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Message-ID: <CAGXu5jLREPiCHSwk1LGKJm0pPGpD8O4S+4xu5=Aw_x+COLBXWg@mail.gmail.com>
Date: Fri, 19 Feb 2016 11:12:42 -0800
From: Kees Cook <keescook@...omium.org>
To: Laura Abbott <labbott@...oraproject.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Arnd Bergmann <arnd@...db.de>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2] lkdtm: Add READ_AFTER_FREE test
On Thu, Feb 18, 2016 at 5:15 PM, Laura Abbott <labbott@...oraproject.org> wrote:
>
> In a similar manner to WRITE_AFTER_FREE, add a READ_AFTER_FREE
> test to test free poisoning features. Sample output when
> no sanitization is present:
>
> [ 22.414170] lkdtm: Performing direct entry READ_AFTER_FREE
> [ 22.415124] lkdtm: Value in memory before free: 12345678
> [ 22.415900] lkdtm: Attempting to read from freed memory
> [ 22.416394] lkdtm: Successfully read value: 12345678
>
> with sanitization:
>
> [ 25.874585] lkdtm: Performing direct entry READ_AFTER_FREE
> [ 25.875527] lkdtm: Value in memory before free: 12345678
> [ 25.876382] lkdtm: Attempting to read from freed memory
> [ 25.876900] general protection fault: 0000 [#1] SMP
>
> Signed-off-by: Laura Abbott <labbott@...oraproject.org>
Excellent! Could you mention in the changelog which CONFIG (or runtime
values) will change the lkdtm test? (I thought there was a poisoning
style that would result in a zero-read instead of a GP?)
-Kees
> ---
> I split this out from the previous series
> (http://article.gmane.org/gmane.linux.kernel.mm/143486) since
> that series is going to be going in more incrementally.
> Having the test in sooner than later will be helpful I think
>
> v2: Tweaked the output text to be clearer about what's going on.
> Switched to using the middle of an allocated block instead of the beginning.
> ---
> drivers/misc/lkdtm.c | 34 ++++++++++++++++++++++++++++++++++
> 1 file changed, 34 insertions(+)
>
> diff --git a/drivers/misc/lkdtm.c b/drivers/misc/lkdtm.c
> index 11fdadc..24d0ac7 100644
> --- a/drivers/misc/lkdtm.c
> +++ b/drivers/misc/lkdtm.c
> @@ -92,6 +92,7 @@ enum ctype {
> CT_UNALIGNED_LOAD_STORE_WRITE,
> CT_OVERWRITE_ALLOCATION,
> CT_WRITE_AFTER_FREE,
> + CT_READ_AFTER_FREE,
> CT_SOFTLOCKUP,
> CT_HARDLOCKUP,
> CT_SPINLOCKUP,
> @@ -129,6 +130,7 @@ static char* cp_type[] = {
> "UNALIGNED_LOAD_STORE_WRITE",
> "OVERWRITE_ALLOCATION",
> "WRITE_AFTER_FREE",
> + "READ_AFTER_FREE",
> "SOFTLOCKUP",
> "HARDLOCKUP",
> "SPINLOCKUP",
> @@ -417,6 +419,38 @@ static void lkdtm_do_action(enum ctype which)
> memset(data, 0x78, len);
> break;
> }
> + case CT_READ_AFTER_FREE: {
> + int **base;
> + int *val, *tmp;
> + size_t len = 1024;
> + /*
> + * The slub allocator uses the first word to store the free
> + * pointer in some configurations. Use the middle of the
> + * allocation to avoid running into the freelist
> + */
> + size_t offset = (len/sizeof(int *))/2;
> +
> + base = kmalloc(len, GFP_KERNEL);
> + if (!base)
> + return;
> +
> + val = kmalloc(len, GFP_KERNEL);
> + if (!val)
> + return;
> +
> + *val = 0x12345678;
> + pr_info("Value in memory before free: %x\n", *val);
> +
> + base[offset] = val;
> + kfree(base);
> +
> + tmp = base[offset];
> + pr_info("Attempting to read from freed memory");
> + pr_info("Successfully read value: %x\n", *tmp);
> +
> + kfree(val);
> + break;
> + }
> case CT_SOFTLOCKUP:
> preempt_disable();
> for (;;)
> --
> 2.5.0
>
--
Kees Cook
Chrome OS & Brillo Security
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