linux-kernel - Re: [PATCH v9 25/29] x86/umip: Force a page fault when unable to copy emulated result to user

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Message-ID: <20171027214658.GA14203@voyager>
Date:   Fri, 27 Oct 2017 14:46:58 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brian Gerst <brgerst@...il.com>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Liang Z Li <liang.z.li@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Huang Rui <ray.huang@....com>, Jiri Slaby <jslaby@...e.cz>,
        Jonathan Corbet <corbet@....net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Chen Yucong <slaoub@...il.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Shuah Khan <shuah@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        X86 ML <x86@...nel.org>,
        "Neri, Ricardo" <ricardo.neri@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v9 25/29] x86/umip: Force a page fault when unable to
 copy emulated result to user

On Thu, Oct 26, 2017 at 12:59:55AM -0700, Andy Lutomirski wrote:
> On Tue, Oct 3, 2017 at 8:54 PM, Ricardo Neri
> <ricardo.neri-calderon@...ux.intel.com> wrote:
> > fixup_umip_exception() will be called from do_general_protection(). If the
> > former returns false, the latter will issue a SIGSEGV with SEND_SIG_PRIV.
> > However, when emulation is successful but the emulated result cannot be
> > copied to user space memory, it is more accurate to issue a SIGSEGV with
> > SEGV_MAPERR with the offending address. A new function, inspired in
> > force_sig_info_fault(), is introduced to model the page fault.
> 
> This code is slightly buggy (with, for example, PKRU, although the
> chance that anyone ever notices is about nil).  For an alternative
> approach, see current->thread.sig_on_uaccess_err, used in
> arch/x86/entry/vsyscall/vsyscall_64.c.  But I'm fine with this patch
> as is, too.

Thanks Andy, I will study the alternative you mention. Since you are OK
with this patch, I will submit v10 of this series to allow the review
of the series to continue.

BR,
Ricardo