Re: [PATCH v5 04/27] x86/fpu/xstate: Add XSAVES system states for shadow stack

From: Andy Lutomirski <luto@amacapital.net>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Balbir Singh <bsingharora@gmail.com>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Eugene Syromiatnikov <esyr@redhat.com>,
	Florian Weimer <fweimer@redhat.com>,
	"H. J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Kees Cook <keescook@chromium.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Nadav Amit <nadav.amit@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
	Peter Zijlstra <peterz@infradead.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	"Shanbhogue, Vedvyas" <vedvyas.shanbhogue@intel.com>
Subject: Re: [PATCH v5 04/27] x86/fpu/xstate: Add XSAVES system states for shadow stack
Date: Thu, 8 Nov 2018 12:46:29 -0800	[thread overview]
Message-ID: <CALCETrVAe8R=crVHoD5QmbN-gAW+V-Rwkwe4kQP7V7zQm9TM=Q@mail.gmail.com> (raw)
In-Reply-To: <20181011151523.27101-5-yu-cheng.yu@intel.com>

On Thu, Oct 11, 2018 at 8:20 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>
> Intel Control-flow Enforcement Technology (CET) introduces the
> following MSRs into the XSAVES system states.
>
>     IA32_U_CET (user-mode CET settings),
>     IA32_PL3_SSP (user-mode shadow stack),
>     IA32_PL0_SSP (kernel-mode shadow stack),
>     IA32_PL1_SSP (ring-1 shadow stack),
>     IA32_PL2_SSP (ring-2 shadow stack).
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> ---
>  arch/x86/include/asm/fpu/types.h            | 22 +++++++++++++++++++++
>  arch/x86/include/asm/fpu/xstate.h           |  4 +++-
>  arch/x86/include/uapi/asm/processor-flags.h |  2 ++
>  arch/x86/kernel/fpu/xstate.c                | 10 ++++++++++
>  4 files changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
> index 202c53918ecf..e55d51d172f1 100644
> --- a/arch/x86/include/asm/fpu/types.h
> +++ b/arch/x86/include/asm/fpu/types.h
> @@ -114,6 +114,9 @@ enum xfeature {
>         XFEATURE_Hi16_ZMM,
>         XFEATURE_PT_UNIMPLEMENTED_SO_FAR,
>         XFEATURE_PKRU,
> +       XFEATURE_RESERVED,
> +       XFEATURE_SHSTK_USER,
> +       XFEATURE_SHSTK_KERNEL,
>
>         XFEATURE_MAX,
>  };
> @@ -128,6 +131,8 @@ enum xfeature {
>  #define XFEATURE_MASK_Hi16_ZMM         (1 << XFEATURE_Hi16_ZMM)
>  #define XFEATURE_MASK_PT               (1 << XFEATURE_PT_UNIMPLEMENTED_SO_FAR)
>  #define XFEATURE_MASK_PKRU             (1 << XFEATURE_PKRU)
> +#define XFEATURE_MASK_SHSTK_USER       (1 << XFEATURE_SHSTK_USER)
> +#define XFEATURE_MASK_SHSTK_KERNEL     (1 << XFEATURE_SHSTK_KERNEL)
>
>  #define XFEATURE_MASK_FPSSE            (XFEATURE_MASK_FP | XFEATURE_MASK_SSE)
>  #define XFEATURE_MASK_AVX512           (XFEATURE_MASK_OPMASK \
> @@ -229,6 +234,23 @@ struct pkru_state {
>         u32                             pad;
>  } __packed;
>
> +/*
> + * State component 11 is Control flow Enforcement user states
> + */
> +struct cet_user_state {
> +       u64 u_cet;      /* user control flow settings */
> +       u64 user_ssp;   /* user shadow stack pointer */
> +} __packed;
> +
> +/*
> + * State component 12 is Control flow Enforcement kernel states
> + */
> +struct cet_kernel_state {
> +       u64 kernel_ssp; /* kernel shadow stack */
> +       u64 pl1_ssp;    /* ring-1 shadow stack */
> +       u64 pl2_ssp;    /* ring-2 shadow stack */
> +} __packed;
> +

Why are these __packed?  It seems like it'll generate bad code for no
obvious purpose.