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Date:   Thu, 9 Sep 2021 08:49:57 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] lkdtm: Use init_uts_ns.name instead of macros

On Wed, Sep 01, 2021 at 04:34:06PM -0700, Kees Cook wrote:
> Using generated/compile.h triggered a full LKDTM rebuild with every
> build. Avoid this by using the exported strings instead.
> 
> Fixes: b8661450bc7f ("lkdtm: Add kernel version to failure hints")
> Signed-off-by: Kees Cook <keescook@...omium.org>

Hi Greg,

Your bot said "please wait, the merge window is open", but it'd be really
nice to get this into -rc1 to avoid annoying people doing rebuilds...

:)

-Kees

> ---
>  drivers/misc/lkdtm/core.c  | 10 ++++++++++
>  drivers/misc/lkdtm/lkdtm.h | 28 +++++++++++++++++-----------
>  2 files changed, 27 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
> index 95b1c6800a22..fe6fd34b8caf 100644
> --- a/drivers/misc/lkdtm/core.c
> +++ b/drivers/misc/lkdtm/core.c
> @@ -26,6 +26,7 @@
>  #include <linux/init.h>
>  #include <linux/slab.h>
>  #include <linux/debugfs.h>
> +#include <linux/utsname.h>
>  
>  #define DEFAULT_COUNT 10
>  
> @@ -210,6 +211,8 @@ module_param(cpoint_count, int, 0644);
>  MODULE_PARM_DESC(cpoint_count, " Crash Point Count, number of times the "\
>  				"crash point is to be hit to trigger action");
>  
> +/* For test debug reporting. */
> +char *lkdtm_kernel_info;
>  
>  /* Return the crashtype number or NULL if the name is invalid */
>  static const struct crashtype *find_crashtype(const char *name)
> @@ -490,6 +493,11 @@ static int __init lkdtm_module_init(void)
>  	crash_count = cpoint_count;
>  #endif
>  
> +	/* Common initialization. */
> +	lkdtm_kernel_info = kasprintf(GFP_KERNEL, "kernel (%s %s)",
> +				      init_uts_ns.name.release,
> +				      init_uts_ns.name.machine);
> +
>  	/* Handle test-specific initialization. */
>  	lkdtm_bugs_init(&recur_count);
>  	lkdtm_perms_init();
> @@ -538,6 +546,8 @@ static void __exit lkdtm_module_exit(void)
>  	if (lkdtm_kprobe != NULL)
>  		unregister_kprobe(lkdtm_kprobe);
>  
> +	kfree(lkdtm_kernel_info);
> +
>  	pr_info("Crash point unregistered\n");
>  }
>  
> diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
> index d7d64d9765eb..c212a253edde 100644
> --- a/drivers/misc/lkdtm/lkdtm.h
> +++ b/drivers/misc/lkdtm/lkdtm.h
> @@ -5,17 +5,17 @@
>  #define pr_fmt(fmt) "lkdtm: " fmt
>  
>  #include <linux/kernel.h>
> -#include <generated/compile.h>
> -#include <generated/utsrelease.h>
>  
> -#define LKDTM_KERNEL "kernel (" UTS_RELEASE " " UTS_MACHINE ")"
> +extern char *lkdtm_kernel_info;
>  
>  #define pr_expected_config(kconfig)				\
>  {								\
>  	if (IS_ENABLED(kconfig)) 				\
> -		pr_err("Unexpected! This " LKDTM_KERNEL " was built with " #kconfig "=y\n"); \
> +		pr_err("Unexpected! This %s was built with " #kconfig "=y\n", \
> +			lkdtm_kernel_info);			\
>  	else							\
> -		pr_warn("This is probably expected, since this " LKDTM_KERNEL " was built *without* " #kconfig "=y\n"); \
> +		pr_warn("This is probably expected, since this %s was built *without* " #kconfig "=y\n", \
> +			lkdtm_kernel_info);			\
>  }
>  
>  #ifndef MODULE
> @@ -25,24 +25,30 @@ int lkdtm_check_bool_cmdline(const char *param);
>  	if (IS_ENABLED(kconfig)) {				\
>  		switch (lkdtm_check_bool_cmdline(param)) {	\
>  		case 0:						\
> -			pr_warn("This is probably expected, since this " LKDTM_KERNEL " was built with " #kconfig "=y but booted with '" param "=N'\n"); \
> +			pr_warn("This is probably expected, since this %s was built with " #kconfig "=y but booted with '" param "=N'\n", \
> +				lkdtm_kernel_info);		\
>  			break;					\
>  		case 1:						\
> -			pr_err("Unexpected! This " LKDTM_KERNEL " was built with " #kconfig "=y and booted with '" param "=Y'\n"); \
> +			pr_err("Unexpected! This %s was built with " #kconfig "=y and booted with '" param "=Y'\n", \
> +				lkdtm_kernel_info);		\
>  			break;					\
>  		default:					\
> -			pr_err("Unexpected! This " LKDTM_KERNEL " was built with " #kconfig "=y (and booted without '" param "' specified)\n"); \
> +			pr_err("Unexpected! This %s was built with " #kconfig "=y (and booted without '" param "' specified)\n", \
> +				lkdtm_kernel_info);		\
>  		}						\
>  	} else {						\
>  		switch (lkdtm_check_bool_cmdline(param)) {	\
>  		case 0:						\
> -			pr_warn("This is probably expected, as this " LKDTM_KERNEL " was built *without* " #kconfig "=y and booted with '" param "=N'\n"); \
> +			pr_warn("This is probably expected, as this %s was built *without* " #kconfig "=y and booted with '" param "=N'\n", \
> +				lkdtm_kernel_info);		\
>  			break;					\
>  		case 1:						\
> -			pr_err("Unexpected! This " LKDTM_KERNEL " was built *without* " #kconfig "=y but booted with '" param "=Y'\n"); \
> +			pr_err("Unexpected! This %s was built *without* " #kconfig "=y but booted with '" param "=Y'\n", \
> +				lkdtm_kernel_info);		\
>  			break;					\
>  		default:					\
> -			pr_err("This is probably expected, since this " LKDTM_KERNEL " was built *without* " #kconfig "=y (and booted without '" param "' specified)\n"); \
> +			pr_err("This is probably expected, since this %s was built *without* " #kconfig "=y (and booted without '" param "' specified)\n", \
> +				lkdtm_kernel_info);		\
>  			break;					\
>  		}						\
>  	}							\
> -- 
> 2.30.2
> 

-- 
Kees Cook

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