x86/stackprotector: Pre-initialize canary for secondary CPUs

The idle tasks created for each secondary CPU already have a random stack
canary generated by fork().  Copy the canary to the percpu variable before
starting the secondary CPU which removes the need to call
boot_init_stack_canary().

Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200617225624.799335-1-brgerst@gmail.com

diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
index 9804a7957f4e99fa547923995562c415e451c573..7fb482f0f25b062c073294ef72fd6936bf36c41c 100644 (file)
--- a/arch/x86/include/asm/stackprotector.h
+++ b/arch/x86/include/asm/stackprotector.h
@@ -90,6 +90,15 @@ static __always_inline void boot_init_stack_canary(void)
 #endif
 }
 
+static inline void cpu_init_stack_canary(int cpu, struct task_struct *idle)
+{
+#ifdef CONFIG_X86_64
+       per_cpu(fixed_percpu_data.stack_canary, cpu) = idle->stack_canary;
+#else
+       per_cpu(stack_canary.canary, cpu) = idle->stack_canary;
+#endif
+}
+
 static inline void setup_stack_canary_segment(int cpu)
 {
 #ifdef CONFIG_X86_32
@@ -119,6 +128,9 @@ static inline void load_stack_canary_segment(void)
 static inline void setup_stack_canary_segment(int cpu)
 { }
 
+static inline void cpu_init_stack_canary(int cpu, struct task_struct *idle)
+{ }
+
 static inline void load_stack_canary_segment(void)
 {
 #ifdef CONFIG_X86_32

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index ffbd9a3d78d849c63c7b809e25b629aedf6e8806..a11bd53c691187820812ae3c7906af881578ea8e 100644 (file)
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -51,7 +51,6 @@
 #include <linux/err.h>
 #include <linux/nmi.h>
 #include <linux/tboot.h>
-#include <linux/stackprotector.h>
 #include <linux/gfp.h>
 #include <linux/cpuidle.h>
 #include <linux/numa.h>
@@ -80,6 +79,7 @@
 #include <asm/cpu_device_id.h>
 #include <asm/spec-ctrl.h>
 #include <asm/hw_irq.h>
+#include <asm/stackprotector.h>
 
 /* representing HT siblings of each logical CPU */
 DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_sibling_map);
@@ -259,21 +259,10 @@ static void notrace start_secondary(void *unused)
        /* enable local interrupts */
        local_irq_enable();
 
-       /* to prevent fake stack check failure in clock setup */
-       boot_init_stack_canary();
-
        x86_cpuinit.setup_percpu_clockev();
 
        wmb();
        cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
-
-       /*
-        * Prevent tail call to cpu_startup_entry() because the stack protector
-        * guard has been changed a couple of function calls up, in
-        * boot_init_stack_canary() and must not be checked before tail calling
-        * another function.
-        */
-       prevent_tail_call_optimization();
 }
 
 /**
@@ -1011,6 +1000,7 @@ int common_cpu_up(unsigned int cpu, struct task_struct *idle)
        alternatives_enable_smp();
 
        per_cpu(current_task, cpu) = idle;
+       cpu_init_stack_canary(cpu, idle);
 
        /* Initialize the interrupt stack(s) */
        ret = irq_init_percpu_irqstack(cpu);

diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index 171aff1b11f24e38923b529a060d88f60247225b..9ea598dcc132fc4c7ef02cd23f918892082d65b6 100644 (file)
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -92,9 +92,7 @@ static void cpu_bringup(void)
 asmlinkage __visible void cpu_bringup_and_idle(void)
 {
        cpu_bringup();
-       boot_init_stack_canary();
        cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
-       prevent_tail_call_optimization();
 }
 
 void xen_smp_intr_free_pv(unsigned int cpu)