpftool_path" "$key_to_del" \ + "$write_should_succeed" + iterate_map_elem "$name_cmd" "$map_name" "$bpftool_path" "$bpf_dir" \ + "$bpf_iter_file_path" +} + +# Function to test map access with configurable write expectations +# Parameters: +# $1: Map name +# $2: bpftool path +# $3: BPF_DIR +# $4: Whether write should succeed (true/false) +# $5: bpf iterator object file path +test_map_access() { + local map_name="$1" + local bpftool_path="$2" + local bpf_dir="$3" + local pin_path="$bpf_dir/${map_name}_pinned" + local write_should_succeed="$4" + local bpf_iter_file_path="$5" + + # Test access to the map by name. + access_map "name" "$map_name" "$bpftool_path" "0 0 0 0" "1 0 0 0" \ + "$write_should_succeed" "$bpf_dir" "$bpf_iter_file_path" + + # Pin the map to the BPF filesystem + "$bpftool_path" map pin name "$map_name" "$pin_path" + if [ ! -e "$pin_path" ]; then + echo " Failed to pin $map_name" + exit 1 + fi + + # Test access to the pinned map. + access_map "pinned" "$pin_path" "$bpftool_path" "0 0 0 0" "2 0 0 0" \ + "$write_should_succeed" "$bpf_dir" "$bpf_iter_file_path" +} + +# Function to test map creation and map-of-maps +# Parameters: +# $1: bpftool path +# $2: BPF_DIR +test_map_creation_and_map_of_maps() { + local bpftool_path="$1" + local bpf_dir="$2" + local outer_map_name="outer_map_tt" + local inner_map_name="inner_map_tt" + + "$bpftool_path" map create "$bpf_dir/$inner_map_name" type array key 4 \ + value 4 entries 4 name "$inner_map_name" + if [ ! -f "$bpf_dir/$inner_map_name" ]; then + echo " Failed to create inner map file at $bpf_dir/$outer_map_name" + return 1 + fi + + "$bpftool_path" map create "$bpf_dir/$outer_map_name" type hash_of_maps \ + key 4 value 4 entries 2 name "$outer_map_name" inner_map name "$inner_map_name" + if [ ! -f "$bpf_dir/$outer_map_name" ]; then + echo " Failed to create outer map file at $bpf_dir/$outer_map_name" + return 1 + fi + + # Add entries to the outer map by name and by pinned path. + "$bpftool_path" map update pinned "$bpf_dir/$outer_map_name" key 0 0 0 0 \ + value pinned "$bpf_dir/$inner_map_name" + "$bpftool_path" map update name "$outer_map_name" key 1 0 0 0 value \ + name "$inner_map_name" + + # The outer map should be full by now. + # The following map update command is expected to fail. + if "$bpftool_path" map update name "$outer_map_name" key 2 0 0 0 value name \ + "$inner_map_name" 2>/dev/null; then + echo " Update for $outer_map_name succeeded but should have failed" + exit 1 + fi +} + +set -eu + +trap cleanup_skip EXIT + +check_root_privileges + +verify_bpftool_path "$BPFTOOL_PATH" + +trap cleanup EXIT + +# Load and attach the BPF programs to control maps access. +"$BPFTOOL_PATH" prog loadall "$BPF_FILE_PATH" "$BPF_DIR" autoattach + +initialize_map_entries "$PROTECTED_MAP_NAME" "$BPFTOOL_PATH" +initialize_map_entries "$NOT_PROTECTED_MAP_NAME" "$BPFTOOL_PATH" + +# Activate the map protection mechanism. Protection status is controlled +# by a value stored in the prot_status_map at index 0. +"$BPFTOOL_PATH" map update name prot_status_map key 0 0 0 0 value 1 0 0 0 + +# Test protected map (write should fail). +test_map_access "$PROTECTED_MAP_NAME" "$BPFTOOL_PATH" "$BPF_DIR" "false" \ + "$BPF_ITER_FILE_PATH" + +# Test not protected map (write should succeed). +test_map_access "$NOT_PROTECTED_MAP_NAME" "$BPFTOOL_PATH" "$BPF_DIR" "true" \ + "$BPF_ITER_FILE_PATH" + +test_map_creation_and_map_of_maps "$BPFTOOL_PATH" "$BPF_DIR" + +exit 0

2025-06-12 08:18 UTC+1000 ~ Slava Imameev slava.imameev@crowdstrike.com

Modify several functions in tools/bpf/bpftool/common.c to allow specification of requested access for file descriptors, such as read-only access.

Update bpftool to request only read access for maps when write access is not required. This fixes errors when reading from maps that are protected from modification via security_bpf_map.

Signed-off-by: Slava Imameev slava.imameev@crowdstrike.com

Changes in v2:

• fix for a test compilation error: "conflicting types for 'bpf_fentry_test1'"

Changes in v3:

• Addressed review feedback
• Converted the check for flags to an assert in map_parse_fds
• Modified map_fd_by_name to keep an existing fd where possible
• Fixed requested access for map delete command in do_delete
• Changed requested access to RDONLY for inner map fd in do_create
• Changed requested access to RDONLY for iterator fd in do_pin

---

---

tools/bpf/bpftool/btf.c | 3 +- tools/bpf/bpftool/common.c | 58 ++++++++++++++++++++++--------- tools/bpf/bpftool/iter.c | 2 +- tools/bpf/bpftool/link.c | 2 +- tools/bpf/bpftool/main.h | 13 ++++--- tools/bpf/bpftool/map.c | 56 +++++++++++++++++------------ tools/bpf/bpftool/map_perf_ring.c | 3 +- tools/bpf/bpftool/prog.c | 4 +-- 8 files changed, 91 insertions(+), 50 deletions(-)

diff --git a/tools/bpf/bpftool/btf.c b/tools/bpf/bpftool/btf.c index 6b14cbfa58aa..1ba27cb03348 100644 --- a/tools/bpf/bpftool/btf.c +++ b/tools/bpf/bpftool/btf.c @@ -905,7 +905,8 @@ static int do_dump(int argc, char **argv) return -1; }

• fd = map_parse_fd_and_info(&argc, &argv, &info, &len);
  

• fd = map_parse_fd_and_info(&argc, &argv, &info, &len,
  

• 			   BPF_F_RDONLY);
  

  if (fd < 0) return -1;

diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c index ecfa790adc13..3bdc65112c0d 100644 --- a/tools/bpf/bpftool/common.c +++ b/tools/bpf/bpftool/common.c

[...]

@@ -1023,8 +1042,13 @@ static int map_fd_by_name(char *name, int **fds) return -1; } -int map_parse_fds(int *argc, char ***argv, int **fds) +int map_parse_fds(int *argc, char ***argv, int **fds, __u32 open_flags) {

• LIBBPF_OPTS(bpf_get_fd_by_id_opts, opts);
• assert((open_flags & ~BPF_F_RDONLY) == 0);

Can you please "#include <assert.h>" at the top of the file? We don't need it in the kernel repo, because the header is included from tools/include/linux/kernel.h (from bpftool's main.h) if I remember correctly. But the GitHub mirror uses a stripped-down version of kernel.h which doesn't pull assert.h, so we need to include it explicitly - I just remembered when seeing your v3, sorry.

Looks good to me otherwise, thanks! Quentin