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From: "tip-bot2 for Borislav Petkov" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Sergei Trofimovich <slyfox@gentoo.org>,
	Borislav Petkov <bp@suse.de>, Kalle Valo <kvalo@codeaurora.org>,
	<stable@vger.kernel.org>, x86 <x86@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: [tip: x86/urgent] x86: Fix early boot crash on gcc-10, third try
Date: Fri, 15 May 2020 11:20:04 -0000
Message-ID: <158954160454.17951.15828011095215471629.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20200314164451.346497-1-slyfox@gentoo.org>

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

Commit-ID:     a9a3ed1eff3601b63aea4fb462d8b3b92c7c1e7e
Gitweb:        https://git.kernel.org/tip/a9a3ed1eff3601b63aea4fb462d8b3b92c7c1e7e
Author:        Borislav Petkov <bp@suse.de>
AuthorDate:    Wed, 22 Apr 2020 18:11:30 +02:00
Committer:     Borislav Petkov <bp@suse.de>
CommitterDate: Fri, 15 May 2020 11:48:01 +02:00

x86: Fix early boot crash on gcc-10, third try

... or the odyssey of trying to disable the stack protector for the
function which generates the stack canary value.

The whole story started with Sergei reporting a boot crash with a kernel
built with gcc-10:

  Kernel panic — not syncing: stack-protector: Kernel stack is corrupted in: start_secondary
  CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.6.0-rc5—00235—gfffb08b37df9 #139
  Hardware name: Gigabyte Technology Co., Ltd. To be filled by O.E.M./H77M—D3H, BIOS F12 11/14/2013
  Call Trace:
    dump_stack
    panic
    ? start_secondary
    __stack_chk_fail
    start_secondary
    secondary_startup_64
  -—-[ end Kernel panic — not syncing: stack—protector: Kernel stack is corrupted in: start_secondary

This happens because gcc-10 tail-call optimizes the last function call
in start_secondary() - cpu_startup_entry() - and thus emits a stack
canary check which fails because the canary value changes after the
boot_init_stack_canary() call.

To fix that, the initial attempt was to mark the one function which
generates the stack canary with:

  __attribute__((optimize("-fno-stack-protector"))) ... start_secondary(void *unused)

however, using the optimize attribute doesn't work cumulatively
as the attribute does not add to but rather replaces previously
supplied optimization options - roughly all -fxxx options.

The key one among them being -fno-omit-frame-pointer and thus leading to
not present frame pointer - frame pointer which the kernel needs.

The next attempt to prevent compilers from tail-call optimizing
the last function call cpu_startup_entry(), shy of carving out
start_secondary() into a separate compilation unit and building it with
-fno-stack-protector, was to add an empty asm("").

This current solution was short and sweet, and reportedly, is supported
by both compilers but we didn't get very far this time: future (LTO?)
optimization passes could potentially eliminate this, which leads us
to the third attempt: having an actual memory barrier there which the
compiler cannot ignore or move around etc.

That should hold for a long time, but hey we said that about the other
two solutions too so...

Reported-by: Sergei Trofimovich <slyfox@gentoo.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Kalle Valo <kvalo@codeaurora.org>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20200314164451.346497-1-slyfox@gentoo.org
---
 arch/x86/include/asm/stackprotector.h | 7 ++++++-
 arch/x86/kernel/smpboot.c             | 8 ++++++++
 arch/x86/xen/smp_pv.c                 | 1 +
 include/linux/compiler.h              | 6 ++++++
 init/main.c                           | 2 ++
 5 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
index 91e29b6..9804a79 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 8c89e4d..2f24c33 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -266,6 +266,14 @@ 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 8fb8a50..f2adb63 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -93,6 +93,7 @@ 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 034b0a6..448c91b 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()	mb()
+
 #endif /* __LINUX_COMPILER_H */
diff --git a/init/main.c b/init/main.c
index 1a5da2c..ad3812b 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1036,6 +1036,8 @@ asmlinkage __visible void __init start_kernel(void)
 
 	/* Do the rest non-__init'ed, we're now alive */
 	arch_call_rest_init();
+
+	prevent_tail_call_optimization();
 }
 
 /* Call all constructor functions linked into the kernel. */

      parent reply index

Thread overview: 79+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-14 16:44 [PATCH] x86: fix early boot crash on gcc-10 Sergei Trofimovich
2020-03-16 13:04 ` Peter Zijlstra
2020-03-16 13:26   ` Jakub Jelinek
2020-03-16 13:42     ` Peter Zijlstra
2020-03-16 17:54       ` Borislav Petkov
2020-03-16 18:03         ` Jakub Jelinek
2020-03-17 14:36           ` Borislav Petkov
2020-03-17 14:39             ` Jakub Jelinek
2020-03-17 14:49               ` Borislav Petkov
2020-03-17 16:35                 ` David Laight
2020-03-25 13:31                 ` Borislav Petkov
2020-03-26 21:54                   ` Sergei Trofimovich
2020-03-26 22:35                     ` Borislav Petkov
2020-03-28  8:48                       ` [PATCH v2] " Sergei Trofimovich
2020-04-13 14:15                         ` [tip: x86/urgent] x86: Fix " tip-bot2 for Sergei Trofimovich
2020-04-13 16:35                         ` [PATCH v2] x86: fix " Borislav Petkov
2020-04-14 13:50                           ` Michael Matz
2020-04-15  7:48                             ` Borislav Petkov
2020-04-15 14:53                               ` Michael Matz
2020-04-15 22:19                                 ` Sergei Trofimovich
2020-04-17  7:57                                   ` Borislav Petkov
2020-04-17  8:07                                     ` Jakub Jelinek
2020-04-17  8:42                                       ` Borislav Petkov
2020-04-17  8:58                                         ` Jakub Jelinek
2020-04-17  9:09                                           ` Borislav Petkov
2020-04-17 18:15                                             ` Nick Desaulniers
2020-04-17 18:22                                               ` Nick Desaulniers
2020-04-17 19:06                                                 ` Jakub Jelinek
2020-04-17 19:49                                                   ` Nick Desaulniers
2020-04-17 19:53                                                     ` Nick Desaulniers
2020-04-20 14:04                                                     ` Michael Matz
2020-04-22 10:23                                                       ` Borislav Petkov
2020-04-22 11:40                                                         ` Peter Zijlstra
2020-04-22 13:49                                                           ` Borislav Petkov
2020-04-22 13:55                                                             ` Jakub Jelinek
2020-04-22 14:16                                                               ` Martin Liška
2020-04-22 15:06                                                                 ` Michael Matz
2020-04-22 16:53                                                                 ` Borislav Petkov
2020-04-22 17:02                                                                   ` Jakub Jelinek
2020-04-22 18:47                                                                   ` Nick Desaulniers
2020-04-22 18:55                                                         ` Nick Desaulniers
2020-04-22 19:21                                                           ` Borislav Petkov
2020-04-22 21:05                                                             ` Nick Desaulniers
2020-04-22 21:26                                                               ` Borislav Petkov
2020-04-22 22:57                                                                 ` Nick Desaulniers
2020-04-23 12:53                                                                   ` Borislav Petkov
2020-04-23 16:12                                                                     ` [PATCH] x86: Fix early boot crash on gcc-10, next try Borislav Petkov
2020-04-23 17:30                                                                       ` Borislav Petkov
2020-04-23 18:02                                                                         ` Nick Desaulniers
2020-04-23 18:27                                                                           ` Borislav Petkov
2020-04-27 11:37                                                                         ` [tip: x86/build] x86/build: Check whether the compiler is sane tip-bot2 for Borislav Petkov
2020-04-23 19:40                                                                       ` [PATCH] x86: Fix early boot crash on gcc-10, next try Kees Cook
2020-04-25  1:46                                                                       ` Arvind Sankar
2020-04-25  8:57                                                                         ` Borislav Petkov
2020-04-25 11:09                                                                           ` Jürgen Groß
2020-04-25 15:04                                                                           ` Arvind Sankar
2020-04-25 17:31                                                                             ` Borislav Petkov
2020-04-25 17:52                                                                               ` Borislav Petkov
2020-04-27 17:07                                                                                 ` David Laight
2020-04-25 18:37                                                                               ` Segher Boessenkool
2020-04-25 18:53                                                                                 ` Borislav Petkov
2020-04-25 19:15                                                                                   ` Segher Boessenkool
2020-04-25 22:17                                                                                     ` Borislav Petkov
2020-04-25 22:25                                                                                     ` Arvind Sankar
2020-04-17 10:38                                           ` [PATCH v2] x86: fix early boot crash on gcc-10 Peter Zijlstra
2020-04-18 13:12                                             ` David Laight
2020-04-17 10:41                                     ` Peter Zijlstra
2020-03-16 18:20         ` [PATCH] " Arvind Sankar
2020-03-16 18:54           ` Arvind Sankar
2020-03-16 19:53             ` Arvind Sankar
2020-03-16 20:08               ` Jakub Jelinek
2020-03-16 20:40                 ` Arvind Sankar
2020-03-16 22:12     ` Sergei Trofimovich
2020-03-17 11:46       ` Jakub Jelinek
2020-03-17 18:10         ` Sergei Trofimovich
2020-03-16 18:22 ` Arvind Sankar
2020-03-26 23:16 ` [PATCH v2] " Sergei Trofimovich
2020-04-27 11:37 ` [tip: x86/build] x86: Fix early boot crash on gcc-10, next try tip-bot2 for Borislav Petkov
2020-05-15 11:20 ` tip-bot2 for Borislav Petkov [this message]

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