From: Ingo Molnar <mingo@kernel.org>
To: Darren Hart <dvhart@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] futex: Check for uaddr alignment as early as possible
Date: Tue, 12 Dec 2017 11:23:10 +0100 [thread overview]
Message-ID: <20171212102310.jp6jnw77x6d77rae@gmail.com> (raw)
In-Reply-To: <ed71745a4d33829791c89c37517ba35ab0242b05.1512781589.git.dvhart@infradead.org>
* Darren Hart <dvhart@infradead.org> wrote:
> From: "Darren Hart (VMware)" <dvhart@infradead.org>
>
> uaddr alignment is currently tested by get_futex_key(). We can catch
> misalignment earlier in sys_futex and return -EINVAL sooner. This
> simplifies get_futex_key() a little, but more importantly exits the
> kernel as soon as an invalid parameter is detected.
>
> Passes all selftests/futex testcases on a dual socket Xeon E5-2670, 16
> physical cores total, 32 threads total.
>
> Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Darren Hart <dvhart@infradead.org>
> ---
> kernel/futex.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/futex.c b/kernel/futex.c
> index 76ed592..c3ee6c4 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -509,8 +509,6 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
> * The futex address must be "naturally" aligned.
> */
> key->both.offset = address % PAGE_SIZE;
> - if (unlikely((address % sizeof(u32)) != 0))
> - return -EINVAL;
> address -= key->both.offset;
>
> if (unlikely(!access_ok(rw, uaddr, sizeof(u32))))
> @@ -3525,6 +3523,11 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
> u32 val2 = 0;
> int cmd = op & FUTEX_CMD_MASK;
>
> + /* Only allow for aligned uaddr variables */
> + if (unlikely((unsigned long)uaddr % sizeof(u32) != 0 ||
> + (unsigned long)uaddr2 % sizeof(u32) != 0))
> + return -EINVAL;
> +
> if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI ||
> cmd == FUTEX_WAIT_BITSET ||
> cmd == FUTEX_WAIT_REQUEUE_PI)) {
Yeah, so I applied this yesterday, then -tip started regressing sporadically
during distro networking bring-up, and it took me half a day of debugging to
statistically bisect it back to this patch :-/
So it's apparently broken, but I don't see yet how.
Thanks,
Ingo
prev parent reply other threads:[~2017-12-12 10:23 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-09 1:06 [PATCH] futex: Check for uaddr alignment as early as possible Darren Hart
2017-12-12 10:23 ` Thomas Gleixner
2017-12-12 10:31 ` Ingo Molnar
2017-12-12 15:57 ` Darren Hart
2017-12-12 10:23 ` Ingo Molnar [this message]
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