Re: [PATCH 5/5] commands: add stacksmash command for causing stack overflows

[Thorsten Scherer <T.Scherer@eckelmann.de>]

Hi Ahmad,

On Mon, Sep 11, 2023 at 05:09:00PM +0200, Ahmad Fatoum wrote:
> Now that we have two mechanisms for detecting stack overflows, add a
> command to intentionally trigger stack frame and stack region overflow
> to verify their correct operation.
> 
> Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
> ---
>  commands/Kconfig      |  6 +++++
>  commands/Makefile     |  1 +
>  commands/stacksmash.c | 58 +++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 65 insertions(+)
>  create mode 100644 commands/stacksmash.c
> 
> diff --git a/commands/Kconfig b/commands/Kconfig
> index eb95b2a5fbcc..c1bba22443e6 100644
> --- a/commands/Kconfig
> +++ b/commands/Kconfig
> @@ -2401,6 +2401,12 @@ config CMD_UBSAN
>  	  This is a test command for the undefined behavior sanitizer.
>  	  It triggers various undefined behavior, and detect it.
>  
> +config CMD_STACKSMASH
> +	tristate "stacksmash"
> +	help
> +	  This commands trashes the stack to test stackprotector and
> +	  guard page. This command does not return.
> +
>  # end Miscellaneous commands
>  endmenu
>  
> diff --git a/commands/Makefile b/commands/Makefile
> index 4b083a852d83..4924755500e3 100644
> --- a/commands/Makefile
> +++ b/commands/Makefile
> @@ -145,5 +145,6 @@ obj-$(CONFIG_CMD_BTHREAD)	+= bthread.o
>  obj-$(CONFIG_CMD_UBSAN)		+= ubsan.o
>  obj-$(CONFIG_CMD_SELFTEST)	+= selftest.o
>  obj-$(CONFIG_CMD_TUTORIAL)	+= tutorial.o
> +obj-$(CONFIG_CMD_STACKSMASH)	+= stacksmash.o
>  
>  UBSAN_SANITIZE_ubsan.o := y
> diff --git a/commands/stacksmash.c b/commands/stacksmash.c
> new file mode 100644
> index 000000000000..1e9be0d40e15
> --- /dev/null
> +++ b/commands/stacksmash.c
> @@ -0,0 +1,58 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#include <common.h>
> +#include <command.h>
> +#include <complete.h>
> +#include <linux/compiler.h>
> +#include <string.h>
> +
> +static noinline void stack_overflow_frame(void)
> +{
> +	volatile int length = 512;
> +	char a[128] = {};
> +
> +	/*
> +	 * In order to avoid having the compiler optimize away the stack smashing
> +	 * we need to do a little something here.
> +	 */
> +	OPTIMIZER_HIDE_VAR(length);
> +
> +	memset(a, 0xa5, length);
> +
> +	printf("We have smashed our stack as this should not exceed 128: sizeof(a) = %zu\n",
> +	       strlen(a));
> +}
> +
> +static noinline void stack_overflow_region(u64 i)
> +{
> +	volatile char a[1024] = {};
> +
> +	if (ctrlc())
> +		return;
> +
> +	RELOC_HIDE(&a, 0);
> +
> +	stack_overflow_region(0);
> +
> +	printf("%*ph", 1024, a);
> +}
> +
> +static int do_stacksmash(int argc, char *argv[])
> +{
> +	if (argc != 2)
> +		return COMMAND_ERROR_USAGE;
> +
> +	if (!strcmp(argv[1], "frame"))
> +		stack_overflow_frame();
> +	else if (!strcmp(argv[1], "region"))
> +		stack_overflow_region(0);
> +
> +	panic("Stack smashing of %s not caught\n", argv[1]);
> +}
> +BAREBOX_CMD_START(stacksmash)
> +        .cmd            = do_stacksmash,
> +        BAREBOX_CMD_DESC("Run stack smashing tests")
> +	BAREBOX_CMD_OPTS("[frame | region]")

Indentation is a bit broken here.

> +        BAREBOX_CMD_GROUP(CMD_GRP_MISC)
> +        BAREBOX_CMD_COMPLETE(empty_complete)
> +BAREBOX_CMD_END
> -- 
> 2.39.2
> 
> 

Best regards
Thorsten