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-next>] [day] [month] [year] [list]
Date: Fri, 26 Jan 2024 12:01:01 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Cc: x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Kai Huang <kai.huang@...el.com>,
	Sean Christopherson <seanjc@...gle.com>
Subject: [PATCHv4] x86/trampoline: Bypass compat mode in trampoline_start64() if not needed

The trampoline_start64() vector is used when a secondary CPU starts in
64-bit mode. The current implementation directly enters compatibility
mode. It is necessary to disable paging and re-enable it in the correct
paging mode: either 4- or 5-level, depending on the configuration.

The X86S[1] ISA does not support compatibility mode in ring 0, and
paging cannot be disabled.

The trampoline_start64() function is reworked to only enter compatibility
mode if it is necessary to change the paging mode. If the CPU is already
in the desired paging mode, it will proceed in long mode.

This change will allow a secondary CPU to boot on an X86S machine as
long as the CPU is already in the correct paging mode.

In the future, there will be a mechanism to switch between paging modes
without disabling paging.

[1] https://www.intel.com/content/www/us/en/developer/articles/technical/envisioning-future-simplified-architecture.html

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Reviewed-by: Andi Kleen <ak@...ux.intel.com>
Reviewed-by: Kai Huang <kai.huang@...el.com>
Cc: Sean Christopherson <seanjc@...gle.com>

---
 v4:
  - Establish CS on jumping to tr_start (Andi);
 v3:
  - tr_cr4 is 32-bit, use 32-bit XOR to access it (Sean).
  - Use 32-bit TEST instead of AND to check if LA57 different between
    CR4 and tr_cr4 (Sean).
 v2:
  - Fix build with GCC;
---
 arch/x86/realmode/rm/trampoline_64.S | 33 +++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S
index c9f76fae902e..14d9c7daf90f 100644
--- a/arch/x86/realmode/rm/trampoline_64.S
+++ b/arch/x86/realmode/rm/trampoline_64.S
@@ -37,13 +37,15 @@
 	.text
 	.code16
 
-.macro LOCK_AND_LOAD_REALMODE_ESP lock_pa=0
+.macro LOCK_AND_LOAD_REALMODE_ESP lock_pa=0 lock_rip=0
 	/*
 	 * Make sure only one CPU fiddles with the realmode stack
 	 */
 .Llock_rm\@:
 	.if \lock_pa
         lock btsl       $0, pa_tr_lock
+	.elseif \lock_rip
+        lock btsl       $0, tr_lock(%rip)
 	.else
         lock btsl       $0, tr_lock
 	.endif
@@ -220,6 +222,35 @@ SYM_CODE_START(trampoline_start64)
 	lidt	tr_idt(%rip)
 	lgdt	tr_gdt64(%rip)
 
+	/* Check if paging mode has to be changed */
+	movq	%cr4, %rax
+	xorl	tr_cr4(%rip), %eax
+	testl	$X86_CR4_LA57, %eax
+	jnz	.L_switch_paging
+
+	/* Paging mode is correct proceed in 64-bit mode */
+
+	LOCK_AND_LOAD_REALMODE_ESP lock_rip=1
+
+	movw	$__KERNEL_DS, %dx
+	movl	%edx, %ss
+	addl	$pa_real_mode_base, %esp
+	movl	%edx, %ds
+	movl	%edx, %es
+	movl	%edx, %fs
+	movl	%edx, %gs
+
+	movl	$pa_trampoline_pgd, %eax
+	movq	%rax, %cr3
+
+	pushq	$__KERNEL_CS
+	pushq	tr_start(%rip)
+	lretq
+.L_switch_paging:
+	/*
+	 * To switch between 4- and 5-level paging modes, it is necessary
+	 * to disable paging. This must be done in the compatibility mode.
+	 */
 	ljmpl	*tr_compat(%rip)
 SYM_CODE_END(trampoline_start64)
 
-- 
2.43.0


Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ