[PATCH v2] rtld: Add glibc.rtld.enable_secure tunable.
Joe Simmons-Talbott
josimmon@redhat.com
Tue Jan 2 21:16:25 GMT 2024
On Tue, Dec 12, 2023 at 02:48:53PM -0500, Siddhesh Poyarekar wrote:
> 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".
Updated.
>
> > 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.
Moved this __tunables_init as you've suggested.
>
> > 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.
>
Updated as you suggested and setting enable_secure doesn't set any
tunables.
> > + }
> > }
> > /* 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.
Updated to do this in __tubables_init as you've suggested.
Thanks,
Joe
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