linux-kernel - Re: [PATCH 0/3] Resolve problems with kexec identity mapping

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Message-ID: <20240709164620.GLZo1pXPiG42JH4ylN@fat_crate.local>
Date: Tue, 9 Jul 2024 18:46:20 +0200
From: Borislav Petkov <bp@...en8.de>
To: Steve Wahl <steve.wahl@....com>
Cc: Ard Biesheuvel <ardb@...nel.org>, Ashish Kalra <ashish.kalra@....com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Pavin Joseph <me@...injoseph.com>,
	Eric Hagberg <ehagberg@...il.com>,
	Simon Horman <horms@...ge.net.au>,
	Eric Biederman <ebiederm@...ssion.com>,
	Dave Young <dyoung@...hat.com>, Sarah Brofeldt <srhb@....dk>,
	Russ Anderson <rja@....com>, Dimitri Sivanich <sivanich@....com>,
	Hou Wenlong <houwenlong.hwl@...group.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Baoquan He <bhe@...hat.com>, Yuntao Wang <ytcoode@...il.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, Joerg Roedel <jroedel@...e.de>,
	Michael Roth <michael.roth@....com>
Subject: Re: [PATCH 0/3] Resolve problems with kexec identity mapping

On Tue, Jul 09, 2024 at 10:07:48AM -0500, Steve Wahl wrote:
> I think perhaps the cover letter was also too verbose on the history
> and unintentionally hid the information necesary to understand the
> situation.  I will try to make it more concise.

Thanks.

And while we're at it, I think we should do this too.

Which should actually fix your issue too.

---
diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index cd44e120fe53..a838cad72532 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -484,6 +484,15 @@ static bool early_snp_init(struct boot_params *bp)
 {
 	struct cc_blob_sev_info *cc_info;
 
+	/*
+	 * Bail out if not running on a hypervisor (HV). If the HV
+	 * doesn't set the bit, that's an easy SEV-* guest DOS but that
+	 * HV has then bigger problems: the SEV-* guest simply won't
+	 * start.
+	 */
+	if (!(native_cpuid_ecx(1) & BIT(31)))
+		return false;
+
 	if (!bp)
 		return false;
 

-- 
Regards/Gruss,
    Boris.

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