linux-kernel - Re: [PATCH v2 05/39] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states

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Message-ID: <202210031032.82AD49E14@keescook>
Date:   Mon, 3 Oct 2022 10:40:47 -0700
From:   Kees Cook <keescook@...omium.org>
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>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        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>,
        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, rppt@...nel.org,
        jamorris@...ux.microsoft.com, dethoma@...rosoft.com,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH v2 05/39] x86/fpu/xstate: Introduce CET MSR and XSAVES
 supervisor states

On Thu, Sep 29, 2022 at 03:29:02PM -0700, Rick Edgecombe wrote:
> [...]
> xfeatures. So refactor these check's by having XCHECK_SZ() set a bool when
> it actually check's the xfeature. This ends up exceeding 80 chars, but was

Spelling nit through-out all patches: possessive used for plurals. E.g.
the above "check's" instances should be "checks". Please review all the
documentation and commit logs; it shows up a lot. :)

> [...]
> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
> index c8340156bfd2..5e6a4867fd05 100644
> --- a/arch/x86/kernel/fpu/xstate.c
> +++ b/arch/x86/kernel/fpu/xstate.c
> @@ -39,26 +39,26 @@
>   */
>  static const char *xfeature_names[] =
>  {
> -	"x87 floating point registers"	,
> -	"SSE registers"			,
> -	"AVX registers"			,
> -	"MPX bounds registers"		,
> -	"MPX CSR"			,
> -	"AVX-512 opmask"		,
> -	"AVX-512 Hi256"			,
> -	"AVX-512 ZMM_Hi256"		,
> -	"Processor Trace (unused)"	,
> -	"Protection Keys User registers",
> -	"PASID state",
> -	"unknown xstate feature"	,
> -	"unknown xstate feature"	,
> -	"unknown xstate feature"	,
> -	"unknown xstate feature"	,
> -	"unknown xstate feature"	,
> -	"unknown xstate feature"	,
> -	"AMX Tile config"		,
> -	"AMX Tile data"			,
> -	"unknown xstate feature"	,
> +	"x87 floating point registers"			,
> +	"SSE registers"					,
> +	"AVX registers"					,
> +	"MPX bounds registers"				,
> +	"MPX CSR"					,
> +	"AVX-512 opmask"				,
> +	"AVX-512 Hi256"					,
> +	"AVX-512 ZMM_Hi256"				,
> +	"Processor Trace (unused)"			,
> +	"Protection Keys User registers"		,
> +	"PASID state"					,
> +	"Control-flow User registers"			,
> +	"Control-flow Kernel registers (unused)"	,
> +	"unknown xstate feature"			,
> +	"unknown xstate feature"			,
> +	"unknown xstate feature"			,
> +	"unknown xstate feature"			,
> +	"AMX Tile config"				,
> +	"AMX Tile data"					,
> +	"unknown xstate feature"			,

What a strange style. Why not just leave the commas after the " ? Then
these kinds of multi-line updates aren't needed in the future.

> [...]
> -	/*
> -	 * Make *SURE* to add any feature numbers in below if
> -	 * there are "holes" in the xsave state component
> -	 * numbers.
> -	 */
> -	if ((nr < XFEATURE_YMM) ||
> -	    (nr >= XFEATURE_MAX) ||
> -	    (nr == XFEATURE_PT_UNIMPLEMENTED_SO_FAR) ||
> -	    ((nr >= XFEATURE_RSRVD_COMP_11) && (nr <= XFEATURE_RSRVD_COMP_16))) {
> +	if (!chked) {
>  		WARN_ONCE(1, "no structure for xstate: %d\n", nr);
>  		XSTATE_WARN_ON(1);
>  		return false;

This clean-up feels like it should be part of a separate patch, but
okay. :)

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook