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Message-ID: <CABi2SkUtCqLj49rpm4+vB1+SqaT9YAuAVwVj6PpaDbkJStZSVg@mail.gmail.com>
Date: Fri, 30 Aug 2024 08:52:56 -0700
From: Jeff Xu <jeffxu@...omium.org>
To: Pedro Falcato <pedro.falcato@...il.com>
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
Hi Pedro
On Fri, Aug 30, 2024 at 5:57 AM Pedro Falcato <pedro.falcato@...il.com> wrote:
>
> 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).
The mmap is trying to expand the address range beginning from ptr
(size 8 * page_size) to 12 * page_size. This is overwrite + expansion.
>
> > + 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.
The mmap is trying to shrink the address range beginning from ptr
(size 12 * page_size) to 8 * page_size. This is overwrite + shrink.
>
> > + 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.
This is not overwriting. MAP_FIXED is not used.
-Jeff
> These 3 tests are all kind of the same thing.
>
> --
> Pedro
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