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-rw-r--r--Documentation/vm/userfaultfd.txt12
-rw-r--r--fs/userfaultfd.c79
-rw-r--r--include/uapi/linux/userfaultfd.h70
3 files changed, 108 insertions, 53 deletions
diff --git a/Documentation/vm/userfaultfd.txt b/Documentation/vm/userfaultfd.txt
index 90912925425e..70a3c94d1941 100644
--- a/Documentation/vm/userfaultfd.txt
+++ b/Documentation/vm/userfaultfd.txt
@@ -46,11 +46,13 @@ is a corner case that would currently return -EBUSY).
When first opened the userfaultfd must be enabled invoking the
UFFDIO_API ioctl specifying a uffdio_api.api value set to UFFD_API (or
a later API version) which will specify the read/POLLIN protocol
-userland intends to speak on the UFFD. The UFFDIO_API ioctl if
-successful (i.e. if the requested uffdio_api.api is spoken also by the
-running kernel), will return into uffdio_api.features and
-uffdio_api.ioctls two 64bit bitmasks of respectively the activated
-feature of the read(2) protocol and the generic ioctl available.
+userland intends to speak on the UFFD and the uffdio_api.features
+userland requires. The UFFDIO_API ioctl if successful (i.e. if the
+requested uffdio_api.api is spoken also by the running kernel and the
+requested features are going to be enabled) will return into
+uffdio_api.features and uffdio_api.ioctls two 64bit bitmasks of
+respectively all the available features of the read(2) protocol and
+the generic ioctl available.
Once the userfaultfd has been enabled the UFFDIO_REGISTER ioctl should
be invoked (if present in the returned uffdio_api.ioctls bitmask) to
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 0756d97b0666..1f2ddaaf3c03 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -50,7 +50,7 @@ struct userfaultfd_ctx {
};
struct userfaultfd_wait_queue {
- unsigned long address;
+ struct uffd_msg msg;
wait_queue_t wq;
bool pending;
struct userfaultfd_ctx *ctx;
@@ -77,7 +77,8 @@ static int userfaultfd_wake_function(wait_queue_t *wq, unsigned mode,
/* len == 0 means wake all */
start = range->start;
len = range->len;
- if (len && (start > uwq->address || start + len <= uwq->address))
+ if (len && (start > uwq->msg.arg.pagefault.address ||
+ start + len <= uwq->msg.arg.pagefault.address))
goto out;
ret = wake_up_state(wq->private, mode);
if (ret)
@@ -135,28 +136,43 @@ static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
}
}
-static inline unsigned long userfault_address(unsigned long address,
- unsigned int flags,
- unsigned long reason)
+static inline void msg_init(struct uffd_msg *msg)
{
- BUILD_BUG_ON(PAGE_SHIFT < UFFD_BITS);
- address &= PAGE_MASK;
+ BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
+ /*
+ * Must use memset to zero out the paddings or kernel data is
+ * leaked to userland.
+ */
+ memset(msg, 0, sizeof(struct uffd_msg));
+}
+
+static inline struct uffd_msg userfault_msg(unsigned long address,
+ unsigned int flags,
+ unsigned long reason)
+{
+ struct uffd_msg msg;
+ msg_init(&msg);
+ msg.event = UFFD_EVENT_PAGEFAULT;
+ msg.arg.pagefault.address = address;
if (flags & FAULT_FLAG_WRITE)
/*
- * Encode "write" fault information in the LSB of the
- * address read by userland, without depending on
- * FAULT_FLAG_WRITE kernel internal value.
+ * If UFFD_FEATURE_PAGEFAULT_FLAG_WRITE was set in the
+ * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE
+ * was not set in a UFFD_EVENT_PAGEFAULT, it means it
+ * was a read fault, otherwise if set it means it's
+ * a write fault.
*/
- address |= UFFD_BIT_WRITE;
+ msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
if (reason & VM_UFFD_WP)
/*
- * Encode "reason" fault information as bit number 1
- * in the address read by userland. If bit number 1 is
- * clear it means the reason is a VM_FAULT_MISSING
- * fault.
+ * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
+ * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was
+ * not set in a UFFD_EVENT_PAGEFAULT, it means it was
+ * a missing fault, otherwise if set it means it's a
+ * write protect fault.
*/
- address |= UFFD_BIT_WP;
- return address;
+ msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
+ return msg;
}
/*
@@ -242,7 +258,7 @@ int handle_userfault(struct vm_area_struct *vma, unsigned long address,
init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
uwq.wq.private = current;
- uwq.address = userfault_address(address, flags, reason);
+ uwq.msg = userfault_msg(address, flags, reason);
uwq.pending = true;
uwq.ctx = ctx;
@@ -398,7 +414,7 @@ static unsigned int userfaultfd_poll(struct file *file, poll_table *wait)
}
static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
- __u64 *addr)
+ struct uffd_msg *msg)
{
ssize_t ret;
DECLARE_WAITQUEUE(wait, current);
@@ -416,8 +432,8 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
* disappear from under us.
*/
uwq->pending = false;
- /* careful to always initialize addr if ret == 0 */
- *addr = uwq->address;
+ /* careful to always initialize msg if ret == 0 */
+ *msg = uwq->msg;
spin_unlock(&ctx->fault_wqh.lock);
ret = 0;
break;
@@ -447,8 +463,7 @@ static ssize_t userfaultfd_read(struct file *file, char __user *buf,
{
struct userfaultfd_ctx *ctx = file->private_data;
ssize_t _ret, ret = 0;
- /* careful to always initialize addr if ret == 0 */
- __u64 uninitialized_var(addr);
+ struct uffd_msg msg;
int no_wait = file->f_flags & O_NONBLOCK;
if (ctx->state == UFFD_STATE_WAIT_API)
@@ -456,16 +471,16 @@ static ssize_t userfaultfd_read(struct file *file, char __user *buf,
BUG_ON(ctx->state != UFFD_STATE_RUNNING);
for (;;) {
- if (count < sizeof(addr))
+ if (count < sizeof(msg))
return ret ? ret : -EINVAL;
- _ret = userfaultfd_ctx_read(ctx, no_wait, &addr);
+ _ret = userfaultfd_ctx_read(ctx, no_wait, &msg);
if (_ret < 0)
return ret ? ret : _ret;
- if (put_user(addr, (__u64 __user *) buf))
+ if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
return ret ? ret : -EFAULT;
- ret += sizeof(addr);
- buf += sizeof(addr);
- count -= sizeof(addr);
+ ret += sizeof(msg);
+ buf += sizeof(msg);
+ count -= sizeof(msg);
/*
* Allow to read more than one fault at time but only
* block if waiting for the very first one.
@@ -873,17 +888,15 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
if (ctx->state != UFFD_STATE_WAIT_API)
goto out;
ret = -EFAULT;
- if (copy_from_user(&uffdio_api, buf, sizeof(__u64)))
+ if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
goto out;
- if (uffdio_api.api != UFFD_API) {
- /* careful not to leak info, we only read the first 8 bytes */
+ if (uffdio_api.api != UFFD_API || uffdio_api.features) {
memset(&uffdio_api, 0, sizeof(uffdio_api));
if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
goto out;
ret = -EINVAL;
goto out;
}
- /* careful not to leak info, we only read the first 8 bytes */
uffdio_api.features = UFFD_API_FEATURES;
uffdio_api.ioctls = UFFD_API_IOCTLS;
ret = -EFAULT;
diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index 330206016249..a5f8825381ef 100644
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -11,9 +11,15 @@
#include <linux/types.h>
+#include <linux/compiler.h>
+
#define UFFD_API ((__u64)0xAA)
-/* FIXME: add "|UFFD_FEATURE_WP" to UFFD_API_FEATURES after implementing it */
-#define UFFD_API_FEATURES (UFFD_FEATURE_WRITE_BIT)
+/*
+ * After implementing the respective features it will become:
+ * #define UFFD_API_FEATURES (UFFD_FEATURE_PAGEFAULT_FLAG_WP | \
+ * UFFD_FEATURE_EVENT_FORK)
+ */
+#define UFFD_API_FEATURES (0)
#define UFFD_API_IOCTLS \
((__u64)1 << _UFFDIO_REGISTER | \
(__u64)1 << _UFFDIO_UNREGISTER | \
@@ -45,26 +51,60 @@
#define UFFDIO_WAKE _IOR(UFFDIO, _UFFDIO_WAKE, \
struct uffdio_range)
-/*
- * Valid bits below PAGE_SHIFT in the userfault address read through
- * the read() syscall.
- */
-#define UFFD_BIT_WRITE (1<<0) /* this was a write fault, MISSING or WP */
-#define UFFD_BIT_WP (1<<1) /* handle_userfault() reason VM_UFFD_WP */
-#define UFFD_BITS 2 /* two above bits used for UFFD_BIT_* mask */
+/* read() structure */
+struct uffd_msg {
+ __u8 event;
+
+ __u8 reserved1;
+ __u16 reserved2;
+ __u32 reserved3;
+
+ union {
+ struct {
+ __u64 flags;
+ __u64 address;
+ } pagefault;
+
+ struct {
+ /* unused reserved fields */
+ __u64 reserved1;
+ __u64 reserved2;
+ __u64 reserved3;
+ } reserved;
+ } arg;
+} __packed;
/*
- * Features reported in uffdio_api.features field
+ * Start at 0x12 and not at 0 to be more strict against bugs.
*/
-#define UFFD_FEATURE_WRITE_BIT (1<<0) /* Corresponds to UFFD_BIT_WRITE */
-#define UFFD_FEATURE_WP_BIT (1<<1) /* Corresponds to UFFD_BIT_WP */
+#define UFFD_EVENT_PAGEFAULT 0x12
+#if 0 /* not available yet */
+#define UFFD_EVENT_FORK 0x13
+#endif
+
+/* flags for UFFD_EVENT_PAGEFAULT */
+#define UFFD_PAGEFAULT_FLAG_WRITE (1<<0) /* If this was a write fault */
+#define UFFD_PAGEFAULT_FLAG_WP (1<<1) /* If reason is VM_UFFD_WP */
struct uffdio_api {
- /* userland asks for an API number */
+ /* userland asks for an API number and the features to enable */
__u64 api;
-
- /* kernel answers below with the available features for the API */
+ /*
+ * Kernel answers below with the all available features for
+ * the API, this notifies userland of which events and/or
+ * which flags for each event are enabled in the current
+ * kernel.
+ *
+ * Note: UFFD_EVENT_PAGEFAULT and UFFD_PAGEFAULT_FLAG_WRITE
+ * are to be considered implicitly always enabled in all kernels as
+ * long as the uffdio_api.api requested matches UFFD_API.
+ */
+#if 0 /* not available yet */
+#define UFFD_FEATURE_PAGEFAULT_FLAG_WP (1<<0)
+#define UFFD_FEATURE_EVENT_FORK (1<<1)
+#endif
__u64 features;
+
__u64 ioctls;
};
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-18 08:21:50 +0100