linux-kernel - Re: [PATCH 1/2] mmap locking API: Order lock of nascent mm outside lock of live mm

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Message-ID: <CAG48ez0LuG9nULaBF_3ofE--u=TBgbxVdACthpb8wtJhADO02w@mail.gmail.com>
Date:   Mon, 5 Oct 2020 03:30:43 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Michel Lespinasse <walken@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        linux-um@...ts.infradead.org, Jason Gunthorpe <jgg@...dia.com>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH 1/2] mmap locking API: Order lock of nascent mm outside
 lock of live mm

On Sat, Oct 3, 2020 at 11:30 PM Michel Lespinasse <walken@...gle.com> wrote:
> Unrelated to the above: copy_from_user and copy_to_user should not be
> called with mmap_lock held; it may be worth adding these assertions
> too (probably in separate patches) ?

We already have that: All (hopefully?) the userspace accessors call
might_fault(), and that does might_lock_read(&current->mm->mmap_lock)
(if we're not running in a lazytlb kernel thread or KERNEL_DS is on or
we're in IRQ context or page faults have explicitly been disabled).


But another place where lockdep asserts should be added is find_vma();
there are currently several architectures that sometimes improperly
call that with no lock held:

SPARC's arch_validate_prot():
https://lore.kernel.org/linux-mm/CAG48ez3YsfTfOFKa-Po58e4PNp7FK54MFbkK3aUPSRt3LWtxQA@mail.gmail.com/

nios2 sys_cacheflush():
https://lore.kernel.org/linux-mm/CAG48ez3hxeXU29UGWRH-gRXX2jb5Lc==npbXFt8UDrWO4eHZdQ@mail.gmail.com/

nds32 sys_cacheflush():
https://lore.kernel.org/linux-mm/CAG48ez1UnQEMok9rqFQC4XHBaMmBe=eaedu8Z_RXdjFHTna_LA@mail.gmail.com/