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Subject: Re: [RFC v2 PATCH 7/7] x86/entry: use int for syscall number; handle
 all invalid syscall nrs
To:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <871racf928.ffs@nanos.tec.linutronix.de>
From:   "H. Peter Anvin" <hpa@zytor.com>
Message-ID: <60495dd3-ea68-4db3-47ad-b7b45796bf76@zytor.com>
Date:   Wed, 12 May 2021 11:21:38 -0700
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On 5/12/21 5:09 AM, Thomas Gleixner wrote:
> 
>> index 1d9db15fdc69..85f04ea0e368 100644
>> --- a/arch/x86/entry/entry_64.S
>> +++ b/arch/x86/entry/entry_64.S
>> @@ -108,7 +108,7 @@ SYM_INNER_LABEL(entry_SYSCALL_64_after_hwframe, SYM_L_GLOBAL)
>>   
>>   	/* IRQs are off. */
>>   	movq	%rsp, %rdi
>> -	movq	%rax, %rsi
>> +	movslq	%eax, %rsi
> 
> This is wrong.
> 
>    syscall(long number,...);
> 
> So the above turns syscall(UINT_MAX + N, ...) into syscall(N, ...).
> 

That is intentional, as (again) system calls are int. As stated in my 
reply to Ingo, I'll clean the various descriptions and try to capture 
the discussion better.

	-hpa