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Date: Fri, 5 Aug 2022 15:11:46 +0200
From: David Hildenbrand <david@...hat.com>
To: Chao Peng <chao.p.peng@...ux.intel.com>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
linux-doc@...r.kernel.org, qemu-devel@...gnu.org,
linux-kselftest@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Jonathan Corbet <corbet@....net>,
Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
Hugh Dickins <hughd@...gle.com>,
Jeff Layton <jlayton@...nel.org>,
"J . Bruce Fields" <bfields@...ldses.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Shuah Khan <shuah@...nel.org>, Mike Rapoport <rppt@...nel.org>,
Steven Price <steven.price@....com>,
"Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
Vlastimil Babka <vbabka@...e.cz>,
Vishal Annapurve <vannapurve@...gle.com>,
Yu Zhang <yu.c.zhang@...ux.intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
ak@...ux.intel.com, aarcange@...hat.com, ddutile@...hat.com,
dhildenb@...hat.com, Quentin Perret <qperret@...gle.com>,
Michael Roth <michael.roth@....com>, mhocko@...e.com,
Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v7 02/14] selftests/memfd: Add tests for
F_SEAL_AUTO_ALLOCATE
On 06.07.22 10:20, Chao Peng wrote:
> Add tests to verify sealing memfds with the F_SEAL_AUTO_ALLOCATE works
> as expected.
>
> Signed-off-by: Chao Peng <chao.p.peng@...ux.intel.com>
> ---
> tools/testing/selftests/memfd/memfd_test.c | 166 +++++++++++++++++++++
> 1 file changed, 166 insertions(+)
>
> diff --git a/tools/testing/selftests/memfd/memfd_test.c b/tools/testing/selftests/memfd/memfd_test.c
> index 94df2692e6e4..b849ece295fd 100644
> --- a/tools/testing/selftests/memfd/memfd_test.c
> +++ b/tools/testing/selftests/memfd/memfd_test.c
> @@ -9,6 +9,7 @@
> #include <fcntl.h>
> #include <linux/memfd.h>
> #include <sched.h>
> +#include <setjmp.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <signal.h>
> @@ -232,6 +233,31 @@ static void mfd_fail_open(int fd, int flags, mode_t mode)
> }
> }
>
> +static void mfd_assert_fallocate(int fd)
> +{
> + int r;
> +
> + r = fallocate(fd, 0, 0, mfd_def_size);
> + if (r < 0) {
> + printf("fallocate(ALLOC) failed: %m\n");
> + abort();
> + }
> +}
> +
> +static void mfd_assert_punch_hole(int fd)
> +{
> + int r;
> +
> + r = fallocate(fd,
> + FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> + 0,
> + mfd_def_size);
> + if (r < 0) {
> + printf("fallocate(PUNCH_HOLE) failed: %m\n");
> + abort();
> + }
> +}
> +
> static void mfd_assert_read(int fd)
> {
> char buf[16];
> @@ -594,6 +620,94 @@ static void mfd_fail_grow_write(int fd)
> }
> }
>
> +static void mfd_assert_hole_write(int fd)
> +{
> + ssize_t l;
> + void *p;
> + char *p1;
> +
> + /*
> + * huegtlbfs does not support write, but we want to
> + * verify everything else here.
> + */
> + if (!hugetlbfs_test) {
> + /* verify direct write() succeeds */
> + l = write(fd, "\0\0\0\0", 4);
> + if (l != 4) {
> + printf("write() failed: %m\n");
> + abort();
> + }
> + }
> +
> + /* verify mmaped write succeeds */
> + p = mmap(NULL,
> + mfd_def_size,
> + PROT_READ | PROT_WRITE,
> + MAP_SHARED,
> + fd,
> + 0);
> + if (p == MAP_FAILED) {
> + printf("mmap() failed: %m\n");
> + abort();
> + }
> + p1 = (char *)p + mfd_def_size - 1;
> + *p1 = 'H';
> + if (*p1 != 'H') {
> + printf("mmaped write failed: %m\n");
> + abort();
> +
> + }
> + munmap(p, mfd_def_size);
> +}
> +
> +sigjmp_buf jbuf, *sigbuf;
> +static void sig_handler(int sig, siginfo_t *siginfo, void *ptr)
> +{
> + if (sig == SIGBUS) {
> + if (sigbuf)
> + siglongjmp(*sigbuf, 1);
> + abort();
> + }
> +}
> +
> +static void mfd_fail_hole_write(int fd)
> +{
> + ssize_t l;
> + void *p;
> + char *p1;
> +
> + /* verify direct write() fails */
> + l = write(fd, "data", 4);
> + if (l > 0) {
> + printf("expected failure on write(), but got %d: %m\n", (int)l);
> + abort();
> + }
> +
> + /* verify mmaped write fails */
> + p = mmap(NULL,
> + mfd_def_size,
> + PROT_READ | PROT_WRITE,
> + MAP_SHARED,
> + fd,
> + 0);
> + if (p == MAP_FAILED) {
> + printf("mmap() failed: %m\n");
> + abort();
> + }
> +
> + sigbuf = &jbuf;
> + if (sigsetjmp(*sigbuf, 1))
> + goto out;
> +
> + /* Below write should trigger SIGBUS signal */
> + p1 = (char *)p + mfd_def_size - 1;
> + *p1 = 'H';
Maybe you want to verify separately, that bothj
> + printf("failed to receive SIGBUS for mmaped write: %m\n");
> + abort();
> +out:
> + munmap(p, mfd_def_size);
> +}
> +
> static int idle_thread_fn(void *arg)
> {
> sigset_t set;
> @@ -880,6 +994,57 @@ static void test_seal_resize(void)
> close(fd);
> }
>
> +/*
> + * Test F_SEAL_AUTO_ALLOCATE
> + * Test whether F_SEAL_AUTO_ALLOCATE actually prevents allocation.
> + */
> +static void test_seal_auto_allocate(void)
> +{
> + struct sigaction act;
> + int fd;
> +
> + printf("%s SEAL-AUTO-ALLOCATE\n", memfd_str);
> +
> + memset(&act, 0, sizeof(act));
> + act.sa_sigaction = sig_handler;
> + act.sa_flags = SA_SIGINFO;
> + if (sigaction(SIGBUS, &act, 0)) {
> + printf("sigaction() failed: %m\n");
> + abort();
> + }
> +
> + fd = mfd_assert_new("kern_memfd_seal_auto_allocate",
> + mfd_def_size,
> + MFD_CLOEXEC | MFD_ALLOW_SEALING);
> +
> + /* read/write should pass if F_SEAL_AUTO_ALLOCATE not set */
> + mfd_assert_read(fd);
> + mfd_assert_hole_write(fd);
> +
> + mfd_assert_has_seals(fd, 0);
> + mfd_assert_add_seals(fd, F_SEAL_AUTO_ALLOCATE);
> + mfd_assert_has_seals(fd, F_SEAL_AUTO_ALLOCATE);
> +
> + /* read/write should pass for pre-allocated area */
> + mfd_assert_read(fd);
> + mfd_assert_hole_write(fd);
> +
> + mfd_assert_punch_hole(fd);
> +
> + /* read should pass, write should fail in hole */
> + mfd_assert_read(fd);
> + mfd_fail_hole_write(fd);
> +
> + mfd_assert_fallocate(fd);
> +
> + /* read/write should pass after fallocate */
> + mfd_assert_read(fd);
> + mfd_assert_hole_write(fd);
> +
> + close(fd);
> +}
What might make sense is to verify for the following operations:
* read()
* write()
* read via mmap
* write via mmap
After sealing on a hole, that there is *still* a hole and that only the
read() might succeed, with a comment stating that shmem optimized for
read on holes by reading from the shared zeropage.
I'd suggest decoupling hole_write from hole_mmap_write and similarly
have hole_read and hole_mmap_read.
You should be able to use fstat() to obtain the number of allocated
blocks to check that fairly easily.
--
Thanks,
David / dhildenb
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