Merge tag 'x86-core-2023-08-30-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 core updates from Thomas Gleixner:

- Prevent kprobes on compiler generated CFI checking code.

The compiler generates an instruction sequence for indirect call
checks. If this sequence is modified with a kprobe, then the check
fails. So the instructions must be protected against probing.

- A few minor cleanups for the SMP code

* tag 'x86-core-2023-08-30-v2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/kprobes: Prohibit probing on compiler generated CFI checking code
x86/smpboot: Change smp_store_boot_cpu_info() to static
x86/smp: Remove a non-existent function declaration
x86/smpboot: Remove a stray comment about CPU hotplug

arch/x86/include/asm/smp.h

···
 void native_smp_send_reschedule(int cpu);
 void native_send_call_func_ipi(const struct cpumask *mask);
 void native_send_call_func_single_ipi(int cpu);
-void x86_idle_thread_init(unsigned int cpu, struct task_struct *idle);
 
 bool smp_park_other_cpus_in_init(void);
-
-void smp_store_boot_cpu_info(void);
 void smp_store_cpu_info(int id);
 
 asmlinkage __visible void smp_reboot_interrupt(void);

arch/x86/kernel/kprobes/core.c

···
 #include <linux/vmalloc.h>
 #include <linux/pgtable.h>
 #include <linux/set_memory.h>
+#include <linux/cfi.h>
 
 #include <asm/text-patching.h>
 #include <asm/cacheflush.h>
···
 #endif
 		addr += insn.length;
 	}
+	if (IS_ENABLED(CONFIG_CFI_CLANG)) {
+		/*
+		 * The compiler generates the following instruction sequence
+		 * for indirect call checks and cfi.c decodes this;
+		 *
+		 *   movl    -<id>, %r10d       ; 6 bytes
+		 *   addl    -4(%reg), %r10d    ; 4 bytes
+		 *   je      .Ltmp1             ; 2 bytes
+		 *   ud2                        ; <- regs->ip
+		 *   .Ltmp1:
+		 *
+		 * Also, these movl and addl are used for showing expected
+		 * type. So those must not be touched.
+		 */
+		__addr = recover_probed_instruction(buf, addr);
+		if (!__addr)
+			return 0;
 
+		if (insn_decode_kernel(&insn, (void *)__addr) < 0)
+			return 0;
+
+		if (insn.opcode.value == 0xBA)
+			offset = 12;
+		else if (insn.opcode.value == 0x3)
+			offset = 6;
+		else
+			goto out;
+
+		/* This movl/addl is used for decoding CFI. */
+		if (is_cfi_trap(addr + offset))
+			return 0;
+	}
+
+out:
 	return (addr == paddr);
 }
 

arch/x86/kernel/smpboot.c

···
 	return 0;
 }
 
-void __init smp_store_boot_cpu_info(void)
+static void __init smp_store_boot_cpu_info(void)
 {
 	int id = 0; /* CPU 0 */
 	struct cpuinfo_x86 *c = &cpu_data(id);
···
 	idle_task_exit();
 
 	cpuhp_ap_report_dead();
-	/*
-	 * With physical CPU hotplug, we should halt the cpu
-	 */
+
 	local_irq_disable();
 }
 

include/linux/cfi.h

···
 {
 	return report_cfi_failure(regs, addr, NULL, 0);
 }
+#endif /* CONFIG_CFI_CLANG */
 
 #ifdef CONFIG_ARCH_USES_CFI_TRAPS
 bool is_cfi_trap(unsigned long addr);
+#else
+static inline bool is_cfi_trap(unsigned long addr) { return false; }
 #endif
-#endif /* CONFIG_CFI_CLANG */
 
 #ifdef CONFIG_MODULES
 #ifdef CONFIG_ARCH_USES_CFI_TRAPS