linux-kernel - Re: [PATCH v6 6/6] drivers/node: Show in sysfs node's crypto capabilities

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: <c0007699-61ae-6df3-0675-2ac6ee58a59c@amd.com>
Date:   Fri, 4 Feb 2022 12:49:08 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Limonciello, Mario" <mario.limonciello@....com>,
        Martin Fernandez <martin.fernandez@...ypsium.com>,
        linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, linux-mm@...ck.org,
        tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, ardb@...nel.org,
        dvhart@...radead.org, andy@...radead.org,
        gregkh@...uxfoundation.org, rafael@...nel.org, rppt@...nel.org,
        akpm@...ux-foundation.org, daniel.gutson@...ypsium.com,
        hughsient@...il.com, alex.bazhaniuk@...ypsium.com,
        alison.schofield@...el.com, keescook@...omium.org
Subject: Re: [PATCH v6 6/6] drivers/node: Show in sysfs node's crypto
 capabilities

On 2/4/22 12:00, Borislav Petkov wrote:
> On Fri, Feb 04, 2022 at 11:12:04AM -0600, Tom Lendacky wrote:
>> https://elixir.bootlin.com/linux/latest/source/arch/x86/kernel/process.c#L761
> 
> For those who won't open a browser just to see what he means :), that's
> this snippet:
> 
> void stop_this_cpu(void *dummy):
> 	/*
> 	 * Use wbinvd on processors that support SME. This provides support
> 	 * for performing a successful kexec when going from SME inactive
> 	 * to SME active (or vice-versa). The cache must be cleared so that
> 	 * if there are entries with the same physical address, both with and
> 	 * without the encryption bit, they don't race each other when flushed
> 	 * and potentially end up with the wrong entry being committed to
> 	 * memory.
> 	 */
> 	if (boot_cpu_has(X86_FEATURE_SME))
> 		native_wbinvd();
> 
> 
> Well, we do clear our *representation* of CPUID flags for other features
> - see output of
> 
> $ git grep -E "(setup_)?clear_cpu_cap"
> 
> for examples. We do that for SME even: early_detect_mem_encrypt().
> 
> Which means, since this needs to be "processors that support SME", this
> line should change to:
> 
> 	/* ... test the CPUID bit directly because the machine might've cleared
> 	 * X86_FEATURE_SME due to cmdline options.
> 	 */
> 	if (cpuid_eax(0x8000001f) & BIT(0))
> 		native_wbinvd();
> 
> I'd say...

Yep, and that should be safe. We would have to look at the generated code 
as there can't be any memory stores after the native_wbinvd() and before 
the native_halt().

Thanks,
Tom

>