linux-kernel - Re: [PATCH] selftests: x86: add version check in test_syscall

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Message-ID: <20190302091047.GA14963@kroah.com>
Date:   Sat, 2 Mar 2019 10:10:47 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Steve Muckle <smuckle@...gle.com>, Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH] selftests: x86: add version check in test_syscall_vdso

On Fri, Mar 01, 2019 at 11:59:24AM -0800, Andy Lutomirski wrote:
> > On Feb 28, 2019, at 4:18 PM, Steve Muckle <smuckle@...gle.com> wrote:
> >
> > Since 4.17 registers r8-r11 are not clobbered/zeroed by a 64-bit kernel
> > handling a 32-bit syscall and this behavior is enforced by the
> > test_syscall_vdso testcase. See commit 8bb2610bc496
> > ("x86/entry/64/compat: Preserve r8-r11 in int $0x80").
> >
> > Permit the old behavior in the testcase for kernels prior to 4.17.
> 
> NAK.  If you want an old buggy kernel to pass a test, please either
> patch the kernel or run an old test.

Yeah, this isn't ok, especially as you might have 4.14 or 4.9 kernels
that can pass the test if the needed patches were backported.  Checking
kernel version numbers should never be used for anything.

greg k-h