linux-kernel - Re: [PATCH v3 05/46] x86: asm: instrument usercopy in get_user() and __put_user

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Date:   Wed, 27 Apr 2022 09:14:48 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Alexander Potapenko <glider@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Christoph Hellwig <hch@....de>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 05/46] x86: asm: instrument usercopy in get_user() and __put_user_size()

On Tue, Apr 26, 2022 at 6:42 PM Alexander Potapenko <glider@...gle.com> wrote:
> @@ -99,11 +100,13 @@ extern int __get_user_bad(void);
>         int __ret_gu;                                                   \
>         register __inttype(*(ptr)) __val_gu asm("%"_ASM_DX);            \
>         __chk_user_ptr(ptr);                                            \
> +       instrument_copy_from_user_before((void *)&(x), ptr, sizeof(*(ptr))); \
>         asm volatile("call __" #fn "_%P4"                               \
>                      : "=a" (__ret_gu), "=r" (__val_gu),                \
>                         ASM_CALL_CONSTRAINT                             \
>                      : "0" (ptr), "i" (sizeof(*(ptr))));                \
>         (x) = (__force __typeof__(*(ptr))) __val_gu;                    \
> +       instrument_copy_from_user_after((void *)&(x), ptr, sizeof(*(ptr)), 0); \

Isn't "ptr" the original pointer here? I think what happened with the
reported warning is that you get one output line for every instance this
is used in. There should probably be a

      __auto_type __ptr = (ptr);

at the beginning of the macro to ensure that 'ptr' is only evaluated once.

>>> arch/x86/kernel/signal.c:360:9: sparse: sparse: incorrect type in argument 1 (different address spaces) @@     expected void [noderef] __user *to @@     got unsigned long long [usertype] * @@

It would also make sense to add the missing __user annotation in this line, but
I suspect there are others like it in drivers.

      Arnd