Commit 5e408396 authored by Sean Christopherson's avatar Sean Christopherson
Browse files

x86/reboot: Harden virtualization hooks for emergency reboot 



Provide dedicated helpers to (un)register virt hooks used during an
emergency crash/reboot, and WARN if there is an attempt to overwrite
the registered callback, or an attempt to do an unpaired unregister.

Opportunsitically use rcu_assign_pointer() instead of RCU_INIT_POINTER(),
mainly so that the set/unset paths are more symmetrical, but also because
any performance gains from using RCU_INIT_POINTER() are meaningless for
this code.

Reviewed-by: default avatarKai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20230721201859.2307736-3-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent b23c83ad

arch/x86/include/asm/reboot.h

+3 −2
Original line number Diff line number Diff line
@@ -25,8 +25,9 @@ void __noreturn machine_real_restart(unsigned int type); 
#define MRR_BIOS	0

#define MRR_APM		1



typedef void crash_vmclear_fn(void);

extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss;

typedef void (cpu_emergency_virt_cb)(void);

void cpu_emergency_register_virt_callback(cpu_emergency_virt_cb *callback);

void cpu_emergency_unregister_virt_callback(cpu_emergency_virt_cb *callback);

void cpu_emergency_disable_virtualization(void);



typedef void (*nmi_shootdown_cb)(int, struct pt_regs*);

arch/x86/kernel/reboot.c

+24 −6
Original line number Diff line number Diff line
@@ -794,17 +794,35 @@ void machine_crash_shutdown(struct pt_regs *regs) 
 *

 * protected by rcu.

 */

crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss;

EXPORT_SYMBOL_GPL(crash_vmclear_loaded_vmcss);

static cpu_emergency_virt_cb __rcu *cpu_emergency_virt_callback;



void cpu_emergency_register_virt_callback(cpu_emergency_virt_cb *callback)

{

	if (WARN_ON_ONCE(rcu_access_pointer(cpu_emergency_virt_callback)))

		return;



	rcu_assign_pointer(cpu_emergency_virt_callback, callback);

}

EXPORT_SYMBOL_GPL(cpu_emergency_register_virt_callback);



void cpu_emergency_unregister_virt_callback(cpu_emergency_virt_cb *callback)

{

	if (WARN_ON_ONCE(rcu_access_pointer(cpu_emergency_virt_callback) != callback))

		return;



	rcu_assign_pointer(cpu_emergency_virt_callback, NULL);

	synchronize_rcu();

}

EXPORT_SYMBOL_GPL(cpu_emergency_unregister_virt_callback);



static inline void cpu_crash_vmclear_loaded_vmcss(void)

{

	crash_vmclear_fn *do_vmclear_operation = NULL;

	cpu_emergency_virt_cb *callback;



	rcu_read_lock();

	do_vmclear_operation = rcu_dereference(crash_vmclear_loaded_vmcss);

	if (do_vmclear_operation)

		do_vmclear_operation();

	callback = rcu_dereference(cpu_emergency_virt_callback);

	if (callback)

		callback();

	rcu_read_unlock();

}

arch/x86/kvm/vmx/vmx.c

+2 −4
Original line number Diff line number Diff line
@@ -8571,8 +8571,7 @@ static void __vmx_exit(void) 
{

	allow_smaller_maxphyaddr = false;



	RCU_INIT_POINTER(crash_vmclear_loaded_vmcss, NULL);

	synchronize_rcu();

	cpu_emergency_unregister_virt_callback(crash_vmclear_local_loaded_vmcss);



	vmx_cleanup_l1d_flush();

}
@@ -8620,8 +8619,7 @@ static int __init vmx_init(void) 
		pi_init_cpu(cpu);

	}



	rcu_assign_pointer(crash_vmclear_loaded_vmcss,

			   crash_vmclear_local_loaded_vmcss);

	cpu_emergency_register_virt_callback(crash_vmclear_local_loaded_vmcss);



	vmx_check_vmcs12_offsets();