linux-kernel - Re: [PATCH 26/35] x86/process: Change copy_thread() argument 'arg' to 'stack

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAG48ez0_Ng8Fv4ytLK=Y5ANXiDfBPsFFwfxQTzgmDjU1RNFnDw@mail.gmail.com>
Date:   Mon, 14 Feb 2022 13:33:53 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H . J . Lu" <hjl.tools@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V . Shankar" <ravi.v.shankar@...el.com>,
        Dave Martin <dave.martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        joao.moreira@...el.com, John Allen <john.allen@....com>,
        kcc@...gle.com, eranian@...gle.com,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH 26/35] x86/process: Change copy_thread() argument 'arg' to 'stack_size'

On Sun, Jan 30, 2022 at 10:22 PM Rick Edgecombe
<rick.p.edgecombe@...el.com> wrote:
>
> From: Yu-cheng Yu <yu-cheng.yu@...el.com>
>
> The single call site of copy_thread() passes stack size in 'arg'.  To make
> this clear and in preparation of using this argument for shadow stack
> allocation, change 'arg' to 'stack_size'.  No functional changes.

Actually that name is misleading - the single caller copy_process() indeed does:

retval = copy_thread(clone_flags, args->stack, args->stack_size, p, args->tls);

but the member "stack_size" of "struct kernel_clone_args" can actually
also be a pointer argument given to a kthread, see create_io_thread()
and kernel_thread():

pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
{
  struct kernel_clone_args args = {
    .flags    = ((lower_32_bits(flags) | CLONE_VM |
            CLONE_UNTRACED) & ~CSIGNAL),
    .exit_signal  = (lower_32_bits(flags) & CSIGNAL),
    .stack    = (unsigned long)fn,
    .stack_size  = (unsigned long)arg,
  };

  return kernel_clone(&args);
}

And then in copy_thread(), we have:

kthread_frame_init(frame, sp, arg)


So I'm not sure whether this name change really makes sense, or
whether it just adds to the confusion.