linux-kernel - Re: [PATCH v7 40/41] x86/shstk: Add ARCH_SHSTK

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Message-ID: <ZAyaIJFhSh0QyVq0@zn.tnic>
Date:   Sat, 11 Mar 2023 16:11:28 +0100
From:   Borislav Petkov <bp@...en8.de>
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>,
        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>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        John Allen <john.allen@....com>, kcc@...gle.com,
        eranian@...gle.com, rppt@...nel.org, jamorris@...ux.microsoft.com,
        dethoma@...rosoft.com, akpm@...ux-foundation.org,
        Andrew.Cooper3@...rix.com, christina.schimpe@...el.com,
        david@...hat.com, debug@...osinc.com,
        Mike Rapoport <rppt@...ux.ibm.com>
Subject: Re: [PATCH v7 40/41] x86/shstk: Add ARCH_SHSTK_UNLOCK

On Mon, Feb 27, 2023 at 02:29:56PM -0800, Rick Edgecombe wrote:
> From: Mike Rapoport <rppt@...ux.ibm.com>
> 
> Userspace loaders may lock features before a CRIU restore operation has
> the chance to set them to whatever state is required by the process
> being restored. Allow a way for CRIU to unlock features. Add it as an
> arch_prctl() like the other shadow stack operations, but restrict it being
> called by the ptrace arch_pctl() interface.
> 
> Tested-by: Pengfei Xu <pengfei.xu@...el.com>
> Tested-by: John Allen <john.allen@....com>
> Tested-by: Kees Cook <keescook@...omium.org>
> Acked-by: Mike Rapoport (IBM) <rppt@...nel.org>

That tag is kinda implicit here. Unless he doesn't ACK his own patch.
:-P

> Reviewed-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> [Merged into recent API changes, added commit log and docs]
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>

...

> diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
> index 2faf9b45ac72..3197ff824809 100644
> --- a/arch/x86/kernel/shstk.c
> +++ b/arch/x86/kernel/shstk.c
> @@ -451,9 +451,14 @@ long shstk_prctl(struct task_struct *task, int option, unsigned long features)
>  		return 0;
>  	}
>  
> -	/* Don't allow via ptrace */
> -	if (task != current)
> +	/* Only allow via ptrace */
> +	if (task != current) {

Is that the only case? task != current means ptrace and there's no other
way to do this from userspace?

Isn't there some flag which says that task is ptraced? I think we should
check that one too...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette