linux-kernel - Re: [PATCH v1 1/4] lib: introduce copy_struct_from

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Message-ID: <CAHk-=wjFeNjhtUxQ8npmXORz5RLQU7B_3wD=45eug1+MXnuYvA@mail.gmail.com>
Date:   Wed, 25 Sep 2019 10:10:37 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Aleksa Sarai <cyphar@...har.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Christian Brauner <christian@...uner.io>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Al Viro <viro@...iv.linux.org.uk>,
        GNU C Library <libc-alpha@...rceware.org>,
        Linux API <linux-api@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/4] lib: introduce copy_struct_from_user() helper

On Wed, Sep 25, 2019 at 10:00 AM Aleksa Sarai <cyphar@...har.com> wrote:
>
> +int is_zeroed_user(const void __user *from, size_t size)

I like how you've done this, but it's buggy and only works on 64-bit.

All the "u64" and "8" cases need to be "unsigned long" and
"sizeof(unsigned long)".

Part of that requirement is:

> +               unsafe_get_user(val, (u64 __user *) from, err_fault);

This part works fine - although 64-bit accesses migth be much more
expensive and the win of unrolling might not be sufficient - but:

> +               if (align) {
> +                       /* @from is unaligned. */
> +                       val &= ~aligned_byte_mask(align);
> +                       align = 0;
> +               }

This part fundamentally only works on 'unsigned long'.

         Linus