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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Tue, 31 Jul 2018 15:23:21 +0200
Message-ID: <CAAeHK+y95YJZ6yEw0icsz7ScFYP=x5V+__8J0BG9T3vyB1J1xA@mail.gmail.com>
Subject: Re: [PATCH v4 0/7] arm64: untag user pointers passed to the kernel
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     Will Deacon <will.deacon@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Kees Cook <keescook@chromium.org>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Shuah Khan <shuah@kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        linux-doc@vger.kernel.org,
        Linux Memory Management List <linux-mm@kvack.org>,
        linux-arch@vger.kernel.org, linux-kselftest@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        Chintan Pandya <cpandya@codeaurora.org>,
        Jacob Bramley <Jacob.Bramley@arm.com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>,
        Lee Smith <Lee.Smith@arm.com>,
        Kostya Serebryany <kcc@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>,
        Evgeniy Stepanov <eugenis@google.com>
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On Mon, Jul 16, 2018 at 1:25 PM, Andrey Konovalov <andreyknvl@google.com> wrote:
> So the checker reports ~100 different places where a __user pointer
> being casted. I've looked through them and found 3 places where we
> need to add untagging. Source code lines below come from 4.18-rc2+
> (6f0d349d).
>
> Place 1:
>
> arch/arm64/mm/fault.c:302:34: warning: user pointer cast
> current->thread.fault_address = (unsigned long)info->si_addr;
>
> Compare a pointer with TASK_SIZE (1 << 48) to check whether it lies in
> the kernel or in user space. Need to untag the address before
> performing a comparison.
>
> Place 2:
>
> fs/namespace.c:2736:21: warning: user pointer cast
> size = TASK_SIZE - (unsigned long)data;
>
> A similar check performed by subtracting a pointer from TASK_SIZE.
> Need to untag before subtracting.
>
> Place 3:
>
> drivers/usb/core/devio.c:1407:29: warning: user pointer cast
> unsigned long uurb_start = (unsigned long)uurb->buffer;
> drivers/usb/core/devio.c:1636:31: warning: user pointer cast
> unsigned long uurb_start = (unsigned long)uurb->buffer;
> drivers/usb/core/devio.c:1715:30: warning: user pointer cast
> unsigned long uurb_start = (unsigned long)uurb->buffer;
>
> The device keeps list of mmapped areas and searches them for provided
> __user pointer. Need to untag before searching.
>
> There are also a few cases of memory syscalls operating on __user
> pointers instead of unsigned longs like mmap:
>
> ipc/shm.c:1355:23: warning: user pointer cast
> unsigned long addr = (unsigned long)shmaddr;
> ipc/shm.c:1566:23: warning: user pointer cast
> unsigned long addr = (unsigned long)shmaddr;
> mm/migrate.c:1586:10: warning: user pointer cast
> addr = (unsigned long)p;
> mm/migrate.c:1660:24: warning: user pointer cast
> unsigned long addr = (unsigned long)(*pages);
>
> If we don't add untagging to mmap, we probably don't need it here.
>
> The rest of reported places look fine as is. Full annotated results of
> running the checker are here [2].
>
> I'll add the 3 patches with fixes to v5 of this patchset.
>
> Catalin, WDYT?

ping