linux-kernel - [PATCH] idle/x86: remove the call to boot_init_stack_canary() from cpu_startup

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Message-Id: <f1b058d6a73cfb68b36dc755df5aaa7a064875b1.1539935852.git.christophe.leroy@c-s.fr>
Date:   Fri, 19 Oct 2018 09:29:22 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] idle/x86: remove the call to boot_init_stack_canary() from
 cpu_startup_entry()

commit d7880812b359 ("idle: Add the stack canary init to
cpu_startup_entry()") added the call to boot_init_stack_canary()
in cpu_startup_entry() in an #ifdef CONFIG_X86 statement, with
the intention to remove that #ifdef later.

While implementing stack protector for powerpc, it has been
observed 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 arches
using global stack canary (ARM, SH, MIPS and XTENSA).

Instead of adding modifying the #ifdef in a
implemented the call to boot_init_stack_canary() in the function
calling cpu_startup_entry()

On x86, we have two functions calling cpu_startup_entry():
- start_secondary()
- cpu_bringup_and_idle()

start_secondary() already calls boot_init_stack_canary().

This patch adds the call to boot_init_stack_canary() in
cpu_bringup_and_idle() and removes it from cpu_startup_entry()

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 arch/x86/xen/smp_pv.c |  1 +
 kernel/sched/idle.c   | 15 ---------------
 2 files changed, 1 insertion(+), 15 deletions(-)

diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index e3b18ad49889..0e05e8e23998 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -88,6 +88,7 @@ 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)
-- 
2.13.3