[PATCH ima-evm-utils v4] Add tests for MMAP_CHECK and MMAP_CHECK_REQPROT hooks
Mimi Zohar
zohar at linux.ibm.com
Thu Feb 2 16:15:18 UTC 2023
On Thu, 2023-02-02 at 14:51 +0100, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu at huawei.com>
>
> Add tests to ensure that, after applying the kernel patch 'ima: Align
> ima_file_mmap() parameters with mmap_file LSM hook', the MMAP_CHECK hook
> checks the protections applied by the kernel and not those requested by the
> application.
>
> Also ensure that after applying 'ima: Introduce MMAP_CHECK_REQPROT hook',
> the MMAP_CHECK_REQPROT hook checks the protections requested by the
> application.
>
> Test both with the test_mmap application that by default requests the
> PROT_READ protection flag. Its syntax is:
>
> test_mmap <file> <mode>
>
> where mode can be:
> - exec: adds the PROT_EXEC protection flag to mmap()
> - read_implies_exec: calls the personality() system call with
> READ_IMPLIES_EXEC as the first argument before mmap()
> - mprotect: adds the PROT_EXEC protection flag to a memory area in addition
> to PROT_READ
> - exec_on_writable: calls mmap() with PROT_EXEC on a file which has a
> writable mapping
>
> Check the different combinations of hooks/modes and ensure that a
> measurement entry is found in the IMA measurement list only when it is
> expected. No measurement entry should be found when only the PROT_READ
> protection flag is requested or the matching policy rule has the
> MMAP_CHECK_REQPROT hook and the personality() system call was called with
> READ_IMPLIES_EXEC.
>
> mprotect() with PROT_EXEC on an existing memory area protected with
> PROT_READ should be denied (with an appraisal rule), regardless of the MMAP
> hook specified in the policy. The same applies for mmap() with PROT_EXEC on
> a file with a writable mapping.
>
> Signed-off-by: Roberto Sassu <roberto.sassu at huawei.com>
> ---
> Changelog
>
> v3:
> - Check if there are IMA policy rules without fowner= and fsuuid=, and
> if yes, skip the tests due to possible interference (suggested by Mimi)
> - Fix style issues in tests/mmap_check.test
>
> v2:
> - Distinguish setup-related errors from test-related errors in test_mmap
> - Rename key_path and key_path_der variables to g_key_path and
> g_key_path_der (suggested by Stefan)
> - Write data to the test file in check_mmap()
> - Ensure that there are no setup-related errors from test_mmap in
> tests/mmap_check.test
> - Print the found entry in the IMA measurement list (suggested by Mimi)
> - Check for errors when writing the test file in check_deny()
> - Pass TST_KEY_PATH to the new environment
> - Add description to each test (suggested by Mimi)
>
> v1:
> - Declare PATCHES and uses new expect_pass_if() and expect_fail_if()
> (suggested by Stefan)
> - Replace $FAIL with $HARDFAIL when the error occurs in the setup phase of
> the test (to not make an expect_fail test successful for other reasons
> than the focus of the test)
> - Declare local variables in one line (suggested by Stefan)
> - Print the test being executed at the beginning, so that the message
> always appears also if an error occurs
> - Print the result of the tests in a separate line and separate the output
> of each test
>
> tests/Makefile.am | 4 +-
> tests/mmap_check.test | 357 ++++++++++++++++++++++++++++++++++++++++++
> tests/test_mmap.c | 121 ++++++++++++++
> 3 files changed, 481 insertions(+), 1 deletion(-)
> create mode 100755 tests/mmap_check.test
> create mode 100644 tests/test_mmap.c
>
> diff --git a/tests/Makefile.am b/tests/Makefile.am
> index a0463b7b5b5d..ca9c4ca18380 100644
> --- a/tests/Makefile.am
> +++ b/tests/Makefile.am
> @@ -2,7 +2,9 @@ check_SCRIPTS =
> TESTS = $(check_SCRIPTS)
>
> check_SCRIPTS += ima_hash.test sign_verify.test boot_aggregate.test \
> - fsverity.test portable_signatures.test
> + fsverity.test portable_signatures.test mmap_check.test
> +
> +check_PROGRAMS := test_mmap
>
> .PHONY: check_logs
> check_logs:
> diff --git a/tests/mmap_check.test b/tests/mmap_check.test
> new file mode 100755
> index 000000000000..228c417a7f46
> --- /dev/null
> +++ b/tests/mmap_check.test
> @@ -0,0 +1,357 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Copyright (C) 2022-2023 Roberto Sassu <roberto.sassu at huawei.com>
> +#
> +# Check the behavior of MMAP_CHECK and MMAP_CHECK_REQPROT
> +
> +trap '_report_exit_and_cleanup _cleanup_env cleanup' SIGINT SIGTERM SIGSEGV EXIT
> +
> +PATCHES=(
> +'ima: Align ima_file_mmap() parameters with mmap_file LSM hook'
> +'ima: Introduce MMAP_CHECK_REQPROT hook'
> +)
> +
> +# Base VERBOSE on the environment variable, if set.
> +VERBOSE="${VERBOSE:-0}"
> +
> +# Errors defined in test_mmap
> +ERR_SETUP=1
> +ERR_TEST=2
> +
> +cd "$(dirname "$0")" || exit "$FAIL"
> +export PATH=$PWD/../src:$PWD:$PATH
> +export LD_LIBRARY_PATH=$LD_LIBRARY_PATH
> +. ./functions.sh
> +_require evmctl
> +
> +cleanup() {
> + if [ "$g_loop_mounted" = "1" ]; then
> + popd > /dev/null || exit "$FAIL"
> + umount "$g_mountpoint"
> + fi
> +
> + if [ -n "$g_dev" ]; then
> + losetup -d "$g_dev"
> + fi
> +
> + if [ -n "$g_image" ]; then
> + rm -f "$g_image"
> + fi
> +
> + if [ -n "$g_mountpoint" ]; then
> + rm -Rf "$g_mountpoint"
> + fi
> +
> + if [ -n "$g_key_path_der" ]; then
> + rm -f "$g_key_path_der"
> + fi
> +}
> +
> +# Use the fsuuid= IMA policy keyword to select only files created/used by the
> +# tests below. Also use fowner= to differentiate between files created/used by
> +# individual tests.
> +IMA_UUID="28b23254-9467-44c0-b6ba-34b12e85a26e"
> +MMAP_CHECK_FOWNER=2000
> +MMAP_CHECK_REQPROT_FOWNER=2001
> +MEASURE_MMAP_CHECK_RULE="measure func=MMAP_CHECK fsuuid=$IMA_UUID fowner=$MMAP_CHECK_FOWNER"
> +MEASURE_MMAP_CHECK_REQPROT_RULE="measure func=MMAP_CHECK_REQPROT fsuuid=$IMA_UUID fowner=$MMAP_CHECK_REQPROT_FOWNER"
> +APPRAISE_MMAP_CHECK_RULE="appraise func=MMAP_CHECK fsuuid=$IMA_UUID fowner=$MMAP_CHECK_FOWNER"
> +APPRAISE_MMAP_CHECK_REQPROT_RULE="appraise func=MMAP_CHECK_REQPROT fsuuid=$IMA_UUID fowner=$MMAP_CHECK_REQPROT_FOWNER"
> +
> +check_load_ima_rule() {
> + local rule_loaded result new_policy
> +
> + rule_loaded=$(grep "$1" /sys/kernel/security/ima/policy)
> + if [ -z "$rule_loaded" ]; then
> + new_policy=$(mktemp -p "$g_mountpoint")
> + echo "$1" > "$new_policy"
> + echo "$new_policy" > /sys/kernel/security/ima/policy
> + result=$?
> + rm -f "$new_policy"
> +
> + if [ "$result" -ne 0 ]; then
> + echo "${RED}Failed to set IMA policy${NORM}"
> + return "$HARDFAIL"
> + fi
> + fi
> +
> + return "$OK"
> +}
> +
> +check_mmap() {
> + local hook="$1"
> + local arg="$2"
> + local test_file fowner rule result test_file_entry
> +
> + echo -e "\nTest: ${FUNCNAME[0]} (hook=\"$hook\", test_mmap arg: \"$arg\")"
> +
> + if ! test_file=$(mktemp -p "$PWD"); then
> + echo "${RED}Cannot create $test_file${NORM}"
> + return "$HARDFAIL"
> + fi
> +
> + if ! echo "test" > "$test_file"; then
> + echo "${RED}Cannot write $test_file${NORM}"
> + return "$FAIL"
> + fi
> +
> + fowner="$MMAP_CHECK_FOWNER"
> + rule="$MEASURE_MMAP_CHECK_RULE"
> +
> + if [ "$hook" = "MMAP_CHECK_REQPROT" ]; then
> + fowner="$MMAP_CHECK_REQPROT_FOWNER"
> + rule="$MEASURE_MMAP_CHECK_REQPROT_RULE"
> + fi
> +
> + if ! chown "$fowner" "$test_file"; then
> + echo "${RED}Cannot change owner of $test_file${NORM}"
> + return "$HARDFAIL"
> + fi
> +
> + check_load_ima_rule "$rule"
> + result=$?
> + if [ $result -ne "$OK" ]; then
> + return $result
> + fi
> +
> + test_mmap "$test_file" "$arg"
> + result=$?
> +
> + if [ $result -ne 0 ] && [ $result -ne "$ERR_TEST" ]; then
> + echo "${RED}Unexpected exit status $result from test_mmap${NORM}"
> + return "$HARDFAIL"
> + fi
> +
> + if [ "$TFAIL" != "yes" ]; then
> + echo -n "Result (expect found): "
> + else
> + echo -n "Result (expect not found): "
> + fi
> +
> + test_file_entry=$(awk '$5 == "'"$test_file"'"' < /sys/kernel/security/ima/ascii_runtime_measurements)
> + if [ -z "$test_file_entry" ]; then
> + echo "not found"
> + return "$FAIL"
> + fi
> +
> + echo "found"
> +
> + if [ "$VERBOSE" -gt 0 ]; then
> + echo "$test_file_entry"
> + fi
> +
> + return "$OK"
> +}
> +
> +check_deny() {
> + local hook="$1"
> + local arg="$2"
> + local test_file fowner rule result
> +
> + echo -e "\nTest: ${FUNCNAME[0]} (hook=\"$hook\", test_mmap arg: \"$arg\")"
> +
> + if ! test_file=$(mktemp -p "$PWD"); then
> + echo "${RED}Cannot create $test_file${NORM}"
> + return "$HARDFAIL"
> + fi
> +
> + if ! echo "test" > "$test_file"; then
> + echo "${RED}Cannot write $test_file${NORM}"
> + return "$FAIL"
> + fi
> +
> + if ! evmctl ima_sign -a sha256 --key "$g_key_path" "$test_file" &> /dev/null; then
> + echo "${RED}Cannot sign $test_file${NORM}"
> + return "$HARDFAIL"
> + fi
> +
> + fowner="$MMAP_CHECK_FOWNER"
> + rule="$APPRAISE_MMAP_CHECK_RULE"
> +
> + if [ "$hook" = "MMAP_CHECK_REQPROT" ]; then
> + fowner="$MMAP_CHECK_REQPROT_FOWNER"
> + rule="$APPRAISE_MMAP_CHECK_REQPROT_RULE"
> + fi
> +
> + if ! chown "$fowner" "$test_file"; then
> + echo "${RED}Cannot change owner of $test_file${NORM}"
> + return "$HARDFAIL"
> + fi
> +
> + check_load_ima_rule "$rule"
> + result=$?
> + if [ $result -ne "$OK" ]; then
> + return $result
> + fi
> +
> + test_mmap "$test_file" exec
> + result=$?
> +
> + if [ $result -ne 0 ] && [ $result -ne "$ERR_TEST" ]; then
> + echo "${RED}Unexpected exit status $result from test_mmap${NORM}"
> + return "$HARDFAIL"
> + fi
> +
> + test_mmap "$test_file" "$arg"
> + result=$?
> +
> + if [ $result -ne 0 ] && [ $result -ne "$ERR_TEST" ]; then
> + echo "${RED}Unexpected exit status $result from test_mmap${NORM}"
> + return "$HARDFAIL"
> + fi
> +
> + if [ "$TFAIL" != "yes" ]; then
> + echo -n "Result (expect denied): "
> + else
> + echo -n "Result (expect allowed): "
> + fi
> +
> + if [ $result -eq 0 ]; then
> + echo "allowed"
> + return "$FAIL"
> + fi
> +
> + echo "denied"
> + return "$OK"
> +}
> +
> +# Run in the new environment if TST_ENV is set.
> +_run_env "$TST_KERNEL" "$PWD/$(basename "$0")" "TST_ENV=$TST_ENV TST_KERNEL=$TST_KERNEL PATH=$PATH LD_LIBRARY_PATH=$LD_LIBRARY_PATH VERBOSE=$VERBOSE TST_KEY_PATH=$TST_KEY_PATH"
> +
> +# Exit from the creator of the new environment.
> +_exit_env "$TST_KERNEL"
> +
> +# Mount filesystems in the new environment.
> +_init_env
> +
> +if [ "$(whoami)" != "root" ]; then
> + echo "${CYAN}This script must be executed as root${NORM}"
> + exit "$SKIP"
> +fi
> +
> +if [ ! -f /sys/kernel/security/ima/policy ]; then
> + echo "${CYAN}IMA policy file not found${NORM}"
> + exit "$SKIP"
> +fi
> +
> +if ! cat /sys/kernel/security/ima/policy &> /dev/null; then
> + echo "${CYAN}IMA policy file is not readable${NORM}"
> + exit "$SKIP"
> +fi
> +
> +if ! awk '$0 ~ /^(measure|appraise)/ && $0 !~ /fsuuid=/ && $0 !~ /fowner=/ { exit 1 }' < /sys/kernel/security/ima/policy; then
> + echo "${CYAN}IMA policy rules without fsuuid= and fowner=, cannot continue due to possible interference with the tests${NORM}"
> + exit "$SKIP
Since you're only adding mmap tests, I'd prefer the above test was
limited to "func=MMAP_CHECK".
> +fi
> +
> +if [ -n "$TST_KEY_PATH" ]; then
> + if [ "${TST_KEY_PATH:0:1}" != "/" ]; then
> + echo "${RED}Absolute path required for the signing key${NORM}"
> + exit "$FAIL"
> + fi
> +
> + if [ ! -f "$TST_KEY_PATH" ]; then
> + echo "${RED}Kernel signing key not found in $TST_KEY_PATH${NORM}"
> + exit "$FAIL"
> + fi
> +
> + g_key_path="$TST_KEY_PATH"
> +elif [ -f "$PWD/../signing_key.pem" ]; then
> + g_key_path="$PWD/../signing_key.pem"
> +elif [ -f "/lib/modules/$(uname -r)/source/certs/signing_key.pem" ]; then
> + g_key_path="/lib/modules/$(uname -r)/source/certs/signing_key.pem"
> +elif [ -f "/lib/modules/$(uname -r)/build/certs/signing_key.pem" ]; then
> + g_key_path="/lib/modules/$(uname -r)/build/certs/signing_key.pem"
> +else
> + echo "${CYAN}Kernel signing key not found${NORM}"
> + exit "$SKIP"
> +fi
> +
> +g_key_path_der=$(mktemp)
> +
> +openssl x509 -in "$g_key_path" -out "$g_key_path_der" -outform der
> +if ! keyctl padd asymmetric pubkey %keyring:.ima < "$g_key_path_der" &> /dev/null; then
> + echo "${RED}Public key cannot be added to the IMA keyring${NORM}"
> + exit "$FAIL"
> +fi
> +
> +g_mountpoint=$(mktemp -d)
> +g_image=$(mktemp)
> +
> +if [ -z "$g_mountpoint" ]; then
> + echo "${RED}Mountpoint directory not created${NORM}"
> + exit "$FAIL"
> +fi
> +
> +if ! dd if=/dev/zero of="$g_image" bs=1M count=20 &> /dev/null; then
> + echo "${RED}Cannot create test image${NORM}"
> + exit "$FAIL"
> +fi
> +
> +g_dev=$(losetup -f "$g_image" --show)
> +if [ -z "$g_dev" ]; then
> + echo "${RED}Cannot create loop device${NORM}"
> + exit "$FAIL"
> +fi
> +
> +if ! mkfs.ext4 -U "$IMA_UUID" -b 4096 "$g_dev" &> /dev/null; then
> + echo "${RED}Cannot format $g_dev${NORM}"
> + exit "$FAIL"
> +fi
> +
> +if ! mount -o i_version "$g_dev" "$g_mountpoint"; then
> + echo "${RED}Cannot mount loop device${NORM}"
> + exit "$FAIL"
> +fi
> +
> +g_loop_mounted=1
> +pushd "$g_mountpoint" > /dev/null || exit "$FAIL"
> +
> +# Ensure that IMA does not add a new measurement entry if an application calls
> +# mmap() with PROT_READ, and a policy rule contains the MMAP_CHECK hook.
> +# In this case, both the protections requested by the application and the final
> +# protections applied by the kernel contain only PROT_READ, so there is no
> +# match with the IMA rule, which expects PROT_EXEC to be set.
> +expect_fail check_mmap "MMAP_CHECK" ""
> +
> +# Ensure that IMA adds a new measurement entry if an application calls mmap()
> +# with PROT_READ | PROT_EXEC, and a policy rule contains the MMAP_CHECK hook.
> +expect_pass check_mmap "MMAP_CHECK" "exec"
> +
> +# Same as in the first test, but in this case the application calls the
> +# personality() system call with READ_IMPLIES_EXEC, which causes the kernel to
> +# add PROT_EXEC in the final protections passed to the MMAP_CHECK hook.
> +#
> +# Ensure that the bug introduced by 98de59bfe4b2 ("take calculation of final
> +# protections in security_mmap_file() into a helper") is fixed, by passing the
> +# final protections again to the MMAP_CHECK hook. Due to the bug, the hook
> +# received the protections requested by the application. Since those protections
> +# don't have PROT_EXEC, IMA was not creating a measurement entry.
> +expect_pass_if '0' check_mmap "MMAP_CHECK" "read_implies_exec"
> +
> +# Repeat the previous three tests, but with the new MMAP_CHECK_REQPROT hook,
> +# which behaves like the buggy MMAP_CHECK hook. In the third test, expect that
> +# no new measurement entry is created, since the MMAP_CHECK_REQPROT hook sees
> +# the protections requested by the application (PROT_READ).
> +expect_fail_if '1' check_mmap "MMAP_CHECK_REQPROT" ""
> +expect_pass_if '1' check_mmap "MMAP_CHECK_REQPROT" "exec"
> +expect_fail_if '1' check_mmap "MMAP_CHECK_REQPROT" "read_implies_exec"
> +
> +# Ensure that IMA refuses an mprotect() with PROT_EXEC on a memory area
> +# obtained with an mmap() with PROT_READ. This is due to the inability of IMA
> +# to measure/appraise the file for which mmap() was called (locking issue).
> +expect_pass check_deny "MMAP_CHECK" "mprotect"
> +
> +# Ensure that MMAP_CHECK_REQPROT has the same behavior of MMAP_CHECK for the
> +# previous test.
> +expect_pass_if '1' check_deny "MMAP_CHECK_REQPROT" "mprotect"
> +
> +# Ensure that there cannot be an mmap() with PROT_EXEC on a file with writable
> +# mappings, due to the inability of IMA to make a reliable measurement of that
> +# file.
> +expect_pass check_deny "MMAP_CHECK" "exec_on_writable"
> +
> +# Ensure that MMAP_CHECK_REQPROT has the same behavior of MMAP_CHECK for the
> +# previous test.
> +expect_pass_if '1' check_deny "MMAP_CHECK_REQPROT" "exec_on_writable"
> diff --git a/tests/test_mmap.c b/tests/test_mmap.c
> new file mode 100644
> index 000000000000..7106ba70fc53
> --- /dev/null
> +++ b/tests/test_mmap.c
> @@ -0,0 +1,121 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2023 Huawei Technologies Duesseldorf GmbH
> + *
> + * Tool to test IMA MMAP_CHECK and MMAP_CHECK_REQPROT hooks.
> + */
> +#include <stdio.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <sys/stat.h>
> +#include <sys/mman.h>
> +#include <sys/personality.h>
> +
> +/*
> + * Convention: return 1 for errors that should not occur, as they are
> + * setup-related, return 2 for errors that might occur due to testing
> + * conditions.
> + */
> +#define ERR_SETUP 1
> +#define ERR_TEST 2
> +
> +int main(int argc, char *argv[])
> +{
> + struct stat st;
> + void *ptr, *ptr_write = NULL;
> + int ret, fd, fd_write, prot = PROT_READ;
> +
> + if (!argv[1]) {
> + printf("Missing file parameter\n");
> + return ERR_SETUP;
> + }
> +
> + if (argv[2] && !strcmp(argv[2], "read_implies_exec")) {
> + ret = personality(READ_IMPLIES_EXEC);
> + if (ret == -1) {
> + printf("Failed to set personality, err: %d (%s)\n",
> + -errno, strerror(errno));
> + return ERR_SETUP;
> + }
> + }
> +
> + if (stat(argv[1], &st) == -1) {
> + printf("Failed to access %s, err: %d (%s)\n", argv[1], -errno,
> + strerror(errno));
> + return ERR_SETUP;
> + }
> +
> + if (argv[2] && !strcmp(argv[2], "exec_on_writable")) {
> + fd_write = open(argv[1], O_RDWR);
> + if (fd_write == -1) {
> + printf("Failed to open %s in r/w, err: %d (%s)\n",
> + argv[1], -errno, strerror(errno));
> + return ERR_SETUP;
> + }
> +
> + ptr_write = mmap(0, st.st_size, PROT_WRITE, MAP_SHARED,
> + fd_write, 0);
> + close(fd_write);
> +
> + if (ptr_write == MAP_FAILED) {
> + printf("Failed mmap() with PROT_WRITE on %s, err: %d (%s)\n",
> + argv[1], -errno, strerror(errno));
> + return ERR_SETUP;
> + }
> + }
> +
> + fd = open(argv[1], O_RDONLY);
> + if (fd == -1) {
> + printf("Failed to open %s in ro, err: %d (%s)\n", argv[1],
> + -errno, strerror(errno));
> +
> + if (ptr_write && munmap(ptr_write, st.st_size) == -1)
> + printf("Failed munmap() of writable mapping on %s, err: %d (%s)\n",
> + argv[1], -errno, strerror(errno));
> +
> + return ERR_SETUP;
> + }
> +
> + if (argv[2] && !strncmp(argv[2], "exec", 4))
> + prot |= PROT_EXEC;
> +
> + ptr = mmap(0, st.st_size, prot, MAP_PRIVATE, fd, 0);
> +
> + close(fd);
> +
> + if (ptr_write && munmap(ptr_write, st.st_size) == -1) {
> + printf("Failed munmap() of writable mapping on %s, err: %d (%s)\n",
> + argv[1], -errno, strerror(errno));
> + return ERR_SETUP;
> + }
> +
> + if (ptr == MAP_FAILED) {
> + ret = ERR_SETUP;
> + if (argv[2] && !strcmp(argv[2], "exec_on_writable") &&
> + errno == EACCES)
> + ret = ERR_TEST;
> +
FYI, on an older distro kernel, the mmap fails and results in following
without any explanation.
Test: check_mmap (hook="MMAP_CHECK", test_mmap arg: "exec")
Unexpected exit status 1 from test_mmap
With some additional debugging, I'm seeing:
Failed mmap() /tmp/tmp.4gD2UjSvC4/tmp.PlzUEm09hO, err: -13 (Permission
denied)b
Mimi
> + return ret;
> + }
> +
> + ret = 0;
> +
> + if (argv[2] && !strcmp(argv[2], "mprotect")) {
> + ret = mprotect(ptr, st.st_size, PROT_EXEC);
> + if (ret == -1) {
> + ret = ERR_SETUP;
> + if (errno == EPERM)
> + ret = ERR_TEST;
> + }
> + }
> +
> + if (munmap(ptr, st.st_size) == -1) {
> + printf("Failed munmap() of mapping on %s, err: %d (%s)\n",
> + argv[1], -errno, strerror(errno));
> + return ERR_SETUP;
> + }
> +
> + return ret;
> +}
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