Commit d7e94dbd authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Borislav Petkov
Browse files

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: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Acked-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Link: https://lkml.kernel.org/r/20200410115516.978037132@linutronix.de
Link: https://lkml.kernel.org/r/20200402123258.895628824@linutronix.de
parent 5b8b9d0c

arch/x86/include/asm/cpu.h

+6 −0
Original line number Diff line number Diff line
@@ -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 */

arch/x86/kernel/cpu/intel.c

+28 −5
Original line number Diff line number Diff line
@@ -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;

}

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