linux-kernel - Re: [PATCH v4 0/7] arm64: untag user pointers passed to the kernel

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Date:   Tue, 31 Jul 2018 15:23:21 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Robin Murphy <robin.murphy@....com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Shuah Khan <shuah@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-doc@...r.kernel.org,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-arch@...r.kernel.org, linux-kselftest@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Lee Smith <Lee.Smith@....com>,
        Kostya Serebryany <kcc@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Evgeniy Stepanov <eugenis@...gle.com>
Subject: Re: [PATCH v4 0/7] arm64: untag user pointers passed to the kernel

On Mon, Jul 16, 2018 at 1:25 PM, Andrey Konovalov <andreyknvl@...gle.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?

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