[PATCH v2] rtld: Add glibc.rtld.enable_secure tunable.
Siddhesh Poyarekar
siddhesh@gotplt.org
Tue Dec 12 19:48:53 GMT 2023
On 2023-12-05 12:45, Joe Simmons-Talbott wrote:
> Add a tunable for setting __libc_enable_secure to 1. Does not set
> __libc_enable_secure to 0 if the tunable is set to 0. Ignores any
> tunables following glib.rtld.enable_secure. One use-case for this
> addition is to enable testing code paths that depend on
> __libc_eanble_secure being set without the need to use setxid binaries.
> ---
> Changes to v1:
> * handle the tunable for the dynamic loader as well.
>
> NOTE: I'm not certain I've picked the appropriate place to handle
> glibc.rtld.enable_secure. I tried to make it happen as early as
> possible to minimize and places where __libc_enable_secure might be
> checked before the tunable initialization takes place.
>
> NEWS | 4 +
> csu/libc-start.c | 4 +
> elf/Makefile | 2 +
> elf/dl-tunables.c | 8 +-
> elf/dl-tunables.h | 11 +++
> elf/dl-tunables.list | 6 ++
> elf/tst-rtld-list-tunables.exp | 1 +
> elf/tst-tunables-enable_secure.c | 115 ++++++++++++++++++++++++++++
> sysdeps/unix/sysv/linux/dl-sysdep.c | 3 +
> 9 files changed, 153 insertions(+), 1 deletion(-)
> create mode 100644 elf/tst-tunables-enable_secure.c
>
> diff --git a/NEWS b/NEWS
> index 8c1c149f91..b04fb15064 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -43,6 +43,10 @@ Major new features:
> on thread stack created by pthread_create or memory allocated by
> malloc).
>
> +* A new tunable, glibc.rtld.enable_secure, used to set __libc_enable_secure
> + to 1. Setting the tunable to 0 does *NOT* set __libc_enable_secure to 0.
> + Once the tunable is encountered all following tunables are ignored.
> +
__libc_enable_secure is an internal detail. How about rephrasing it in
terms of the feature this implements, i.e. "A new tunable, ... used to
run a program as if it were a setuid process, enabling a number of
security features. This is currently a testing tool to allow more
extensive verification tests for AT_SECURE programs and not meant to be
a security feature".
> Deprecated and removed features, and other changes affecting compatibility:
>
> * The ldconfig program now skips file names containing ';' or ending in
> diff --git a/csu/libc-start.c b/csu/libc-start.c
> index c3bb6d09bc..2f546a3677 100644
> --- a/csu/libc-start.c
> +++ b/csu/libc-start.c
> @@ -266,6 +266,10 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
>
> __tunables_init (__environ);
>
> + int32_t tes = TUNABLE_GET_FULL (glibc, rtld, enable_secure, int32_t, NULL);
> + if (tes == 1)
> + __libc_enable_secure = 1;
> +
OK, but I wonder if it's easier to just do this in __tunables_init so
that it's done in a single place.
> ARCH_INIT_CPU_FEATURES ();
>
> /* Do static pie self relocation after tunables and cpu features
> diff --git a/elf/Makefile b/elf/Makefile
> index afec7be084..6c38a72b0d 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -285,6 +285,7 @@ tests-static-internal := \
> tst-tls1-static \
> tst-tls1-static-non-pie \
> tst-tunables \
> + tst-tunables-enable_secure \
> # tests-static-internal
>
> CRT-tst-tls1-static-non-pie := $(csu-objpfx)crt1.o
> @@ -2672,6 +2673,7 @@ $(objpfx)tst-glibc-hwcaps-mask.out: \
> $(objpfx)tst-glibc-hwcaps-cache.out: $(objpfx)tst-glibc-hwcaps
>
> tst-tunables-ARGS = -- $(host-test-program-cmd)
> +tst-tunables-enable_secure-ARGS = -- $(host-test-program-cmd)
>
> $(objpfx)list-tunables.out: tst-rtld-list-tunables.sh $(objpfx)ld.so
> $(SHELL) $< $(objpfx)ld.so '$(test-wrapper-env)' \
> diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
> index 644d21d1b0..d6c55cfaf2 100644
> --- a/elf/dl-tunables.c
> +++ b/elf/dl-tunables.c
> @@ -250,7 +250,13 @@ parse_tunables (char *valstring)
> }
>
> for (int i = 0; i < ntunables; i++)
> - tunable_initialize (tunables[i].t, tunables[i].value);
> + {
> + tunable_initialize (tunables[i].t, tunables[i].value);
> +
> + /* Ignore all tunables after encountering "glibc.rtld.enable_secure" */
> + if (tunable_strcmp(tunables[i].t->name, "glibc.rtld.enable_secure") == 0)
> + break;
This still has the problem that Szabolcs pointed out, i.e. one only
needs to reorder tunables to be before enable_secure to avoid being
ignored. What you need to do is when you encounter enable_secure in
parse_tunable_string (look for the tunable_is_name call in there), you
return 0. That will ensure that no tunables are set at all and you've
successfully emulated setxid for tunables. If you set
__libc_enable_secure there, all code that follows will run as if the
program were AT_SECURE.
> + }
> }
>
> /* Initialize the tunables list from the environment. For now we only use the
> diff --git a/elf/dl-tunables.h b/elf/dl-tunables.h
> index 0df4dde24e..2d4fc84d74 100644
> --- a/elf/dl-tunables.h
> +++ b/elf/dl-tunables.h
> @@ -164,4 +164,15 @@ tunable_is_name (const char *orig, const char *envname)
> return false;
> }
>
> +/* Compare two strings. */
> +static __always_inline int
> +tunable_strcmp (const char *left, const char *right)
> +{
> + for (;*left != '\0' && *right != '\0'; right++, left++)
> + if (*left != *right)
> + break;
> +
> + return *left - *right;
> +}
> +
> #endif
> diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
> index 1b23fc9473..cb1b35854e 100644
> --- a/elf/dl-tunables.list
> +++ b/elf/dl-tunables.list
> @@ -136,6 +136,12 @@ glibc {
> minval: 0
> default: 512
> }
> + enable_secure {
> + type: INT_32
> + minval: 0
> + maxval: 1
> + default: 0
> + }
> }
>
> mem {
> diff --git a/elf/tst-rtld-list-tunables.exp b/elf/tst-rtld-list-tunables.exp
> index 2233ea9c7c..db0e1c86e9 100644
> --- a/elf/tst-rtld-list-tunables.exp
> +++ b/elf/tst-rtld-list-tunables.exp
> @@ -12,5 +12,6 @@ glibc.malloc.tcache_unsorted_limit: 0x0 (min: 0x0, max: 0x[f]+)
> glibc.malloc.top_pad: 0x20000 (min: 0x0, max: 0x[f]+)
> glibc.malloc.trim_threshold: 0x0 (min: 0x0, max: 0x[f]+)
> glibc.rtld.dynamic_sort: 2 (min: 1, max: 2)
> +glibc.rtld.enable_secure: 0 (min: 0, max: 1)
> glibc.rtld.nns: 0x4 (min: 0x1, max: 0x10)
> glibc.rtld.optional_static_tls: 0x200 (min: 0x0, max: 0x[f]+)
> diff --git a/elf/tst-tunables-enable_secure.c b/elf/tst-tunables-enable_secure.c
> new file mode 100644
> index 0000000000..e749ec9f17
> --- /dev/null
> +++ b/elf/tst-tunables-enable_secure.c
> @@ -0,0 +1,115 @@
> +/* Check GLIBC_TUNABLES parsing for enable_secure.
> + Copyright (C) 2023 Free Software Foundation, Inc.
> + This file is part of the GNU C Library.
> +
> + The GNU C Library is free software; you can redistribute it and/or
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +#include <array_length.h>
> +#include <dl-tunables.h>
> +#include <getopt.h>
> +#include <intprops.h>
> +#include <stdint.h>
> +#include <stdlib.h>
> +#include <support/capture_subprocess.h>
> +#include <support/check.h>
> +#include <sys/auxv.h>
> +#include <unistd.h>
> +
> +static int restart;
> +#define CMDLINE_OPTIONS \
> + { "restart", no_argument, &restart, 1 },
> +
> +static const struct test_t
> +{
> + const char *env;
> + int32_t expected_malloc_check;
> + int32_t expected_enable_secure;
> +} tests[] =
> +{
> + /* Expected tunable format. */
> + {
> + "glibc.malloc.check=2:glibc.rtld.enable_secure=1",
> + 2,
> + 1,
> + },
> + /* Tunables encountered after enable_secure should be ignored. */
> + {
> + "glibc.rtld.enable_secure=1:glibc.malloc.check=2",
> + 0,
> + 1,
> + },
> +};
> +
> +static int
> +handle_restart (int i)
> +{
> + TEST_COMPARE (tests[i].expected_malloc_check,
> + TUNABLE_GET_FULL (glibc, malloc, check, int32_t, NULL));
> + TEST_COMPARE (tests[i].expected_enable_secure,
> + TUNABLE_GET_FULL (glibc, rtld, enable_secure, int32_t, NULL));
> + if (tests[i].expected_enable_secure == 1)
> + {
> + TEST_COMPARE (1, __libc_enable_secure);
> + }
> + return 0;
> +}
> +
> +static int
> +do_test (int argc, char *argv[])
> +{
> + /* We must have either:
> + - One or four parameters left if called initially:
> + + path to ld.so optional
> + + "--library-path" optional
> + + the library path optional
> + + the application name
> + + the test to check */
> +
> + TEST_VERIFY_EXIT (argc == 2 || argc == 5);
> +
> + if (restart)
> + return handle_restart (atoi (argv[1]));
> +
> + char nteststr[INT_BUFSIZE_BOUND (int)];
> +
> + char *spargv[10];
> + {
> + int i = 0;
> + for (; i < argc - 1; i++)
> + spargv[i] = argv[i + 1];
> + spargv[i++] = (char *) "--direct";
> + spargv[i++] = (char *) "--restart";
> + spargv[i++] = nteststr;
> + spargv[i] = NULL;
> + }
> +
> + for (int i = 0; i < array_length (tests); i++)
> + {
> + snprintf (nteststr, sizeof nteststr, "%d", i);
> +
> + printf ("[%d] Spawned test for %s\n", i, tests[i].env);
> + setenv ("GLIBC_TUNABLES", tests[i].env, 1);
> + struct support_capture_subprocess result
> + = support_capture_subprogram (spargv[0], spargv);
> + support_capture_subprocess_check (&result, "tst-tunables-enable_secure",
> + 0, sc_allow_stderr);
> + support_capture_subprocess_free (&result);
> + }
> +
> + return 0;
> +}
> +
> +#define TEST_FUNCTION_ARGV do_test
> +#include <support/test-driver.c>
> diff --git a/sysdeps/unix/sysv/linux/dl-sysdep.c b/sysdeps/unix/sysv/linux/dl-sysdep.c
> index 1b3dd869b5..d3a30e8d7a 100644
> --- a/sysdeps/unix/sysv/linux/dl-sysdep.c
> +++ b/sysdeps/unix/sysv/linux/dl-sysdep.c
> @@ -108,6 +108,9 @@ _dl_sysdep_start (void **start_argptr,
> dl_hwcap_check ();
>
> __tunables_init (_environ);
> + int32_t tes = TUNABLE_GET_FULL (glibc, rtld, enable_secure, int32_t, NULL);
> + if (tes == 1)
> + __libc_enable_secure = 1;
OK, but maybe better to just do it in __tunables_init. Any specific
reason why you're doing it here? For example, you've missed the hurd
dl-sysdep change.
>
> /* Initialize DSO sorting algorithm after tunables. */
> _dl_sort_maps_init ();
Thanks,
Sid
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