linux-kernel - Re: [PATCH v7 12/14] x86/vsyscall/64: Fixup shadow stack and branch tracking for vsyscall

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Date:   Thu, 6 Jun 2019 13:27:43 -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: [PATCH v7 12/14] x86/vsyscall/64: Fixup shadow stack and branch
 tracking for vsyscall

On Thu, Jun 6, 2019 at 1:17 PM Yu-cheng Yu <yu-cheng.yu@...el.com> wrote:
>
> When emulating a RET, also unwind the task's shadow stack and cancel
> the current branch tracking status.
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> ---
>  arch/x86/entry/vsyscall/vsyscall_64.c | 28 +++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
>
> diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
> index d9d81ad7a400..6869ef9d1e8b 100644
> --- a/arch/x86/entry/vsyscall/vsyscall_64.c
> +++ b/arch/x86/entry/vsyscall/vsyscall_64.c
> @@ -38,6 +38,8 @@
>  #include <asm/fixmap.h>
>  #include <asm/traps.h>
>  #include <asm/paravirt.h>
> +#include <asm/fpu/xstate.h>
> +#include <asm/fpu/types.h>
>
>  #define CREATE_TRACE_POINTS
>  #include "vsyscall_trace.h"
> @@ -92,6 +94,30 @@ static int addr_to_vsyscall_nr(unsigned long addr)
>         return nr;
>  }
>
> +void fixup_shstk(void)
> +{
> +#ifdef CONFIG_X86_INTEL_SHADOW_STACK_USER
> +       u64 r;
> +
> +       if (current->thread.cet.shstk_enabled) {
> +               rdmsrl(MSR_IA32_PL3_SSP, r);
> +               wrmsrl(MSR_IA32_PL3_SSP, r + 8);
> +       }
> +#endif
> +}
> +
> +void fixup_ibt(void)
> +{
> +#ifdef CONFIG_X86_INTEL_BRANCH_TRACKING_USER
> +       u64 r;
> +
> +       if (current->thread.cet.ibt_enabled) {
> +               rdmsrl(MSR_IA32_U_CET, r);
> +               wrmsrl(MSR_IA32_U_CET, r & ~MSR_IA32_CET_WAIT_ENDBR);
> +       }
> +#endif
> +}

These should be static.

But please just inline them directly in their one call site.  The code
will be a lot easier to understand.

--Andy