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Date:   Sun, 21 Oct 2018 22:03:49 -0700
From:   tip-bot for Christophe Leroy <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, jgross@...e.com,
        boris.ostrovsky@...cle.com, mingo@...nel.org, peterz@...radead.org,
        christophe.leroy@....fr, tglx@...utronix.de,
        torvalds@...ux-foundation.org, hpa@...or.com, bp@...en8.de
Subject: [tip:x86/mm] x86/stackprotector: Remove the call to
 boot_init_stack_canary() from cpu_startup_entry()

Commit-ID:  977e4be5eb714c48a67afc26a6c477f24130a1f2
Gitweb:     https://git.kernel.org/tip/977e4be5eb714c48a67afc26a6c477f24130a1f2
Author:     Christophe Leroy <christophe.leroy@....fr>
AuthorDate: Sat, 20 Oct 2018 09:26:49 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 22 Oct 2018 04:07:24 +0200

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@....fr>
Reviewed-by: Juergen Gross <jgross@...e.com>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linuxppc-dev@...ts.ozlabs.org
Cc: xen-devel@...ts.xenproject.org
Link: http://lkml.kernel.org/r/20181020072649.5B59310483E@pc16082vm.idsi0.si.c-s.fr
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/xen/smp_pv.c |  2 ++
 kernel/sched/idle.c   | 15 ---------------
 kernel/sched/sched.h  |  1 -
 3 files changed, 2 insertions(+), 16 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);
 }
 
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 16f84142f2f4..f5516bae0c1b 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -347,21 +347,6 @@ EXPORT_SYMBOL_GPL(play_idle);
 
 void cpu_startup_entry(enum cpuhp_state state)
 {
-	/*
-	 * This #ifdef needs to die, but it's too late in the cycle to
-	 * make this generic (ARM and SH have never invoked the canary
-	 * init for the non boot CPUs!). Will be fixed in 3.11
-	 */
-#ifdef CONFIG_X86
-	/*
-	 * If we're the non-boot CPU, nothing set the stack canary up
-	 * for us. The boot CPU already has it initialized but no harm
-	 * in doing it again. This is a good place for updating it, as
-	 * we wont ever return from this function (so the invalid
-	 * canaries already on the stack wont ever trigger).
-	 */
-	boot_init_stack_canary();
-#endif
 	arch_cpu_idle_prepare();
 	cpuhp_online_idle(state);
 	while (1)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 4a2e8cae63c4..5b00a816a4b3 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -56,7 +56,6 @@
 #include <linux/profile.h>
 #include <linux/rcupdate_wait.h>
 #include <linux/security.h>
-#include <linux/stackprotector.h>
 #include <linux/stop_machine.h>
 #include <linux/suspend.h>
 #include <linux/swait.h>

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