linux-kernel - Re: [PATCH RFC 16/43] x86-64: Use per-cpu stack canary if supported by compiler

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Date:   Thu, 4 May 2023 12:31:59 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Hou Wenlong <houwenlong.hwl@...group.com>,
        linux-kernel@...r.kernel.org
Cc:     Thomas Garnier <thgarnie@...omium.org>,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Kees Cook <keescook@...omium.org>,
        Brian Gerst <brgerst@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Mike Rapoport (IBM)" <rppt@...nel.org>,
        Ashok Raj <ashok.raj@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Guo Ren <guoren@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Kim Phillips <kim.phillips@....com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        xen-devel@...ts.xenproject.org,
        platform-driver-x86@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH RFC 16/43] x86-64: Use per-cpu stack canary if supported
 by compiler

On 28.04.23 11:50, Hou Wenlong wrote:
> From: Brian Gerst <brgerst@...il.com>
> 
> From: Brian Gerst <brgerst@...il.com>
> 
> If the compiler supports it, use a standard per-cpu variable for the
> stack protector instead of the old fixed location.  Keep the fixed
> location code for compatibility with older compilers.
> 
> [Hou Wenlong: Disable it on Clang, adapt new code change and adapt
> missing GS set up path in pvh_start_xen()]
> 
> Signed-off-by: Brian Gerst <brgerst@...il.com>
> Co-developed-by: Hou Wenlong <houwenlong.hwl@...group.com>
> Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
> Cc: Thomas Garnier <thgarnie@...omium.org>
> Cc: Lai Jiangshan <jiangshan.ljs@...group.com>
> Cc: Kees Cook <keescook@...omium.org>
> ---
>   arch/x86/Kconfig                      | 12 ++++++++++++
>   arch/x86/Makefile                     | 21 ++++++++++++++-------
>   arch/x86/entry/entry_64.S             |  6 +++++-
>   arch/x86/include/asm/processor.h      | 17 ++++++++++++-----
>   arch/x86/include/asm/stackprotector.h | 16 +++++++---------
>   arch/x86/kernel/asm-offsets_64.c      |  2 +-
>   arch/x86/kernel/cpu/common.c          | 15 +++++++--------
>   arch/x86/kernel/head_64.S             | 16 ++++++++++------
>   arch/x86/kernel/vmlinux.lds.S         |  4 +++-
>   arch/x86/platform/pvh/head.S          |  8 ++++++++
>   arch/x86/xen/xen-head.S               | 14 +++++++++-----
>   11 files changed, 88 insertions(+), 43 deletions(-)
> 

...

> diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
> index 643d02900fbb..09eaf59e8066 100644
> --- a/arch/x86/xen/xen-head.S
> +++ b/arch/x86/xen/xen-head.S
> @@ -51,15 +51,19 @@ SYM_CODE_START(startup_xen)
>   
>   	leaq	(__end_init_task - PTREGS_SIZE)(%rip), %rsp
>   
> -	/* Set up %gs.
> -	 *
> -	 * The base of %gs always points to fixed_percpu_data.  If the
> -	 * stack protector canary is enabled, it is located at %gs:40.
> +	/*
> +	 * Set up GS base.
>   	 * Note that, on SMP, the boot cpu uses init data section until
>   	 * the per cpu areas are set up.
>   	 */
>   	movl	$MSR_GS_BASE,%ecx
> -	movq	$INIT_PER_CPU_VAR(fixed_percpu_data),%rax
> +#if defined(CONFIG_STACKPROTECTOR_FIXED)
> +	leaq	INIT_PER_CPU_VAR(fixed_percpu_data)(%rip), %rdx
> +#elif defined(CONFIG_SMP)
> +	movabs	$__per_cpu_load, %rdx

Shouldn't above 2 targets be %rax?

> +#else
> +	xorl	%eax, %eax
> +#endif
>   	cdq
>   	wrmsr
>   


Juergen

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