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 <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lkml.kernel.org/r/20200410115516.978037132@linutronix.de
Link: https://lkml.kernel.org/r/20200402123258.895628824@linutronix.de

diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index ff6f3ca..dd17c2d 100644 (file)
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -44,6 +44,7 @@ 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) {}
@@ -51,5 +52,10 @@ 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
index 9a26e97..bf08d45 100644 (file)
--- 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;
 }