Messages in this thread Patch in this message | | | Date | Sun, 8 Jan 2023 21:26:11 +0000 (GMT) | From | "Maciej W. Rozycki" <> | Subject | [PATCH v2] x86: Disable kernel stack offset randomization for !TSC |
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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 use randomization where the CPU does not have the TSC feature.
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk> --- Changes from v1:
- Disable randomization at run time rather than in configuration. --- arch/x86/include/asm/entry-common.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
linux-x86-randomize-kstack-offset-tsc.diff Index: linux-macro/arch/x86/include/asm/entry-common.h =================================================================== --- linux-macro.orig/arch/x86/include/asm/entry-common.h +++ linux-macro/arch/x86/include/asm/entry-common.h @@ -5,6 +5,7 @@ #include <linux/randomize_kstack.h> #include <linux/user-return-notifier.h> +#include <asm/cpufeature.h> #include <asm/nospec-branch.h> #include <asm/io_bitmap.h> #include <asm/fpu/api.h> @@ -85,7 +86,8 @@ static inline void arch_exit_to_user_mod * Therefore, final stack offset entropy will be 5 (x86_64) or * 6 (ia32) bits. */ - choose_random_kstack_offset(rdtsc() & 0xFF); + if (cpu_feature_enabled(X86_FEATURE_TSC)) + choose_random_kstack_offset(rdtsc() & 0xFF); } #define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare
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