linux-kernel - Re: [PATCH 1/4] x86: add __X32_COND

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Message-ID: <20200919053514.GI30063@infradead.org>
Date:   Sat, 19 Sep 2020 06:35:14 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Eric Biederman <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        kexec@...ts.infradead.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Christoph Hellwig <hch@....de>, Arnd Bergmann <arnd@...db.de>,
        Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH 1/4] x86: add __X32_COND_SYSCALL() macro

On Fri, Sep 18, 2020 at 03:24:36PM +0200, Arnd Bergmann wrote:
> sys_move_pages() is an optional syscall, and once we remove
> the compat version of it in favor of the native one with an
> in_compat_syscall() check, the x32 syscall table refers to
> a __x32_sys_move_pages symbol that may not exist when the
> syscall is disabled.
> 
> Change the COND_SYSCALL() definition on x86 to also include
> the redirection for x32.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Adding the x86 maintainers and Brian Gerst.  Brian proposed another
problem to the mess that most of the compat syscall handlers used by
x32 here:

   https://lkml.org/lkml/2020/6/16/664

hpa didn't particularly like it, but with your and my pending series
we'll soon use more native than compat syscalls for x32, so something
will need to change..

> ---
>  arch/x86/include/asm/syscall_wrapper.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/include/asm/syscall_wrapper.h b/arch/x86/include/asm/syscall_wrapper.h
> index a84333adeef2..5eacd35a7f97 100644
> --- a/arch/x86/include/asm/syscall_wrapper.h
> +++ b/arch/x86/include/asm/syscall_wrapper.h
> @@ -171,12 +171,16 @@ extern long __ia32_sys_ni_syscall(const struct pt_regs *regs);
>  	__SYS_STUBx(x32, compat_sys##name,				\
>  		    SC_X86_64_REGS_TO_ARGS(x, __VA_ARGS__))
>  
> +#define __X32_COND_SYSCALL(name)					\
> +	__COND_SYSCALL(x32, sys_##name)
> +
>  #define __X32_COMPAT_COND_SYSCALL(name)					\
>  	__COND_SYSCALL(x32, compat_sys_##name)
>  
>  #define __X32_COMPAT_SYS_NI(name)					\
>  	__SYS_NI(x32, compat_sys_##name)
>  #else /* CONFIG_X86_X32 */
> +#define __X32_COND_SYSCALL(name)
>  #define __X32_COMPAT_SYS_STUB0(name)
>  #define __X32_COMPAT_SYS_STUBx(x, name, ...)
>  #define __X32_COMPAT_COND_SYSCALL(name)
> @@ -253,6 +257,7 @@ extern long __ia32_sys_ni_syscall(const struct pt_regs *regs);
>  	static long __do_sys_##sname(const struct pt_regs *__unused)
>  
>  #define COND_SYSCALL(name)						\
> +	__X32_COND_SYSCALL(name)					\
>  	__X64_COND_SYSCALL(name)					\
>  	__IA32_COND_SYSCALL(name)
>  
> -- 
> 2.27.0
> 
---end quoted text---