linux-hardening - Re: [PATCH v2 3/4] selftests/mm: mseal

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Message-ID: <q3xvzsnyltr2gdgnecgw74umi2yrjvimkxo7bvgnqb4darakzw@jahjkavgcyfm>
Date: Fri, 30 Aug 2024 13:57:06 +0100
From: Pedro Falcato <pedro.falcato@...il.com>
To: jeffxu@...omium.org
Cc: akpm@...ux-foundation.org, linux-kselftest@...r.kernel.org, 
	linux-mm@...ck.org, linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org, 
	willy@...radead.org, lorenzo.stoakes@...cle.com, broonie@...nel.org, vbabka@...e.cz, 
	Liam.Howlett@...cle.com, rientjes@...gle.com, keescook@...omium.org
Subject: Re: [PATCH v2 3/4] selftests/mm: mseal_test add more tests for mmap

On Thu, Aug 29, 2024 at 09:43:51PM GMT, jeffxu@...omium.org wrote:
> From: Jeff Xu <jeffxu@...omium.org>
> 
> Add sealing test to cover mmap for
> Expand/shrink across vmas.
> Reuse the same address in !MAP_FIXED case.
> 
> Signed-off-by: Jeff Xu <jeffxu@...omium.org>
> ---
>  tools/testing/selftests/mm/mseal_test.c | 125 +++++++++++++++++++++++-
>  1 file changed, 124 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/mm/mseal_test.c b/tools/testing/selftests/mm/mseal_test.c
> index ae06c354220d..d83538039e76 100644
> --- a/tools/testing/selftests/mm/mseal_test.c
> +++ b/tools/testing/selftests/mm/mseal_test.c
> @@ -2222,6 +2222,122 @@ static void test_munmap_free_multiple_ranges(bool seal)
>  	REPORT_TEST_PASS();
>  }
>  
> +static void test_seal_mmap_expand_seal_middle(bool seal)
> +{
> +	void *ptr;
> +	unsigned long page_size = getpagesize();
> +	unsigned long size = 12 * page_size;
> +	int ret;
> +	void *ret2;
> +	int prot;
> +
> +	setup_single_address(size, &ptr);
> +	FAIL_TEST_IF_FALSE(ptr != (void *)-1);
> +	/* ummap last 4 pages. */
> +	ret = sys_munmap(ptr + 8 * page_size, 4 * page_size);
> +	FAIL_TEST_IF_FALSE(!ret);
> +
> +	size = get_vma_size(ptr, &prot);
> +	FAIL_TEST_IF_FALSE(size == 8 * page_size);
> +	FAIL_TEST_IF_FALSE(prot == 0x4);
> +
> +	if (seal) {
> +		ret = sys_mseal(ptr + 4 * page_size, 4 * page_size);
> +		FAIL_TEST_IF_FALSE(!ret);
> +	}
> +
> +	/* use mmap to expand. */
> +	ret2 = mmap(ptr, 12 * page_size, PROT_READ,
> +			MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0);

This is not expansion, but overwriting. Expansion is allowed through an adjacent mmap + mseal (which will merge the two VMAs).

> +	if (seal) {
> +		FAIL_TEST_IF_FALSE(ret2 == MAP_FAILED);
> +		FAIL_TEST_IF_FALSE(errno == EPERM);
> +
> +		size = get_vma_size(ptr, &prot);
> +		FAIL_TEST_IF_FALSE(size == 4 * page_size);
> +		FAIL_TEST_IF_FALSE(prot == 0x4);
> +
> +		size = get_vma_size(ptr + 4 * page_size, &prot);
> +		FAIL_TEST_IF_FALSE(size == 4 * page_size);
> +		FAIL_TEST_IF_FALSE(prot == 0x4);
> +	} else
> +		FAIL_TEST_IF_FALSE(ret2 == ptr);
> +
> +	REPORT_TEST_PASS();
> +}
> +
> +static void test_seal_mmap_shrink_seal_middle(bool seal)
> +{
> +	void *ptr;
> +	unsigned long page_size = getpagesize();
> +	unsigned long size = 12 * page_size;
> +	int ret;
> +	void *ret2;
> +	int prot;
> +
> +	setup_single_address(size, &ptr);
> +	FAIL_TEST_IF_FALSE(ptr != (void *)-1);
> +
> +	if (seal) {
> +		ret = sys_mseal(ptr + 4 * page_size, 4 * page_size);
> +		FAIL_TEST_IF_FALSE(!ret);
> +	}
> +
> +	/* use mmap to shrink. */
> +	ret2 = mmap(ptr, 7 * page_size, PROT_READ,
> +			MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED, -1, 0);

This is also a partial overwrite.

> +	if (seal) {
> +		FAIL_TEST_IF_FALSE(ret2 == MAP_FAILED);
> +		FAIL_TEST_IF_FALSE(errno == EPERM);
> +
> +		size = get_vma_size(ptr, &prot);
> +		FAIL_TEST_IF_FALSE(size == 4 * page_size);
> +		FAIL_TEST_IF_FALSE(prot == 0x4);
> +
> +		size = get_vma_size(ptr + 4 * page_size, &prot);
> +		FAIL_TEST_IF_FALSE(size == 4 * page_size);
> +		FAIL_TEST_IF_FALSE(prot == 0x4);
> +
> +		size = get_vma_size(ptr + 4 * page_size, &prot);
> +		FAIL_TEST_IF_FALSE(size == 4 * page_size);
> +		FAIL_TEST_IF_FALSE(prot == 0x4);
> +	} else
> +		FAIL_TEST_IF_FALSE(ret2 == ptr);
> +
> +	REPORT_TEST_PASS();
> +}
> +
> +static void test_seal_mmap_reuse_addr(bool seal)
> +{
> +	void *ptr;
> +	unsigned long page_size = getpagesize();
> +	unsigned long size = page_size;
> +	int ret;
> +	void *ret2;
> +	int prot;
> +
> +	setup_single_address(size, &ptr);
> +	FAIL_TEST_IF_FALSE(ptr != (void *)-1);
> +
> +	if (seal) {
> +		ret = sys_mseal(ptr, size);
> +		FAIL_TEST_IF_FALSE(!ret);
> +	}
> +
> +	/* use mmap to change protection. */
> +	ret2 = mmap(ptr, size, PROT_NONE,
> +			MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> +

This is also an overwrite. You're semantically testing the same thing, and testing the same regions of code.
These 3 tests are all kind of the same thing.

-- 
Pedro