x86/stackprotector: Remove the call to boot_init_stack_canary() from cpu_startup_entry()

The following commit:

  d7880812b359 ("idle: Add the stack canary init to cpu_startup_entry()")

... added an x86 specific boot_init_stack_canary() call to the generic
cpu_startup_entry() as a temporary hack, with the intention to remove
the #ifdef CONFIG_X86 later.

More than 5 years later let's finally realize that plan! :-)

While implementing stack protector support for PowerPC, we found
that calling boot_init_stack_canary() is also needed for PowerPC
which uses per task (TLS) stack canary like the X86.

However, calling boot_init_stack_canary() would break architectures
using a global stack canary (ARM, SH, MIPS and XTENSA).

Instead of modifying the #ifdef CONFIG_X86 to an even messier:

   #if defined(CONFIG_X86) || defined(CONFIG_PPC)

PowerPC implemented the call to boot_init_stack_canary() in the function
calling cpu_startup_entry().

Let's try the same cleanup on the x86 side as well.

On x86 we have two functions calling cpu_startup_entry():

 - start_secondary()
 - cpu_bringup_and_idle()

start_secondary() already calls boot_init_stack_canary(), so
it's good, and this patch adds the call to boot_init_stack_canary()
in cpu_bringup_and_idle().

I.e. now x86 catches up to the rest of the world and the ugly init
sequence in init/main.c can be removed from cpu_startup_entry().

As a final benefit we can also remove the <linux/stackprotector.h>
dependency from <linux/sched.h>.

[ mingo: Improved the changelog a bit, added language explaining x86 borkage and sched.h change. ]
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/20181020072649.5B59310483E@pc16082vm.idsi0.si.c-s.fr
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index e3b18ad49889..145506f9fdbe 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -22,6 +22,7 @@
 #include <linux/tick.h>
 #include <linux/nmi.h>
 #include <linux/cpuhotplug.h>
+#include <linux/stackprotector.h>
 
 #include <asm/paravirt.h>
 #include <asm/desc.h>
@@ -88,6 +89,7 @@ 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);
 }