Jens Axboe <axboe@xxxxxxxxx> writes:
> From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxx>
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> ---
> kernel/futex/futex.h | 64 +++++++++++++++++++++++++++++++++++++++--
> kernel/futex/syscalls.c | 24 ++++++----------
> kernel/futex/waitwake.c | 4 +--
> 3 files changed, 72 insertions(+), 20 deletions(-)
>
> diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
> index b5379c0e6d6d..c0e04599904a 100644
> --- a/kernel/futex/futex.h
> +++ b/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>
> @@ -16,8 +17,15 @@
> * 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 +33,58 @@
> */
> # 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;
FUTEX2_64 -> FLAGS_SIZE_MASK
> +
> + if (!(flags2 & FUTEX2_PRIVATE))
> + flags |= FLAGS_SHARED;
> +
> + if (flags2 & FUTEX2_NUMA)
> + flags |= FLAGS_NUMA;
> +
> + return flags;
> +}
> +
> +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;
> + }
I read the comment above as '64bit code can only have 64bit futexes',
which is obviously wrong and not what the code is checking.
Something like this would be better:
/* Reject 64bit futexes on !64bit code. */
Or Perhaps make it generic:
/* Don't allow futexes larger than the word size */
if (futex_size(flags) > (__WORDSIZE/8) || in_compat_syscall())
--
Gabriel Krisman Bertazi
