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From: Kees Cook <keescook@chromium.org>
To: Borislav Petkov <bp@alien8.de>
Cc: "Nick Desaulniers" <ndesaulniers@google.com>,
	"Michael Matz" <matz@suse.de>, "Jakub Jelinek" <jakub@redhat.com>,
	"Sergei Trofimovich" <slyfox@gentoo.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Andy Lutomirski" <luto@kernel.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	x86@kernel.org,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	"Martin Liška" <mliska@suse.cz>
Subject: Re: [PATCH] x86: Fix early boot crash on gcc-10, next try
Date: Thu, 23 Apr 2020 12:40:35 -0700
Message-ID: <202004231237.AB249F90@keescook> (raw)
In-Reply-To: <20200423161126.GD26021@zn.tnic>

On Thu, Apr 23, 2020 at 06:12:24PM +0200, Borislav Petkov wrote:
> Ok,
> 
> I have tried to summarize our odyssey so far and here's what I came up
> with. Just built latest gcc from the git repo and it seems to work.
> 
> Next I need to come up with a slick way of testing the compiler...
> 
> Thx.
> 
> ---
> From: Borislav Petkov <bp@suse.de>
> 
> ... 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, is this one.
> 
> The current solution is short and sweet, and reportedly, is supported by
> both compilers so let's see how far we'll get this time.
> 
> Reported-by: Sergei Trofimovich <slyfox@gentoo.org>
> Signed-off-by: Borislav Petkov <bp@suse.de>

Reviewed-by: Kees Cook <keescook@chromium.org>

I'm glad to have the gcc bug opened for the function attribute; thanks
Nick! I needed that for the syscall entry code, but instead went with
a compilation-unit down-grade[1]. I'd much prefer the attribute. :)

-Kees

[1] https://lore.kernel.org/lkml/20200406231606.37619-5-keescook@chromium.org/

> Link: https://lkml.kernel.org/r/20200314164451.346497-1-slyfox@gentoo.org
> ---
>  arch/x86/kernel/smpboot.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 3b9bf8c7e29d..e9f44727fccd 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 functions up, in
> +	 * boot_init_stack_canary() and must not be checked before tail calling
> +	 * another function.
> +	 */
> +	asm ("");
>  }
>  
>  /**
> -- 
> 2.21.0
> 
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette

-- 
Kees Cook

  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                                                                       ` Kees Cook [this message]
2020-04-25  1:46                                                                       ` [PATCH] x86: Fix early boot crash on gcc-10, next try 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: x86/urgent] x86: Fix early boot crash on gcc-10, third try tip-bot2 for Borislav Petkov

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