linux-kernel - [PATCH] x86: Disable kernel stack offset randomization for !TSC

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Date:   Sun, 8 Jan 2023 19:42:54 +0000 (GMT)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
cc:     x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] x86: Disable kernel stack offset randomization for !TSC

For x86 kernel stack offset randomization uses the RDTSC instruction, 
which causes an invalid opcode exception with hardware that does not 
implement this instruction:

process '/sbin/init' started with executable stack
invalid opcode: 0000 [#1]
CPU: 0 PID: 1 Comm: init Not tainted 6.1.0-rc4+ #1
EIP: exit_to_user_mode_prepare+0x90/0xe1
Code: 30 02 00 75 ad 0f ba e3 16 73 05 e8 a7 a5 fc ff 0f ba e3 0e 73 05 e8 3e af fc ff a1 c4 c6 51 c0 85 c0 7e 13 8b 0d ac 01 53 c0 <0f> 31 0f b6 c0 31 c1 89 0d ac 01 53 c0 83 3d 30 ed 62 c0 00 75 33
EAX: 00000001 EBX: 00004000 ECX: 00000000 EDX: 000004ff
ESI: c10253c0 EDI: 00000000 EBP: c1027f98 ESP: c1027f8c
DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068 EFLAGS: 00010002
CR0: 80050033 CR2: bfe8659b CR3: 012e0000 CR4: 00000000
Call Trace:
 ? rest_init+0x72/0x72
 syscall_exit_to_user_mode+0x15/0x27
 ret_from_fork+0x10/0x30
EIP: 0xb7f74800
Code: Unable to access opcode bytes at 0xb7f747d6.
EAX: 00000000 EBX: 00000000 ECX: 00000000 EDX: 00000000
ESI: 00000000 EDI: 00000000 EBP: 00000000 ESP: bfe864b0
DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 007b EFLAGS: 00000200
---[ end trace 0000000000000000 ]---
EIP: exit_to_user_mode_prepare+0x90/0xe1
Code: 30 02 00 75 ad 0f ba e3 16 73 05 e8 a7 a5 fc ff 0f ba e3 0e 73 05 e8 3e af fc ff a1 c4 c6 51 c0 85 c0 7e 13 8b 0d ac 01 53 c0 <0f> 31 0f b6 c0 31 c1 89 0d ac 01 53 c0 83 3d 30 ed 62 c0 00 75 33
EAX: 00000001 EBX: 00004000 ECX: 00000000 EDX: 000004ff
ESI: c10253c0 EDI: 00000000 EBP: c1027f98 ESP: c1027f8c
DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068 EFLAGS: 00010002
CR0: 80050033 CR2: b7f747d6 CR3: 012e0000 CR4: 00000000
Kernel panic - not syncing: Fatal exception

Therefore do not offer the option for CPU configurations that do not 
guarantee the presence of this instruction.

Signed-off-by: Maciej W. Rozycki <macro@...am.me.uk>
---
 arch/x86/Kconfig |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

linux-x86-randomize-kstack-offset-tsc.diff
Index: linux-macro/arch/x86/Kconfig
===================================================================
--- linux-macro.orig/arch/x86/Kconfig
+++ linux-macro/arch/x86/Kconfig
@@ -186,7 +186,7 @@ config X86
 	select HAVE_ARCH_USERFAULTFD_WP         if X86_64 && USERFAULTFD
 	select HAVE_ARCH_USERFAULTFD_MINOR	if X86_64 && USERFAULTFD
 	select HAVE_ARCH_VMAP_STACK		if X86_64
-	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
+	select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET	if X86_TSC
 	select HAVE_ARCH_WITHIN_STACK_FRAMES
 	select HAVE_ASM_MODVERSIONS
 	select HAVE_CMPXCHG_DOUBLE