linux-kernel - [PATCHv9.1 05/17] x86/kexec: Keep CR4.MCE set during kexec for TDX guest

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20240403152342.918612-1-kirill.shutemov@linux.intel.com>
Date: Wed,  3 Apr 2024 18:23:42 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: kirill.shutemov@...ux.intel.com
Cc: adrian.hunter@...el.com,
	ashish.kalra@....com,
	bhe@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	elena.reshetova@...el.com,
	jun.nakajima@...el.com,
	kai.huang@...el.com,
	kexec@...ts.infradead.org,
	linux-coco@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	mingo@...hat.com,
	peterz@...radead.org,
	rafael@...nel.org,
	rick.p.edgecombe@...el.com,
	sathyanarayanan.kuppuswamy@...ux.intel.com,
	seanjc@...gle.com,
	tglx@...utronix.de,
	thomas.lendacky@....com
Subject: [PATCHv9.1 05/17] x86/kexec: Keep CR4.MCE set during kexec for TDX guest

Depending on setup, TDX guests might be allowed to clear CR4.MCE.
Attempt to clear it leads to #VE.

Use alternatives to keep the flag during kexec for TDX guests.

The change doesn't affect non-TDX-guest environments.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---

v9.1:
  - Preserve CR4.MCE instead of setting it unconditionally.

---
 arch/x86/kernel/relocate_kernel_64.S | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 56cab1bb25f5..8e2037d78a1f 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -5,6 +5,8 @@
  */
 
 #include <linux/linkage.h>
+#include <linux/stringify.h>
+#include <asm/alternative.h>
 #include <asm/page_types.h>
 #include <asm/kexec.h>
 #include <asm/processor-flags.h>
@@ -145,11 +147,17 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	 * Set cr4 to a known state:
 	 *  - physical address extension enabled
 	 *  - 5-level paging, if it was enabled before
+	 *  - Machine check exception on TDX guest, if it was enabled before.
+	 *    Clearing MCE might not allowed in TDX guests, depending on setup.
 	 */
 	movl	$X86_CR4_PAE, %eax
 	testq	$X86_CR4_LA57, %r13
 	jz	1f
 	orl	$X86_CR4_LA57, %eax
+1:
+	testq	$X86_CR4_MCE, %r13
+	jz	1f
+	ALTERNATIVE "", __stringify(orl $X86_CR4_MCE, %eax), X86_FEATURE_TDX_GUEST
 1:
 	movq	%rax, %cr4
 
-- 
2.43.0