Re: [PATCH RFT v3 5/5] kselftest/clone3: Test shadow stack support

[Anders Roxell <anders.roxell@linaro.org>]

On 2023-11-20 23:54, Mark Brown wrote:
> Add basic test coverage for specifying the shadow stack for a newly
> created thread via clone3(), including coverage of the newly extended
> argument structure.
>
> In order to facilitate testing on systems without userspace shadow stack
> support we manually enable shadow stacks on startup, this is architecture
> specific due to the use of an arch_prctl() on x86. Due to interactions with
> potential userspace locking of features we actually detect support for
> shadow stacks on the running system by attempting to allocate a shadow
> stack page during initialisation using map_shadow_stack(), warning if this
> succeeds when the enable failed.
>
> Signed-off-by: Mark Brown <broonie@kernel.org>
> ---
>  tools/testing/selftests/clone3/clone3.c           | 117 ++++++++++++++++++++++
>  tools/testing/selftests/clone3/clone3_selftests.h |   7 ++
>  2 files changed, 124 insertions(+)
>
> diff --git a/tools/testing/selftests/clone3/clone3.c b/tools/testing/selftests/clone3/clone3.c
> index 6adbfd14c841..0f9f99dc5aac 100644
> --- a/tools/testing/selftests/clone3/clone3.c
> +++ b/tools/testing/selftests/clone3/clone3.c
> @@ -11,6 +11,7 @@
>  #include <stdint.h>
>  #include <stdio.h>
>  #include <stdlib.h>
> +#include <sys/mman.h>
>  #include <sys/syscall.h>
>  #include <sys/types.h>
>  #include <sys/un.h>
> @@ -21,6 +22,10 @@
>  #include "../kselftest.h"
>  #include "clone3_selftests.h"
>
> +static bool shadow_stack_enabled;
> +static bool shadow_stack_supported;
> +static size_t max_supported_args_size;
> +
>  enum test_mode {
>  	CLONE3_ARGS_NO_TEST,
>  	CLONE3_ARGS_ALL_0,
> @@ -28,6 +33,7 @@ enum test_mode {
>  	CLONE3_ARGS_INVAL_EXIT_SIGNAL_NEG,
>  	CLONE3_ARGS_INVAL_EXIT_SIGNAL_CSIG,
>  	CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG,
> +	CLONE3_ARGS_SHADOW_STACK,
>  };
>
>  typedef bool (*filter_function)(void);
> @@ -44,6 +50,36 @@ struct test {
>  	filter_function filter;
>  };
>
> +#ifndef __NR_map_shadow_stack
> +#define __NR_map_shadow_stack 453
> +#endif
> +
> +/*
> + * We check for shadow stack support by attempting to use
> + * map_shadow_stack() since features may have been locked by the
> + * dynamic linker resulting in spurious errors when we attempt to
> + * enable on startup.  We warn if the enable failed.
> + */
> +static void test_shadow_stack_supported(void)
> +{
> +        long shadow_stack;
> +
> +	shadow_stack = syscall(__NR_map_shadow_stack, 0, getpagesize(), 0);
> +	if (shadow_stack == -1) {
> +		ksft_print_msg("map_shadow_stack() not supported\n");
> +	} else if ((void *)shadow_stack == MAP_FAILED) {
> +		ksft_print_msg("Failed to map shadow stack\n");
> +	} else {
> +		ksft_print_msg("Shadow stack supportd\n");
> +		shadow_stack_supported = true;
> +
> +		if (!shadow_stack_enabled)
> +			ksft_print_msg("Mapped but did not enable shadow stack\n");
> +
> +		munmap((void *)shadow_stack, getpagesize());
> +	}
> +}
> +
>  static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
>  {
>  	struct __clone_args args = {
> @@ -89,6 +125,9 @@ static int call_clone3(uint64_t flags, size_t size, enum test_mode test_mode)
>  	case CLONE3_ARGS_INVAL_EXIT_SIGNAL_NSIG:
>  		args.exit_signal = 0x00000000000000f0ULL;
>  		break;
> +	case CLONE3_ARGS_SHADOW_STACK:
> +		args.shadow_stack_size = getpagesize();
> +		break;
>  	}
>
>  	memcpy(&args_ext.args, &args, sizeof(struct __clone_args));
> @@ -179,6 +218,26 @@ static bool no_timenamespace(void)
>  	return true;
>  }
>
> +static bool have_shadow_stack(void)
> +{
> +	if (shadow_stack_supported) {
> +		ksft_print_msg("Shadow stack supported\n");
> +		return true;
> +	}
> +
> +	return false;
> +}
> +
> +static bool no_shadow_stack(void)
> +{
> +	if (!shadow_stack_supported) {
> +		ksft_print_msg("Shadow stack not supported\n");
> +		return true;
> +	}
> +
> +	return false;
> +}
> +
>  static size_t page_size_plus_8(void)
>  {
>  	return getpagesize() + 8;
> @@ -322,16 +381,74 @@ static const struct test tests[] = {
>  		.expected = -EINVAL,
>  		.test_mode = CLONE3_ARGS_NO_TEST,
>  	},
> +	{
> +		.name = "Shadow stack on system with shadow stack",
> +		.flags = CLONE_VM,
> +		.size = 0,
> +		.expected = 0,
> +		.e2big_valid = true,
> +		.test_mode = CLONE3_ARGS_SHADOW_STACK,
> +		.filter = no_shadow_stack,
> +	},
> +	{
> +		.name = "Shadow stack on system without shadow stack",
> +		.flags = CLONE_VM,
> +		.size = 0,
> +		.expected = -EINVAL,
> +		.e2big_valid = true,
> +		.test_mode = CLONE3_ARGS_SHADOW_STACK,
> +		.filter = have_shadow_stack,
> +	},
>  };
>
> +#ifdef __x86_64__
> +#define ARCH_SHSTK_ENABLE	0x5001
> +#define ARCH_SHSTK_SHSTK	(1ULL <<  0)
> +
> +#define ARCH_PRCTL(arg1, arg2)					\
> +({								\
> +	long _ret;						\
> +	register long _num  asm("eax") = __NR_arch_prctl;	\
> +	register long _arg1 asm("rdi") = (long)(arg1);		\
> +	register long _arg2 asm("rsi") = (long)(arg2);		\
> +								\
> +	asm volatile (						\
> +		"syscall\n"					\
> +		: "=a"(_ret)					\
> +		: "r"(_arg1), "r"(_arg2),			\
> +		  "0"(_num)					\
> +		: "rcx", "r11", "memory", "cc"			\
> +	);							\
> +	_ret;							\
> +})
> +
> +#define ENABLED_SHADOW_STACK
> +static inline void enable_shadow_stack(void)
> +{
> +	int ret = ARCH_PRCTL(ARCH_SHSTK_ENABLE, ARCH_SHSTK_SHSTK);
> +	if (ret == 0)
> +		shadow_stack_enabled = true;
> +}
> +
> +#endif
> +
> +#ifndef ENABLE_SHADOW_STACK

Should this be ENABLED_SHADOW_STACK ?


Built this patchset for x86 gave me this build error:

make[4]: Entering directory '/home/anders/src/kernel/linux/tools/testing/selftests/clone3'
x86_64-linux-gnu-gcc -g -std=gnu99 -isystem /home/anders/.cache/tuxmake/builds/513/build/usr/include     clone3.c -lcap -o /home/anders/.cache/tuxmake/builds/513/build/kselftest/clone3/clone
3
clone3.c:436:13: error: redefinition of 'enable_shadow_stack'
  436 | static void enable_shadow_stack(void)
      |             ^~~~~~~~~~~~~~~~~~~
clone3.c:426:20: note: previous definition of 'enable_shadow_stack' with type 'void(void)'
  426 | static inline void enable_shadow_stack(void)
      |                    ^~~~~~~~~~~~~~~~~~~
make[4]: Leaving directory '/home/anders/src/kernel/linux/tools/testing/selftests/clone3'
make[4]: *** [../lib.mk:181: /home/anders/.cache/tuxmake/builds/513/build/kselftest/clone3/clone3] Error 1
make[3]: *** [Makefile:178: all] Error 2
make[3]: Target 'install' not remade because of errors.
make[2]: *** [/home/anders/src/kernel/linux/Makefile:1362: kselftest-install] Error 2


Cheers,
Anders