linux-kernel - Re: [PATCH 6/7] lkdtm: crash on overwriting protected pmalloc var

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Message-ID: <1723ee8d-c89e-0704-c2c3-254eda39dc8b@gmail.com>
Date:   Tue, 6 Mar 2018 09:20:04 -0800
From:   J Freyensee <why2jjj.linux@...il.com>
To:     Igor Stoppa <igor.stoppa@...wei.com>, david@...morbit.com,
        willy@...radead.org, keescook@...omium.org, mhocko@...nel.org
Cc:     labbott@...hat.com, linux-security-module@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 6/7] lkdtm: crash on overwriting protected pmalloc var



On 2/28/18 12:06 PM, Igor Stoppa wrote:
> Verify that pmalloc read-only protection is in place: trying to
> overwrite a protected variable will crash the kernel.
>
> Signed-off-by: Igor Stoppa <igor.stoppa@...wei.com>
> ---
>   drivers/misc/lkdtm.h       |  1 +
>   drivers/misc/lkdtm_core.c  |  3 +++
>   drivers/misc/lkdtm_perms.c | 28 ++++++++++++++++++++++++++++
>   3 files changed, 32 insertions(+)
>
> diff --git a/drivers/misc/lkdtm.h b/drivers/misc/lkdtm.h
> index 9e513dcfd809..dcda3ae76ceb 100644
> --- a/drivers/misc/lkdtm.h
> +++ b/drivers/misc/lkdtm.h
> @@ -38,6 +38,7 @@ void lkdtm_READ_BUDDY_AFTER_FREE(void);
>   void __init lkdtm_perms_init(void);
>   void lkdtm_WRITE_RO(void);
>   void lkdtm_WRITE_RO_AFTER_INIT(void);
> +void lkdtm_WRITE_RO_PMALLOC(void);

Does this need some sort of #ifdef too?

>   void lkdtm_WRITE_KERN(void);
>   void lkdtm_EXEC_DATA(void);
>   void lkdtm_EXEC_STACK(void);
> diff --git a/drivers/misc/lkdtm_core.c b/drivers/misc/lkdtm_core.c
> index 2154d1bfd18b..c9fd42bda6ee 100644
> --- a/drivers/misc/lkdtm_core.c
> +++ b/drivers/misc/lkdtm_core.c
> @@ -155,6 +155,9 @@ static const struct crashtype crashtypes[] = {
>   	CRASHTYPE(ACCESS_USERSPACE),
>   	CRASHTYPE(WRITE_RO),
>   	CRASHTYPE(WRITE_RO_AFTER_INIT),
> +#ifdef CONFIG_PROTECTABLE_MEMORY
> +	CRASHTYPE(WRITE_RO_PMALLOC),
> +#endif
>   	CRASHTYPE(WRITE_KERN),
>   	CRASHTYPE(REFCOUNT_INC_OVERFLOW),
>   	CRASHTYPE(REFCOUNT_ADD_OVERFLOW),
> diff --git a/drivers/misc/lkdtm_perms.c b/drivers/misc/lkdtm_perms.c
> index 53b85c9d16b8..0ac9023fd2b0 100644
> --- a/drivers/misc/lkdtm_perms.c
> +++ b/drivers/misc/lkdtm_perms.c
> @@ -9,6 +9,7 @@
>   #include <linux/vmalloc.h>
>   #include <linux/mman.h>
>   #include <linux/uaccess.h>
> +#include <linux/pmalloc.h>
>   #include <asm/cacheflush.h>
>   
>   /* Whether or not to fill the target memory area with do_nothing(). */
> @@ -104,6 +105,33 @@ void lkdtm_WRITE_RO_AFTER_INIT(void)
>   	*ptr ^= 0xabcd1234;
>   }
>   
> +#ifdef CONFIG_PROTECTABLE_MEMORY
> +void lkdtm_WRITE_RO_PMALLOC(void)
> +{
> +	struct gen_pool *pool;
> +	int *i;
> +
> +	pool = pmalloc_create_pool("pool", 0);
> +	if (unlikely(!pool)) {
> +		pr_info("Failed preparing pool for pmalloc test.");
> +		return;
> +	}
> +
> +	i = (int *)pmalloc(pool, sizeof(int), GFP_KERNEL);
> +	if (unlikely(!i)) {
> +		pr_info("Failed allocating memory for pmalloc test.");
> +		pmalloc_destroy_pool(pool);
> +		return;
> +	}
> +
> +	*i = INT_MAX;
> +	pmalloc_protect_pool(pool);
> +
> +	pr_info("attempting bad pmalloc write at %p\n", i);
> +	*i = 0;

OK, now I'm on the right version of this patch series, same comment 
applies.  I don't get the local *i assignment at the end of the 
function, but seems harmless.

Except the two minor comments, otherwise,
Reviewed-by: Jay Freyensee <why2jjj.linux@...il.com>

> +}
> +#endif
> +
>   void lkdtm_WRITE_KERN(void)
>   {
>   	size_t size;