[PATCH 03/10] futex: Flag conversion

Jens Axboe
2023-07-20T22:19:14Z

From: Peter Zijlstra <peterz@infradead.org>

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>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
kernel/futex/futex.h | 48 ++++++++++++++++++++++++++++++++++++++---
kernel/futex/syscalls.c | 21 +++++++++++-------
kernel/futex/waitwake.c | 4 ++--
3 files changed, 60 insertions(+), 13 deletions(-)

diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
index b5379c0e6d6d..54f4470b7db8 100644
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -16,8 +16,15 @@
* 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
@@ -25,8 +32,43 @@
*/
# 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_64;
+
+ 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)
+{
+ unsigned int size = flags & FLAGS_SIZE_MASK;
+ return 1 << size; /* {0,1,2,3} -> {1,2,4,8} */
+}

#ifdef CONFIG_FAIL_FUTEX
extern bool should_fail_futex(bool fshared);
diff --git a/kernel/futex/syscalls.c b/kernel/futex/syscalls.c
index d5bb6dad22fe..7234538a490d 100644
--- a/kernel/futex/syscalls.c
+++ b/kernel/futex/syscalls.c
@@ -85,15 +85,12 @@ 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;
}
@@ -201,6 +198,8 @@ static int futex_parse_waitv(struct futex_vector *futexv,
unsigned int i;

for (i = 0; i < nr_futexes; i++) {
+ unsigned int bits, flags;
+
if (copy_from_user(&aux, &uwaitv[i], sizeof(aux)))
return -EFAULT;

@@ -210,7 +209,13 @@ static int futex_parse_waitv(struct futex_vector *futexv,
if ((aux.flags & FUTEX2_64) != FUTEX2_32)
return -EINVAL;

- futexv[i].w.flags = aux.flags;
+ flags = futex2_to_flags(aux.flags);
+ bits = 8 * futex_size(flags);
+
+ if (bits < 64 && aux.val >> bits)
+ return -EINVAL;
+
+ futexv[i].w.flags = flags;
futexv[i].w.val = aux.val;
futexv[i].w.uaddr = aux.uaddr;
futexv[i].q = futex_q_init;
diff --git a/kernel/futex/waitwake.c b/kernel/futex/waitwake.c
index ba01b9408203..fa9757766103 100644
--- a/kernel/futex/waitwake.c
+++ b/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))
--
2.40.1