1 files changed, 65 insertions, 0 deletions
diff --git a/stackcanary.patch b/stackcanary.patch
new file mode 100644
index 000000000000..50e58c8cb371
--- /dev/null
+++ b/stackcanary.patch
@@ -0,0 +1,65 @@
+diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
+index 91e29b6a86a5..9804a7957f4e 100644
+--- a/arch/x86/include/asm/stackprotector.h
++++ b/arch/x86/include/asm/stackprotector.h
+@@ -55,8 +55,13 @@
+ /*
+  * Initialize the stackprotector canary value.
+  *
+- * NOTE: this must only be called from functions that never return,
++ * NOTE: this must only be called from functions that never return
+  * and it must always be inlined.
++ *
++ * In addition, it should be called from a compilation unit for which
++ * stack protector is disabled. Alternatively, the caller should not end
++ * with a function call which gets tail-call optimized as that would
++ * lead to checking a modified canary value.
+  */
+ static __always_inline void boot_init_stack_canary(void)
+ {
+diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
+index 69881b2d446c..9674321ce3a3 100644
+--- a/arch/x86/kernel/smpboot.c
++++ b/arch/x86/kernel/smpboot.c
+@@ -262,6 +262,14 @@ static void notrace start_secondary(void *unused)
+ 
+ 	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();
+ }
+ 
+ /**
+diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
+index 802ee5bba66c..0cebe5db691d 100644
+--- a/arch/x86/xen/smp_pv.c
++++ b/arch/x86/xen/smp_pv.c
+@@ -92,6 +92,7 @@ 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)
+diff --git a/include/linux/compiler.h b/include/linux/compiler.h
+index 034b0a644efc..732754d96039 100644
+--- a/include/linux/compiler.h
++++ b/include/linux/compiler.h
+@@ -356,4 +356,10 @@ static inline void *offset_to_ptr(const int *off)
+ /* &a[0] degrades to a pointer: a different type from an array */
+ #define __must_be_array(a)	BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
+ 
++/*
++ * This is needed in functions which generate the stack canary, see
++ * arch/x86/kernel/smpboot.c::start_secondary() for an example.
++ */
++#define prevent_tail_call_optimization()	asm("")
++
+ #endif /* __LINUX_COMPILER_H */