futex: Flag conversion

Futex has 3 sets of flags:

 - legacy futex op bits
 - futex2 flags
 - internal flags

Add a few helpers to convert from the API flags into the internal
flags.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: André Almeida <andrealmeid@igalia.com>
Link: https://lore.kernel.org/r/20230921105247.722140574@noisy.programming.kicks-ass.net

Author: peterz@infradead.org

kernel/futex/futex.h

@@ -5,6 +5,7 @@
 #include <linux/futex.h>
 #include <linux/rtmutex.h>
 #include <linux/sched/wake_q.h>
+#include <linux/compat.h>
 
 #ifdef CONFIG_PREEMPT_RT
 #include <linux/rcuwait.h>
@@ -16,17 +17,73 @@
  * Futex flags used to encode options to functions and preserve them across
  * restarts.
  */
+#define FLAGS_SIZE_8		0x00
+#define FLAGS_SIZE_16		0x01
+#define FLAGS_SIZE_32		0x02
+#define FLAGS_SIZE_64		0x03
+
+#define FLAGS_SIZE_MASK		0x03
+
 #ifdef CONFIG_MMU
-# define FLAGS_SHARED		0x01
+# define FLAGS_SHARED		0x10
 #else
 /*
  * NOMMU does not have per process address space. Let the compiler optimize
  * code away.
  */
 # define FLAGS_SHARED		0x00
 #endif
-#define FLAGS_CLOCKRT		0x02
-#define FLAGS_HAS_TIMEOUT	0x04
+#define FLAGS_CLOCKRT		0x20
+#define FLAGS_HAS_TIMEOUT	0x40
+#define FLAGS_NUMA		0x80
+
+/* FUTEX_ to FLAGS_ */
+static inline unsigned int futex_to_flags(unsigned int op)
+{
+	unsigned int flags = FLAGS_SIZE_32;
+
+	if (!(op & FUTEX_PRIVATE_FLAG))
+		flags |= FLAGS_SHARED;
+
+	if (op & FUTEX_CLOCK_REALTIME)
+		flags |= FLAGS_CLOCKRT;
+
+	return flags;
+}
+
+/* FUTEX2_ to FLAGS_ */
+static inline unsigned int futex2_to_flags(unsigned int flags2)
+{
+	unsigned int flags = flags2 & FUTEX2_SIZE_MASK;
+
+	if (!(flags2 & FUTEX2_PRIVATE))
+		flags |= FLAGS_SHARED;
+
+	if (flags2 & FUTEX2_NUMA)
+		flags |= FLAGS_NUMA;
+
+	return flags;
+}
+
+static inline unsigned int futex_size(unsigned int flags)
+{
+	return 1 << (flags & FLAGS_SIZE_MASK);
+}
+
+static inline bool futex_flags_valid(unsigned int flags)
+{
+	/* Only 64bit futexes for 64bit code */
+	if (!IS_ENABLED(CONFIG_64BIT) || in_compat_syscall()) {
+		if ((flags & FLAGS_SIZE_MASK) == FLAGS_SIZE_64)
+			return false;
+	}
+
+	/* Only 32bit futexes are implemented -- for now */
+	if ((flags & FLAGS_SIZE_MASK) != FLAGS_SIZE_32)
+		return false;
+
+	return true;
+}
 
 #ifdef CONFIG_FAIL_FUTEX
 extern bool should_fail_futex(bool fshared);

kernel/futex/syscalls.c

@@ -1,6 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
-#include <linux/compat.h>
 #include <linux/syscalls.h>
 #include <linux/time_namespace.h>
 
@@ -85,15 +84,12 @@ SYSCALL_DEFINE3(get_robust_list, int, pid,
 long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
 		u32 __user *uaddr2, u32 val2, u32 val3)
 {
+	unsigned int flags = futex_to_flags(op);
 	int cmd = op & FUTEX_CMD_MASK;
-	unsigned int flags = 0;
 
-	if (!(op & FUTEX_PRIVATE_FLAG))
-		flags |= FLAGS_SHARED;
-
-	if (op & FUTEX_CLOCK_REALTIME) {
-		flags |= FLAGS_CLOCKRT;
-		if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
+	if (flags & FLAGS_CLOCKRT) {
+		if (cmd != FUTEX_WAIT_BITSET &&
+		    cmd != FUTEX_WAIT_REQUEUE_PI &&
 		    cmd != FUTEX_LOCK_PI2)
 			return -ENOSYS;
 	}
@@ -201,21 +197,19 @@ static int futex_parse_waitv(struct futex_vector *futexv,
 	unsigned int i;
 
 	for (i = 0; i < nr_futexes; i++) {
+		unsigned int flags;
+
 		if (copy_from_user(&aux, &uwaitv[i], sizeof(aux)))
 			return -EFAULT;
 
 		if ((aux.flags & ~FUTEX2_VALID_MASK) || aux.__reserved)
 			return -EINVAL;
 
-		if (!IS_ENABLED(CONFIG_64BIT) || in_compat_syscall()) {
-			if ((aux.flags & FUTEX2_SIZE_MASK) == FUTEX2_SIZE_U64)
-				return -EINVAL;
-		}
-
-		if ((aux.flags & FUTEX2_SIZE_MASK) != FUTEX2_SIZE_U32)
+		flags = futex2_to_flags(aux.flags);
+		if (!futex_flags_valid(flags))
 			return -EINVAL;
 
-		futexv[i].w.flags = aux.flags;
+		futexv[i].w.flags = flags;
 		futexv[i].w.val = aux.val;
 		futexv[i].w.uaddr = aux.uaddr;
 		futexv[i].q = futex_q_init;

kernel/futex/waitwake.c

@@ -419,11 +419,11 @@ static int futex_wait_multiple_setup(struct futex_vector *vs, int count, int *wo
 	 */
 retry:
 	for (i = 0; i < count; i++) {
-		if ((vs[i].w.flags & FUTEX_PRIVATE_FLAG) && retry)
+		if (!(vs[i].w.flags & FLAGS_SHARED) && retry)
 			continue;
 
 		ret = get_futex_key(u64_to_user_ptr(vs[i].w.uaddr),
-				    !(vs[i].w.flags & FUTEX_PRIVATE_FLAG),
+				    vs[i].w.flags & FLAGS_SHARED,
 				    &vs[i].q.key, FUTEX_READ);
 
 		if (unlikely(ret))