Message-ID: <8d66a0ff-54b5-ab0a-2638-6f11c1c0d6f5@gnuweeb.org>
Date:   Wed, 25 Jan 2023 17:01:27 +0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.4.2
Subject: Re: [RFC PATCH v5 1/2] selftests/x86: sysret_rip: Handle syscall in a
 FRED system
Content-Language: en-US
From:   Ammar Faizi <ammarfaizi2@gnuweeb.org>
To:     "H. Peter Anvin" <hpa@zytor.com>
Cc:     Xin Li <xin3.li@intel.com>, Dave Hansen <dave.hansen@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Cooper <Andrew.Cooper3@citrix.com>,
        Brian Gerst <brgerst@gmail.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Shuah Khan <shuah@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        x86 Mailing List <x86@kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Linux Kselftest Mailing List 
        <linux-kselftest@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <5ecc383c-621b-57d9-7f6d-d63496fca3b3@zytor.com>
 <20230124022729.596997-1-ammarfaizi2@gnuweeb.org>
 <20230124022729.596997-3-ammarfaizi2@gnuweeb.org>
 <ce25e53f-91d4-d793-42a5-036d6bce0b4c@zytor.com>
 <Y899kHYbz32H1S6a@biznet-home.integral.gnuweeb.org>
 <BC632CA8-D2CB-4781-82E5-9810347293B0@zytor.com>
 <Y8+hGxVpgFVcm15g@biznet-home.integral.gnuweeb.org>
 <20230125034958.734527-1-ammarfaizi2@gnuweeb.org>
 <20230125034958.734527-2-ammarfaizi2@gnuweeb.org>
 <8770815f-0f23-d0c5-e56a-d401827842c9@zytor.com>
 <Y9D8++DxphJS1oc4@biznet-home.integral.gnuweeb.org>
In-Reply-To: <Y9D8++DxphJS1oc4@biznet-home.integral.gnuweeb.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 1/25/23 4:57 PM, Ammar Faizi wrote:
> On Wed, Jan 25, 2023 at 12:39:26AM -0800, H. Peter Anvin wrote:
>>>    	/* Set IP and CX to match so that SYSRET can happen. */
>>>    	ctx->uc_mcontext.gregs[REG_RIP] = rip;
>>>    	ctx->uc_mcontext.gregs[REG_RCX] = rip;
>>
>> It would be interesting to have the syscall handler try both with and
>> without this (so it would end up doing both IRET and SYSCALL on legacy.)
>> Perhaps SIGUSR1 versus SIGUSR2...
> 
> Just to clarify this more so I am sure I understand it correctly.
> 
> Did you mean to have the same signal handler without modifiying
> 'REG_RCX' but still change 'REG_RIP'?
> 
> IOW, we want to only *remove*:
> 
>     ctx->uc_mcontext.gregs[REG_RCX] = rip;
> 
> and *keep*:
> 
>     ctx->uc_mcontext.gregs[REG_RIP] = rip;
> 
> for the SIGUSR2 handler. Thus, inside the entry64 we will jump to the
> iret path because %rcx != %r11 upon rt_sigreturn()?

s/%rcx != %r11/%rcx != %rip/

-- 
Ammar Faizi