linux-kernel - Re: [RFC PATCH v2 1/2] selftests/x86: sysret

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Message-ID: <ea9dbc3c-0148-ecf1-d68f-2fcd1d026c36@zytor.com>
Date:   Mon, 23 Jan 2023 21:44:59 -0800
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>,
        x86 Mailing List <x86@...nel.org>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xin Li <xin3.li@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Brian Gerst <brgerst@...il.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Shuah Khan <shuah@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linux Kselftest Mailing List 
        <linux-kselftest@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 1/2] selftests/x86: sysret_rip: Handle syscall in a
 FRED system



On 1/23/23 18:27, Ammar Faizi wrote:
> From: Ammar Faizi <ammarfaizi2@...weeb.org>
> 
> The current selftest asserts %r11 == %rflags after the 'syscall'
> returns to user. Such an assertion doesn't apply to a FRED system
> because in a FRED system the 'syscall' instruction does not set
> %r11=%rflags and %rcx=%rip.
> 
> Handle the FRED case. Now, test that:
> 
>    - "syscall" in a FRED system doesn't clobber %rcx and %r11.
>    - "syscall" in a non-FRED system sets %rcx=%rip and %r11=%rflags.
> 
> The 'raise()' function from libc can't be used to control those
> registers. Therefore, create a syscall wrapper in inline Assembly to
> fully control them.
> 
> Fixes: 660602140103 ("selftests/x86: Add a selftest for SYSRET to noncanonical addresses")
> Link: https://lore.kernel.org/lkml/25b96960-a07e-a952-5c23-786b55054126@zytor.com
> Reported-by: Xin Li <xin3.li@...el.com>
> Co-developed-by: "H. Peter Anvin" <hpa@...or.com>
> Signed-off-by: Ammar Faizi <ammarfaizi2@...weeb.org>
> ---
> 
> Need hpa's sign off.
> 

For both patches:

Acked-by: H. Peter Anvin (Intel) <hpa@...or.com>