x86/split_lock: Provide handle_guest_split_lock()

Without at least minimal handling for split lock detection induced #AC, VMX will just run into the same problem as the VMWare hypervisor, which was reported by Kenneth. It will inject the #AC blindly into the guest whether the guest is prepared or not. Provide a function for guest mode which acts depending on the host SLD mode. If mode == sld_warn, treat it like user space, i.e. emit a warning, disable SLD and mark the task accordingly. Otherwise force SIGBUS. [ bp: Add a !CPU_SUP_INTEL stub for handle_guest_split_lock(). ] Signed-off-by: Thomas Gleixner <[email protected]> Signed-off-by: Borislav Petkov <[email protected]> Acked-by: Paolo Bonzini <[email protected]> Link: https://lkml.kernel.org/r/[email protected] Link: https://lkml.kernel.org/r/[email protected]
ambv · Apr 11, 2020 · d7e94db · d7e94db
1 parent 5b8b9d0
commit d7e94db
Show file tree

Hide file tree

Showing 2 changed files with 34 additions and 5 deletions.
diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
@@ -44,12 +44,18 @@ unsigned int x86_stepping(unsigned int sig);
 extern void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c);
 extern void switch_to_sld(unsigned long tifn);
 extern bool handle_user_split_lock(struct pt_regs *regs, long error_code);
+extern bool handle_guest_split_lock(unsigned long ip);
 #else
 static inline void __init cpu_set_core_cap_bits(struct cpuinfo_x86 *c) {}
 static inline void switch_to_sld(unsigned long tifn) {}
 static inline bool handle_user_split_lock(struct pt_regs *regs, long error_code)
 {
 	return false;
 }
+
+static inline bool handle_guest_split_lock(unsigned long ip)
+{
+	return false;
+}
 #endif
 #endif /* _ASM_X86_CPU_H */
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
@@ -21,6 +21,7 @@
 #include <asm/elf.h>
 #include <asm/cpu_device_id.h>
 #include <asm/cmdline.h>
+#include <asm/traps.h>
 
 #ifdef CONFIG_X86_64
 #include <linux/topology.h>
@@ -1066,13 +1067,10 @@ static void split_lock_init(void)
 	split_lock_verify_msr(sld_state != sld_off);
 }
 
-bool handle_user_split_lock(struct pt_regs *regs, long error_code)
+static void split_lock_warn(unsigned long ip)
 {
-	if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal)
-		return false;
-
 	pr_warn_ratelimited("#AC: %s/%d took a split_lock trap at address: 0x%lx\n",
-			    current->comm, current->pid, regs->ip);
+			    current->comm, current->pid, ip);
 
 	/*
 	 * Disable the split lock detection for this task so it can make
@@ -1081,6 +1079,31 @@ bool handle_user_split_lock(struct pt_regs *regs, long error_code)
 	 */
 	sld_update_msr(false);
 	set_tsk_thread_flag(current, TIF_SLD);
+}
+
+bool handle_guest_split_lock(unsigned long ip)
+{
+	if (sld_state == sld_warn) {
+		split_lock_warn(ip);
+		return true;
+	}
+
+	pr_warn_once("#AC: %s/%d %s split_lock trap at address: 0x%lx\n",
+		     current->comm, current->pid,
+		     sld_state == sld_fatal ? "fatal" : "bogus", ip);
+
+	current->thread.error_code = 0;
+	current->thread.trap_nr = X86_TRAP_AC;
+	force_sig_fault(SIGBUS, BUS_ADRALN, NULL);
+	return false;
+}
+EXPORT_SYMBOL_GPL(handle_guest_split_lock);
+
+bool handle_user_split_lock(struct pt_regs *regs, long error_code)
+{
+	if ((regs->flags & X86_EFLAGS_AC) || sld_state == sld_fatal)
+		return false;
+	split_lock_warn(regs->ip);
 	return true;
 }