[tip: x86/urgent] x86: Fix early boot crash on gcc-10

[tip-bot2 for Sergei Trofimovich]

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     5871c72d659e5c312b9ad635034cab59f7786a98
Gitweb:        https://git.kernel.org/tip/5871c72d659e5c312b9ad635034cab59f7786a98
Author:        Sergei Trofimovich <slyfox@xxxxxxxxxx>
AuthorDate:    Sat, 28 Mar 2020 08:48:58 
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Mon, 13 Apr 2020 16:07:35 +02:00

x86: Fix early boot crash on gcc-10

Fix a boot failure where the kernel is built with gcc-10 with stack
protector enabled by default:

  Kernel panic â not syncing: stack-protector: Kernel stack is corrupted in: start_secondary
  CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.6.0-rc5â00235âgfffb08b37df9 #139
  Hardware name: Gigabyte Technology Co., Ltd. To be filled by O.E.M./H77MâD3H, BIOS F12 11/14/2013
  Call Trace:
    dump_stack
    panic
    ? start_secondary
    __stack_chk_fail
    start_secondary
    secondary_startup_64
  -â-[ end Kernel panic â not syncing: stackâprotector: Kernel stack is corrupted in: start_secondary

This happens because start_secondary() is responsible for setting
up initial stack canary value in smpboot.c but nothing prevents gcc
from inserting stack canary into start_secondary() itself before the
boot_init_stack_canary() call which sets up said canary value.

Inhibit the stack canary addition for start_secondary() only.

 [ bp: Massage a bit. ]

Signed-off-by: Sergei Trofimovich <slyfox@xxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: Jakub Jelinek <jakub@xxxxxxxxxx>
Cc: Michael Matz <matz@xxxxxxx>
Link: https://lkml.kernel.org/r/20200328084858.421444-1-slyfox@xxxxxxxxxx
---
 arch/x86/kernel/smpboot.c      | 6 +++++-
 include/linux/compiler-gcc.h   | 1 +
 include/linux/compiler_types.h | 4 ++++
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index fe3ab96..9ea28e5 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -209,10 +209,14 @@ static void smp_callin(void)
 
 static int cpu0_logical_apicid;
 static int enable_start_cpu0;
+
 /*
  * Activate a secondary processor.
+ *
+ * Note: boot_init_stack_canary() sets up the canary value so omit the stack
+ * canary creation for this function only.
  */
-static void notrace start_secondary(void *unused)
+static void __no_stack_protector notrace start_secondary(void *unused)
 {
 	/*
 	 * Don't put *anything* except direct CPU state initialization
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index d7ee4c6..fb67c74 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -172,3 +172,4 @@
 #endif
 
 #define __no_fgcse __attribute__((optimize("-fno-gcse")))
+#define __no_stack_protector __attribute__((optimize("-fno-stack-protector")))
diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index e970f97..069c981 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -203,6 +203,10 @@ struct ftrace_likely_data {
 #define asm_inline asm
 #endif
 
+#ifndef __no_stack_protector
+# define __no_stack_protector
+#endif
+
 #ifndef __no_fgcse
 # define __no_fgcse
 #endif