linux-kernel - [tip: x86/asm] x86/kexec: Invalidate GDT/IDT from relocate

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: <174428357481.31282.17425113277917466268.tip-bot2@tip-bot2>
Date: Thu, 10 Apr 2025 11:12:54 -0000
From: "tip-bot2 for David Woodhouse" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: David Woodhouse <dwmw@...zon.co.uk>, Ingo Molnar <mingo@...nel.org>,
 Brian Gerst <brgerst@...il.com>, Juergen Gross <jgross@...e.com>,
 "H. Peter Anvin" <hpa@...or.com>,
 Linus Torvalds <torvalds@...ux-foundation.org>,
 Josh Poimboeuf <jpoimboe@...hat.com>, Kees Cook <keescook@...omium.org>,
 Ard Biesheuvel <ardb@...nel.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/asm] x86/kexec: Invalidate GDT/IDT from relocate_kernel()
 instead of earlier

The following commit has been merged into the x86/asm branch of tip:

Commit-ID:     de085ddd493bccb77a3ec1b99ae7466133540f4d
Gitweb:        https://git.kernel.org/tip/de085ddd493bccb77a3ec1b99ae7466133540f4d
Author:        David Woodhouse <dwmw@...zon.co.uk>
AuthorDate:    Wed, 26 Mar 2025 14:16:03 
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Thu, 10 Apr 2025 12:17:14 +02:00

x86/kexec: Invalidate GDT/IDT from relocate_kernel() instead of earlier

Reduce the window during which exceptions are unhandled, by leaving the
GDT/IDT in place all the way into the relocate_kernel() function, until
the moment that %cr3 gets replaced.

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Ard Biesheuvel <ardb@...nel.org>
Link: https://lore.kernel.org/r/20250326142404.256980-4-dwmw2@infradead.org
---
 arch/x86/kernel/machine_kexec_64.c   | 10 ++--------
 arch/x86/kernel/relocate_kernel_64.S |  9 +++++++--
 2 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index ecb0da5..949c9e4 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -434,16 +434,10 @@ void __nocfi machine_kexec(struct kimage *image)
 	 * with from a table in memory.  At no other time is the
 	 * descriptor table in memory accessed.
 	 *
-	 * I take advantage of this here by force loading the
-	 * segments, before I zap the gdt with an invalid value.
+	 * Take advantage of this here by force loading the segments,
+	 * before the GDT is zapped with an invalid value.
 	 */
 	load_segments();
-	/*
-	 * The gdt & idt are now invalid.
-	 * If you want to load them you must set up your own idt & gdt.
-	 */
-	native_idt_invalidate();
-	native_gdt_invalidate();
 
 	/* now call it */
 	image->start = relocate_kernel_ptr((unsigned long)image->head,
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 8808cfc..3062cb3 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -79,8 +79,13 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
 	pushq %r15
 	pushf
 
-	/* zero out flags, and disable interrupts */
-	pushq $0
+	/* Invalidate GDT/IDT, zero out flags */
+	pushq	$0
+	pushq	$0
+
+	lidt	(%rsp)
+	lgdt	(%rsp)
+	addq	$8, %rsp
 	popfq
 
 	/* Switch to the identity mapped page tables */