linux-kernel - Re: [PATCHv8 04/17] x86/cpu: Defer CR pinning setup until after EFI initialization

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <080df169-0f47-40ea-b7b3-4d1a35bee151@intel.com>
Date: Tue, 1 Jul 2025 12:03:01 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Andy Lutomirski
	<luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar
	<mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, "H. Peter Anvin"
	<hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>, Ard Biesheuvel
	<ardb@...nel.org>, "Paul E. McKenney" <paulmck@...nel.org>, Josh Poimboeuf
	<jpoimboe@...nel.org>, Xiongwei Song <xiongwei.song@...driver.com>, Xin Li
	<xin3.li@...el.com>, "Mike Rapoport (IBM)" <rppt@...nel.org>, Brijesh Singh
	<brijesh.singh@....com>, Michael Roth <michael.roth@....com>, Tony Luck
	<tony.luck@...el.com>, Alexey Kardashevskiy <aik@....com>, Alexander Shishkin
	<alexander.shishkin@...ux.intel.com>
CC: Jonathan Corbet <corbet@....net>, Ingo Molnar <mingo@...nel.org>, "Pawan
 Gupta" <pawan.kumar.gupta@...ux.intel.com>, Daniel Sneddon
	<daniel.sneddon@...ux.intel.com>, Kai Huang <kai.huang@...el.com>, "Sandipan
 Das" <sandipan.das@....com>, Breno Leitao <leitao@...ian.org>, Rick Edgecombe
	<rick.p.edgecombe@...el.com>, Alexei Starovoitov <ast@...nel.org>, Hou Tao
	<houtao1@...wei.com>, Juergen Gross <jgross@...e.com>, Vegard Nossum
	<vegard.nossum@...cle.com>, Kees Cook <kees@...nel.org>, Eric Biggers
	<ebiggers@...gle.com>, Jason Gunthorpe <jgg@...pe.ca>, "Masami Hiramatsu
 (Google)" <mhiramat@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
	Luis Chamberlain <mcgrof@...nel.org>, Yuntao Wang <ytcoode@...il.com>,
	"Rasmus Villemoes" <linux@...musvillemoes.dk>, Christophe Leroy
	<christophe.leroy@...roup.eu>, Tejun Heo <tj@...nel.org>, Changbin Du
	<changbin.du@...wei.com>, Huang Shijie <shijie@...amperecomputing.com>,
	"Geert Uytterhoeven" <geert+renesas@...der.be>, Namhyung Kim
	<namhyung@...nel.org>, Arnaldo Carvalho de Melo <acme@...hat.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-efi@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCHv8 04/17] x86/cpu: Defer CR pinning setup until after EFI
 initialization

On 7/1/2025 2:58 AM, Kirill A. Shutemov wrote:
> From: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> 
> In order to map the EFI runtime services, set_virtual_address_map()
> needs to be called, which resides in the lower half of the address
> space. This means that LASS needs to be temporarily disabled around
> this call. This can only be done before the CR pinning is set up.
> 
> Move CR pinning setup behind the EFI initialization.
> 
> Wrapping efi_enter_virtual_mode() into lass_disable/enable_enforcement()

I believe this should be lass_stac()/clac() since we reverted to the
original naming.

> is not enough because AC flag gates data accesses, but not instruction
> fetch. Clearing the CR4 bit is required.
> 
> Signed-off-by: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Suggested-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  arch/x86/kernel/cpu/common.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 4f430be285de..9918121e0adc 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -2081,7 +2081,6 @@ static __init void identify_boot_cpu(void)
>  	enable_sep_cpu();
>  #endif
>  	cpu_detect_tlb(&boot_cpu_data);
> -	setup_cr_pinning();
>  
>  	tsx_init();
>  	tdx_init();
> @@ -2532,10 +2531,14 @@ void __init arch_cpu_finalize_init(void)
>  
>  	/*
>  	 * This needs to follow the FPU initializtion, since EFI depends on it.
> +	 *
> +	 * EFI twiddles CR4.LASS. Do it before CR pinning.
>  	 */
>  	if (efi_enabled(EFI_RUNTIME_SERVICES))
>  		efi_enter_virtual_mode();
>  
> +	setup_cr_pinning();
> +

Instead of EFI toggling CR4.LASS, why not defer the first LASS
activation itself?

i.e.

	if (efi_enabled(EFI_RUNTIME_SERVICES))
		efi_enter_virtual_mode();

	setup_lass();

	setup_cr_pinning();


This way, we can avoid the following patch (#5) altogether.