linux-kernel - Re: [RFC PATCH 2/3] Introduce arch_prctl(ARCH_X86_CET_MARK_LEGACY

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 for Android: free password hash cracker in your pocket

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

Message-ID: <CALCETrVvbbCWMPo7v5eYgTocaxRQPHerJ=CRjWscGxgb6QjOFA@mail.gmail.com>
Date:   Sat, 29 Jun 2019 16:43:18 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        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>, Jann Horn <jannh@...gle.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>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>
Subject: Re: [RFC PATCH 2/3] Introduce arch_prctl(ARCH_X86_CET_MARK_LEGACY_CODE)

> On Jun 28, 2019, at 12:41 PM, Yu-cheng Yu <yu-cheng.yu@...el.com> wrote:
>
> The CET legacy code bitmap covers the whole user-mode address space and is
> located at the top of the user-mode address space.  It is allocated only
> when the first time arch_prctl(ARCH_X86_MARK_LEGACY_CODE) is called from
> an application.
>
> Introduce:
>
> arch_prctl(ARCH_X86_MARK_LEGACY_CODE, unsigned long *buf)
>    Mark an address range as IBT legacy code.

How about defining a struct for this?

The change log should discuss where the bitmap goes and how it’s allocated.

> +static int alloc_bitmap(void)
> +{
> +    unsigned long addr;
> +    u64 msr_ia32_u_cet;
> +
> +    addr = do_mmap_locked(NULL, IBT_BITMAP_ADDR, IBT_BITMAP_SIZE,
> +                  PROT_READ | PROT_WRITE,
> +                  MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED_NOREPLACE,
> +                  VM_IBT | VM_NORESERVE, NULL);
> +
> +    if (IS_ERR((void *)addr))
> +        return addr;
> +
> +    current->thread.cet.ibt_bitmap_addr = addr;

addr is a constant. Why are you storing it?  If it ends up not being
constant, you should wire up mremap like the vDSO does.


> +static int set_user_bits(unsigned long __user *buf, unsigned long buf_size,
> +             unsigned long start_bit, unsigned long end_bit, unsigned long set)
> +{
> +    unsigned long start_ul, end_ul, total_ul;
> +    int i, j, r;
> +
> +    if (round_up(end_bit, BITS_PER_BYTE) / BITS_PER_BYTE > buf_size)
> +        end_bit = buf_size * BITS_PER_BYTE - 1;
> +
> +    start_ul = start_bit / BITS_PER_LONG;
> +    end_ul = end_bit / BITS_PER_LONG;
> +    total_ul = (end_ul - start_ul + 1);
> +
> +    i = start_bit % BITS_PER_LONG;
> +    j = end_bit % BITS_PER_LONG;
> +
> +    r = 0;
> +    put_user_try {

put_user_try is obsolete.  Just use get_user(), etc.

Also, I must be missing something fundamental, because this series
claims that user code can't write directly to the bitmap.  This means
that this entire function shouldn't work at all.