From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Guenter Roeck <linux@roeck-us.net>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Darren Hart <dvhart@infradead.org>,
linux-arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH] Convert filldir[64]() from __put_user() to unsafe_put_user()
Date: Tue, 15 Oct 2019 20:40:12 +0100 [thread overview]
Message-ID: <20191015194012.GO26530@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CAHk-=wjyiiYhAbzVDUW1F3j9CAcu8+ugSvGYwUivdBfKoeU6yA@mail.gmail.com>
On Tue, Oct 15, 2019 at 12:00:34PM -0700, Linus Torvalds wrote:
> On Tue, Oct 15, 2019 at 11:08 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > Another question: right now we have
> > if (!access_ok(uaddr, sizeof(u32)))
> > return -EFAULT;
> >
> > ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
> > if (ret)
> > return ret;
> > in kernel/futex.c. Would there be any objections to moving access_ok()
> > inside the instances and moving pagefault_disable()/pagefault_enable() outside?
>
> I think we should remove all the "atomic" versions, and just make the
> rule be that if you want atomic, you surround it with
> pagefault_disable()/pagefault_enable().
Umm... I thought about that, but ended up with "it documents the intent" -
pagefault_disable() might be implicit (e.g. done by kmap_atomic()) or
several levels up the call chain. Not sure.
> That covers not just the futex ops (where "atomic" is actually
> somewhat ambiguous - the ops themselves are atomic too, so the naming
> might stay, although arguably the "futex" part makes that pointless
> too), but also copy_to_user_inatomic() and the powerpc version of
> __get_user_inatomic().
Eh? copy_to_user_inatomic() doesn't exist; __copy_to_user_inatomic()
does, but...
arch/mips/kernel/unaligned.c:1307: res = __copy_to_user_inatomic(addr, fpr, sizeof(*fpr));
drivers/gpu/drm/i915/i915_gem.c:313: unwritten = __copy_to_user_inatomic(user_data,
lib/test_kasan.c:510: unused = __copy_to_user_inatomic(usermem, kmem, size + 1);
mm/maccess.c:98: ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
these are all callers it has left anywhere and I'm certainly going to kill it.
Now, __copy_from_user_inatomic() has a lot more callers left... Frankly,
the messier part of API is the nocache side of things. Consider e.g. this:
/* platform specific: cacheless copy */
static void cacheless_memcpy(void *dst, void *src, size_t n)
{
/*
* Use the only available X64 cacheless copy. Add a __user cast
* to quiet sparse. The src agument is already in the kernel so
* there are no security issues. The extra fault recovery machinery
* is not invoked.
*/
__copy_user_nocache(dst, (void __user *)src, n, 0);
}
or this
static void ntb_memcpy_tx(struct ntb_queue_entry *entry, void __iomem *offset)
{
#ifdef ARCH_HAS_NOCACHE_UACCESS
/*
* Using non-temporal mov to improve performance on non-cached
* writes, even though we aren't actually copying from user space.
*/
__copy_from_user_inatomic_nocache(offset, entry->buf, entry->len);
#else
memcpy_toio(offset, entry->buf, entry->len);
#endif
/* Ensure that the data is fully copied out before setting the flags */
wmb();
ntb_tx_copy_callback(entry, NULL);
}
"user" part is bollocks in both cases; moreover, I really wonder about that
ifdef in ntb one - ARCH_HAS_NOCACHE_UACCESS is x86-only *at* *the* *moment*
and it just so happens that ..._toio() doesn't require anything special on
x86. Have e.g. arm grow nocache stuff and the things will suddenly break,
won't they?
next prev parent reply other threads:[~2019-10-15 19:40 UTC|newest]
Thread overview: 75+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-06 22:20 [PATCH] Convert filldir[64]() from __put_user() to unsafe_put_user() Guenter Roeck
2019-10-06 23:06 ` Linus Torvalds
2019-10-06 23:35 ` Linus Torvalds
2019-10-07 0:04 ` Guenter Roeck
2019-10-07 1:17 ` Linus Torvalds
2019-10-07 1:24 ` Al Viro
2019-10-07 2:06 ` Linus Torvalds
2019-10-07 2:50 ` Al Viro
2019-10-07 3:11 ` Linus Torvalds
2019-10-07 15:40 ` David Laight
2019-10-07 18:11 ` Linus Torvalds
2019-10-08 9:58 ` David Laight
2019-10-07 17:34 ` Al Viro
2019-10-07 18:13 ` Linus Torvalds
2019-10-07 18:22 ` Al Viro
2019-10-07 18:26 ` Linus Torvalds
2019-10-07 18:36 ` Tony Luck
2019-10-07 19:08 ` Linus Torvalds
2019-10-07 19:49 ` Tony Luck
2019-10-07 20:04 ` Linus Torvalds
2019-10-08 3:29 ` Al Viro
2019-10-08 4:09 ` Linus Torvalds
2019-10-08 4:14 ` Linus Torvalds
2019-10-08 5:02 ` Al Viro
2019-10-08 4:24 ` Linus Torvalds
2019-10-10 19:55 ` Al Viro
2019-10-10 22:12 ` Linus Torvalds
2019-10-11 0:11 ` Al Viro
2019-10-11 0:31 ` Linus Torvalds
2019-10-13 18:13 ` Al Viro
2019-10-13 18:43 ` Linus Torvalds
2019-10-13 19:10 ` Al Viro
2019-10-13 19:22 ` Linus Torvalds
2019-10-13 19:59 ` Al Viro
2019-10-13 20:20 ` Linus Torvalds
2019-10-15 3:46 ` Michael Ellerman
2019-10-15 18:08 ` Al Viro
2019-10-15 19:00 ` Linus Torvalds
2019-10-15 19:40 ` Al Viro [this message]
2019-10-15 20:18 ` Al Viro
2019-10-16 12:12 ` [RFC] change of calling conventions for arch_futex_atomic_op_inuser() Al Viro
2019-10-16 12:24 ` Thomas Gleixner
2019-10-16 20:25 ` [PATCH] Convert filldir[64]() from __put_user() to unsafe_put_user() Al Viro
2019-10-17 19:36 ` [RFC][PATCHES] drivers/scsi/sg.c uaccess cleanups/fixes Al Viro
2019-10-17 19:39 ` [RFC PATCH 1/8] sg_ioctl(): fix copyout handling Al Viro
2019-10-17 19:39 ` [RFC PATCH 2/8] sg_new_write(): replace access_ok() + __copy_from_user() with copy_from_user() Al Viro
2019-10-17 19:39 ` [RFC PATCH 3/8] sg_write(): __get_user() can fail Al Viro
2019-10-17 19:39 ` [RFC PATCH 4/8] sg_read(): simplify reading ->pack_id of userland sg_io_hdr_t Al Viro
2019-10-17 19:39 ` [RFC PATCH 5/8] sg_new_write(): don't bother with access_ok Al Viro
2019-10-17 19:39 ` [RFC PATCH 6/8] sg_read(): get rid of access_ok()/__copy_..._user() Al Viro
2019-10-17 19:39 ` [RFC PATCH 7/8] sg_write(): get rid of access_ok()/__copy_from_user()/__get_user() Al Viro
2019-10-17 19:39 ` [RFC PATCH 8/8] SG_IO: get rid of access_ok() Al Viro
2019-10-17 21:44 ` [RFC][PATCHES] drivers/scsi/sg.c uaccess cleanups/fixes Douglas Gilbert
2019-11-05 4:54 ` Martin K. Petersen
2019-11-05 5:25 ` Al Viro
2019-11-06 4:29 ` Martin K. Petersen
2019-10-18 0:27 ` [RFC] csum_and_copy_from_user() semantics Al Viro
2019-10-25 14:01 ` [PATCH] Convert filldir[64]() from __put_user() to unsafe_put_user() Thomas Gleixner
2019-10-08 4:57 ` Al Viro
2019-10-08 13:14 ` Greg KH
2019-10-08 15:29 ` Al Viro
2019-10-08 15:38 ` Greg KH
2019-10-08 17:06 ` Al Viro
2019-10-08 19:58 ` Al Viro
2019-10-08 20:16 ` Al Viro
2019-10-08 20:34 ` Al Viro
2019-10-07 2:30 ` Guenter Roeck
2019-10-07 3:12 ` Linus Torvalds
2019-10-07 0:23 ` Guenter Roeck
2019-10-07 4:04 ` Max Filippov
2019-10-07 12:16 ` Guenter Roeck
2019-10-07 19:21 ` Linus Torvalds
2019-10-07 20:29 ` Guenter Roeck
2019-10-07 23:27 ` Guenter Roeck
2019-10-08 6:28 ` Geert Uytterhoeven
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