linux-kernel - Re: [PATCH 7/7] x86/cet: Add PTRACE interface for CET

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Date:   Thu, 7 Jun 2018 11:32:36 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. J. Lu" <hjl.tools@...il.com>,
        "Shanbhogue, Vedvyas" <vedvyas.shanbhogue@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Oleg Nesterov <oleg@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        mike.kravetz@...cle.com
Subject: Re: [PATCH 7/7] x86/cet: Add PTRACE interface for CET

On Thu, Jun 7, 2018 at 7:42 AM Yu-cheng Yu <yu-cheng.yu@...el.com> wrote:
>
> Add PTRACE interface for CET MSRs.
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> ---
>  arch/x86/include/asm/fpu/regset.h |  7 ++++---
>  arch/x86/kernel/fpu/regset.c      | 41 +++++++++++++++++++++++++++++++++++++++
>  arch/x86/kernel/ptrace.c          | 16 +++++++++++++++
>  include/uapi/linux/elf.h          |  1 +
>  4 files changed, 62 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/fpu/regset.h b/arch/x86/include/asm/fpu/regset.h
> index d5bdffb9d27f..edad0d889084 100644
> --- a/arch/x86/include/asm/fpu/regset.h
> +++ b/arch/x86/include/asm/fpu/regset.h
> @@ -7,11 +7,12 @@
>
>  #include <linux/regset.h>
>
> -extern user_regset_active_fn regset_fpregs_active, regset_xregset_fpregs_active;
> +extern user_regset_active_fn regset_fpregs_active, regset_xregset_fpregs_active,
> +                               cetregs_active;
>  extern user_regset_get_fn fpregs_get, xfpregs_get, fpregs_soft_get,
> -                               xstateregs_get;
> +                               xstateregs_get, cetregs_get;
>  extern user_regset_set_fn fpregs_set, xfpregs_set, fpregs_soft_set,
> -                                xstateregs_set;
> +                                xstateregs_set, cetregs_set;
>
>  /*
>   * xstateregs_active == regset_fpregs_active. Please refer to the comment
> diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
> index bc02f5144b95..7008eb084d36 100644
> --- a/arch/x86/kernel/fpu/regset.c
> +++ b/arch/x86/kernel/fpu/regset.c
> @@ -160,6 +160,47 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
>         return ret;
>  }
>
> +int cetregs_active(struct task_struct *target, const struct user_regset *regset)
> +{
> +#ifdef CONFIG_X86_INTEL_CET
> +       if (target->thread.cet.shstk_enabled || target->thread.cet.ibt_enabled)
> +               return regset->n;
> +#endif
> +       return 0;
> +}
> +
> +int cetregs_get(struct task_struct *target, const struct user_regset *regset,
> +               unsigned int pos, unsigned int count,
> +               void *kbuf, void __user *ubuf)
> +{
> +       struct fpu *fpu = &target->thread.fpu;
> +       struct cet_user_state *cetregs;
> +
> +       if (!boot_cpu_has(X86_FEATURE_SHSTK))
> +               return -ENODEV;

This whole series has a boot_cpu_has, static_cpu_has, and
cpu_feature_enabled all over.  Please settle on just one, preferably
static_cpu_has.

> +
> +       cetregs = get_xsave_addr(&fpu->state.xsave, XFEATURE_MASK_SHSTK_USER);
> +
> +       fpu__prepare_read(fpu);
> +       return user_regset_copyout(&pos, &count, &kbuf, &ubuf, cetregs, 0, -1);
> +}
> +
> +int cetregs_set(struct task_struct *target, const struct user_regset *regset,
> +                 unsigned int pos, unsigned int count,
> +                 const void *kbuf, const void __user *ubuf)
> +{
> +       struct fpu *fpu = &target->thread.fpu;
> +       struct cet_user_state *cetregs;
> +
> +       if (!boot_cpu_has(X86_FEATURE_SHSTK))
> +               return -ENODEV;
> +
> +       cetregs = get_xsave_addr(&fpu->state.xsave, XFEATURE_MASK_SHSTK_USER);
> +
> +       fpu__prepare_write(fpu);
> +       return user_regset_copyin(&pos, &count, &kbuf, &ubuf, cetregs, 0, -1);

Is this called for core dumping on current?  If so, please make sure
it's correct.  (I think it is for get but maybe not for set.)