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Message-ID: <202008150952.E81C4A52F@keescook>
Date: Sat, 15 Aug 2020 09:59:56 -0700
From: Kees Cook <keescook@...omium.org>
To: Alexander Popov <alex.popov@...ux.com>
Cc: Jann Horn <jannh@...gle.com>, Will Deacon <will@...nel.org>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
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Joonsoo Kim <iamjoonsoo.kim@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
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Masami Hiramatsu <mhiramat@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Peter Zijlstra <peterz@...radead.org>,
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Subject: Re: [PATCH RFC 2/2] lkdtm: Add heap spraying test
On Thu, Aug 13, 2020 at 06:19:22PM +0300, Alexander Popov wrote:
> Add a simple test for CONFIG_SLAB_QUARANTINE.
>
> It performs heap spraying that aims to reallocate the recently freed heap
> object. This technique is used for exploiting use-after-free
> vulnerabilities in the kernel code.
>
> This test shows that CONFIG_SLAB_QUARANTINE breaks heap spraying
> exploitation technique.
Yay tests!
>
> Signed-off-by: Alexander Popov <alex.popov@...ux.com>
> ---
> drivers/misc/lkdtm/core.c | 1 +
> drivers/misc/lkdtm/heap.c | 40 ++++++++++++++++++++++++++++++++++++++
> drivers/misc/lkdtm/lkdtm.h | 1 +
> 3 files changed, 42 insertions(+)
>
> diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c
> index a5e344df9166..78b7669c35eb 100644
> --- a/drivers/misc/lkdtm/core.c
> +++ b/drivers/misc/lkdtm/core.c
> @@ -126,6 +126,7 @@ static const struct crashtype crashtypes[] = {
> CRASHTYPE(SLAB_FREE_DOUBLE),
> CRASHTYPE(SLAB_FREE_CROSS),
> CRASHTYPE(SLAB_FREE_PAGE),
> + CRASHTYPE(HEAP_SPRAY),
> CRASHTYPE(SOFTLOCKUP),
> CRASHTYPE(HARDLOCKUP),
> CRASHTYPE(SPINLOCKUP),
> diff --git a/drivers/misc/lkdtm/heap.c b/drivers/misc/lkdtm/heap.c
> index 1323bc16f113..a72a241e314a 100644
> --- a/drivers/misc/lkdtm/heap.c
> +++ b/drivers/misc/lkdtm/heap.c
> @@ -205,6 +205,46 @@ static void ctor_a(void *region)
> static void ctor_b(void *region)
> { }
>
> +#define HEAP_SPRAY_SIZE 128
> +
> +void lkdtm_HEAP_SPRAY(void)
> +{
> + int *addr;
> + int *spray_addrs[HEAP_SPRAY_SIZE] = { 0 };
(the 0 isn't needed -- and it was left there, it should be NULL)
> + unsigned long i = 0;
> +
> + addr = kmem_cache_alloc(a_cache, GFP_KERNEL);
I would prefer this test add its own cache (e.g. spray_cache), to avoid
misbehaviors between tests. (e.g. the a and b caches already run the
risk of getting corrupted weirdly.)
> + if (!addr) {
> + pr_info("Unable to allocate memory in lkdtm-heap-a cache\n");
> + return;
> + }
> +
> + *addr = 0x31337;
> + kmem_cache_free(a_cache, addr);
> +
> + pr_info("Performing heap spraying...\n");
> + for (i = 0; i < HEAP_SPRAY_SIZE; i++) {
> + spray_addrs[i] = kmem_cache_alloc(a_cache, GFP_KERNEL);
> + *spray_addrs[i] = 0x31337;
> + pr_info("attempt %lu: spray alloc addr %p vs freed addr %p\n",
> + i, spray_addrs[i], addr);
That's 128 lines spewed into dmesg... I would leave this out.
> + if (spray_addrs[i] == addr) {
> + pr_info("freed addr is reallocated!\n");
> + break;
> + }
> + }
> +
> + if (i < HEAP_SPRAY_SIZE)
> + pr_info("FAIL! Heap spraying succeed :(\n");
I'd move this into the "if (spray_addrs[i] == addr)" test instead of the
pr_info() that is there.
> + else
> + pr_info("OK! Heap spraying hasn't succeed :)\n");
And then make this an "if (i == HEAP_SPRAY_SIZE)" test
> +
> + for (i = 0; i < HEAP_SPRAY_SIZE; i++) {
> + if (spray_addrs[i])
> + kmem_cache_free(a_cache, spray_addrs[i]);
> + }
> +}
> +
> void __init lkdtm_heap_init(void)
> {
> double_free_cache = kmem_cache_create("lkdtm-heap-double_free",
> diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
> index 8878538b2c13..dfafb4ae6f3a 100644
> --- a/drivers/misc/lkdtm/lkdtm.h
> +++ b/drivers/misc/lkdtm/lkdtm.h
> @@ -45,6 +45,7 @@ void lkdtm_READ_BUDDY_AFTER_FREE(void);
> void lkdtm_SLAB_FREE_DOUBLE(void);
> void lkdtm_SLAB_FREE_CROSS(void);
> void lkdtm_SLAB_FREE_PAGE(void);
> +void lkdtm_HEAP_SPRAY(void);
>
> /* lkdtm_perms.c */
> void __init lkdtm_perms_init(void);
> --
> 2.26.2
>
I assume enabling the quarantine defense also ends up being seen in the
SLAB_FREE_DOUBLE LKDTM test too, yes?
--
Kees Cook
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