[PATCH v3 1/3] Fix userfaultfd_api to return EINVAL as expected

[PATCH v3 1/3] Fix userfaultfd_api to return EINVAL as expected

[Audra Mitchell]

Currently if we request a feature that is not set in the Kernel
config we fail silently and return all the available features. However,
the man page indicates we should return an EINVAL.

We need to fix this issue since we can end up with a Kernel warning
should a program request the feature UFFD_FEATURE_WP_UNPOPULATED on
a kernel with the config not set with this feature.

 [  200.812896] WARNING: CPU: 91 PID: 13634 at mm/memory.c:1660 zap_pte_range+0x43d/0x660
 [  200.820738] Modules linked in:
 [  200.869387] CPU: 91 PID: 13634 Comm: userfaultfd Kdump: loaded Not tainted 6.9.0-rc5+ #8
 [  200.877477] Hardware name: Dell Inc. PowerEdge R6525/0N7YGH, BIOS 2.7.3 03/30/2022
 [  200.885052] RIP: 0010:zap_pte_range+0x43d/0x660

Fixes: e06f1e1dd499 ("userfaultfd: wp: enabled write protection in userfaultfd API")
Signed-off-by: Audra Mitchell <audra@redhat.com>
---
 fs/userfaultfd.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index eee7320ab0b0..17e409ceaa33 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -2057,7 +2057,7 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
 		goto out;
 	features = uffdio_api.features;
 	ret = -EINVAL;
-	if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES))
+	if (uffdio_api.api != UFFD_API)
 		goto err_out;
 	ret = -EPERM;
 	if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
@@ -2081,6 +2081,11 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
 	uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
 	uffdio_api.features &= ~UFFD_FEATURE_WP_ASYNC;
 #endif
+
+	ret = -EINVAL;
+	if (features & ~uffdio_api.features)
+		goto err_out;
+
 	uffdio_api.ioctls = UFFD_API_IOCTLS;
 	ret = -EFAULT;
 	if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
-- 
2.44.0

[PATCH v3 2/3] Update uffd-stress to handle EINVAL for unset config features

[Audra Mitchell]

Now that we have updated userfaultfd_api to correctly return
EIVAL when a feature is requested but not available, let's fix
the uffd-stress test to only set the UFFD_FEATURE_WP_UNPOPULATED
feature when the config is set. In addition, still run the test if
the CONFIG_PTE_MARKER_UFFD_WP is not set, just dont use the corresponding
UFFD_FEATURE_WP_UNPOPULATED feature.

Signed-off-by: Audra Mitchell <audra@redhat.com>
---
 tools/testing/selftests/mm/uffd-stress.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/mm/uffd-stress.c b/tools/testing/selftests/mm/uffd-stress.c
index f78bab0f3d45..b9b6d858eab8 100644
--- a/tools/testing/selftests/mm/uffd-stress.c
+++ b/tools/testing/selftests/mm/uffd-stress.c
@@ -38,6 +38,8 @@
 
 #ifdef __NR_userfaultfd
 
+uint64_t features;
+
 #define BOUNCE_RANDOM		(1<<0)
 #define BOUNCE_RACINGFAULTS	(1<<1)
 #define BOUNCE_VERIFY		(1<<2)
@@ -247,10 +249,14 @@ static int userfaultfd_stress(void)
 	unsigned long nr;
 	struct uffd_args args[nr_cpus];
 	uint64_t mem_size = nr_pages * page_size;
+	int flags = 0;
 
 	memset(args, 0, sizeof(struct uffd_args) * nr_cpus);
 
-	if (uffd_test_ctx_init(UFFD_FEATURE_WP_UNPOPULATED, NULL))
+	if (features & UFFD_FEATURE_WP_UNPOPULATED && test_type == TEST_ANON)
+		flags = UFFD_FEATURE_WP_UNPOPULATED;
+
+	if (uffd_test_ctx_init(flags, NULL))
 		err("context init failed");
 
 	if (posix_memalign(&area, page_size, page_size))
@@ -385,8 +391,6 @@ static void set_test_type(const char *type)
 
 static void parse_test_type_arg(const char *raw_type)
 {
-	uint64_t features = UFFD_API_FEATURES;
-
 	set_test_type(raw_type);
 
 	if (!test_type)
@@ -409,8 +413,8 @@ static void parse_test_type_arg(const char *raw_type)
 	 * feature.
 	 */
 
-	if (userfaultfd_open(&features))
-		err("Userfaultfd open failed");
+	if (uffd_get_features(&features))
+		err("failed to get available features");
 
 	test_uffdio_wp = test_uffdio_wp &&
 		(features & UFFD_FEATURE_PAGEFAULT_FLAG_WP);
-- 
2.44.0

[PATCH v3 3/3] Turn off test_uffdio_wp if CONFIG_PTE_MARKER_UFFD_WP is not configured.

[Audra Mitchell]

If CONFIG_PTE_MARKER_UFFD_WP is disabled, then we turn off three features
in userfaultfd_api (UFFD_FEATURE_WP_HUGETLBFS_SHMEM,
UFFD_FEATURE_WP_UNPOPULATED, and UFFD_FEATURE_WP_ASYNC). Currently this
test always will call uffdio_regsiter with the flag
UFFDIO_REGISTER_MODE_WP. However, the kernel ensures in vma_can_userfault
that if the feature UFFD_FEATURE_WP_HUGETLBFS_SHMEM is disabled, only
allow the VM_UFFD_WP on anonymous vmas, meaning our call to
uffdio_regsiter will fail. We still want to be able to run the test even
if we have CONFIG_PTE_MARKER_UFFD_WP disabled, so check to see if the
feature UFFD_FEATURE_WP_HUGETLBFS_SHMEM has been turned off in the test
and if so, disable us from calling uffdio_regsiter with the flag
UFFDIO_REGISTER_MODE_WP.

Signed-off-by: Audra Mitchell <audra@redhat.com>
---
 tools/testing/selftests/mm/uffd-stress.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/testing/selftests/mm/uffd-stress.c b/tools/testing/selftests/mm/uffd-stress.c
index b9b6d858eab8..3266ae885f75 100644
--- a/tools/testing/selftests/mm/uffd-stress.c
+++ b/tools/testing/selftests/mm/uffd-stress.c
@@ -419,6 +419,9 @@ static void parse_test_type_arg(const char *raw_type)
 	test_uffdio_wp = test_uffdio_wp &&
 		(features & UFFD_FEATURE_PAGEFAULT_FLAG_WP);
 
+	if (test_type != TEST_ANON && !(features & UFFD_FEATURE_WP_HUGETLBFS_SHMEM))
+		test_uffdio_wp = false;
+
 	close(uffd);
 	uffd = -1;
 }
-- 
2.44.0

Re: [PATCH v3 3/3] Turn off test_uffdio_wp if CONFIG_PTE_MARKER_UFFD_WP is not configured.

[Peter Xu]

On Wed, Jun 26, 2024 at 09:05:13AM -0400, Audra Mitchell wrote:
> If CONFIG_PTE_MARKER_UFFD_WP is disabled, then we turn off three features
> in userfaultfd_api (UFFD_FEATURE_WP_HUGETLBFS_SHMEM,
> UFFD_FEATURE_WP_UNPOPULATED, and UFFD_FEATURE_WP_ASYNC). Currently this
> test always will call uffdio_regsiter with the flag
> UFFDIO_REGISTER_MODE_WP. However, the kernel ensures in vma_can_userfault
> that if the feature UFFD_FEATURE_WP_HUGETLBFS_SHMEM is disabled, only
> allow the VM_UFFD_WP on anonymous vmas, meaning our call to
> uffdio_regsiter will fail. We still want to be able to run the test even
> if we have CONFIG_PTE_MARKER_UFFD_WP disabled, so check to see if the
> feature UFFD_FEATURE_WP_HUGETLBFS_SHMEM has been turned off in the test
> and if so, disable us from calling uffdio_regsiter with the flag
> UFFDIO_REGISTER_MODE_WP.
> 
> Signed-off-by: Audra Mitchell <audra@redhat.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

> ---
>  tools/testing/selftests/mm/uffd-stress.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/tools/testing/selftests/mm/uffd-stress.c b/tools/testing/selftests/mm/uffd-stress.c
> index b9b6d858eab8..3266ae885f75 100644
> --- a/tools/testing/selftests/mm/uffd-stress.c
> +++ b/tools/testing/selftests/mm/uffd-stress.c
> @@ -419,6 +419,9 @@ static void parse_test_type_arg(const char *raw_type)
>  	test_uffdio_wp = test_uffdio_wp &&
>  		(features & UFFD_FEATURE_PAGEFAULT_FLAG_WP);
>  
> +	if (test_type != TEST_ANON && !(features & UFFD_FEATURE_WP_HUGETLBFS_SHMEM))
> +		test_uffdio_wp = false;
> +
>  	close(uffd);
>  	uffd = -1;
>  }
> -- 
> 2.44.0
> 

-- 
Peter Xu