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Date:   Sun, 1 Nov 2020 22:27:38 +0100
From:   =?utf-8?B?UGF3ZcWC?= Jasiak <pawel@jasiak.xyz>
To:     linux-kernel@vger.kernel.org
Cc:     linux-fsdevel@vger.kernel.org, jack@suse.cz
Subject: PROBLEM: fanotify_mark EFAULT on x86
Message-ID: <20201101212738.GA16924@gmail.com>
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I am trying to run examples from man fanotify.7 but fanotify_mark always
fail with errno =3D EFAULT.

fanotify_mark declaration is

SYSCALL_DEFINE5(fanotify_mark, int, fanotify_fd, unsigned int, flags,
			      __u64, mask, int, dfd,
			      const char  __user *, pathname)

When=20

fanotify_mark(4, FAN_MARK_ADD | FAN_MARK_ONLYDIR,
              FAN_CREATE | FAN_ONDIR, AT_FDCWD, 0xdeadc0de)

is called on kernel side I can see in do_syscall_32_irqs_on that CPU
context is
    bx =3D 0x4        =3D 4
    cx =3D 0x9        =3D FAN_MARK_ADD | FAN_MARK_ONLYDIR,
    dx =3D 0x40000100 =3D FAN_CREATE | FAN_ONDIR
    si =3D 0x0
    di =3D 0xffffff9c =3D AT_FDCWD
    bp =3D 0xdeadc0de
    ax =3D 0xffffffda
    orix_ax =3D 0x153

I am not sure if it is ok because third argument is uint64_t so if I
understand correctly mask should be divided into two registers (dx and
si).

But in fanotify_mark we get
    fanotify_fd =3D 4          =3D bx
    flags       =3D 0x9        =3D cx
    mask        =3D 0x40000100 =3D dx
    dfd         =3D 0          =3D si
    pathname    =3D 0xffffff9c =3D di

I believe that correct order is
    fanotify_fd =3D 4          =3D bx
    flags       =3D 0x9        =3D cx
    mask        =3D 0x40000100 =3D (si << 32) | dx
    dfd         =3D 0xffffff9c =3D di
    pathname    =3D 0xdeadc0de =3D bp

I think that we should call COMPAT version of fanotify_mark here

COMPAT_SYSCALL_DEFINE6(fanotify_mark,
				int, fanotify_fd, unsigned int, flags,
				__u32, mask0, __u32, mask1, int, dfd,
				const char  __user *, pathname)

or something wrong is with 64-bits arguments.

I am running Linux 5.9.2 i686 on Pentium III (Coppermine).
For tests I am using Debian sid on qemu with 5.9.2 and default kernel
=66rom repositories.

Everything works fine on 5.5 and 5.4.

--=20

Pawe=C5=82 Jasiak

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