linux-kernel - Re: [v5 17/20] x86/umip: Force a page fault when unable to copy emulated result to user

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Date:   Sun, 5 Mar 2017 08:18:32 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        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>,
        Alexandre Julliard <julliard@...ehq.org>,
        Stas Sergeev <stsp@...t.ru>, Fenghua Yu <fenghua.yu@...el.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>, linux-msdos@...r.kernel.org,
        wine-devel@...ehq.org
Subject: Re: [v5 17/20] x86/umip: Force a page fault when unable to copy
 emulated result to user

On Fri, Mar 3, 2017 at 1:41 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 is inspired in
> force_sig_info_fault is introduced to model the page fault.
>
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
> ---
>  arch/x86/kernel/umip.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 43 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
> index e932f40..5b6a7cf 100644
> --- a/arch/x86/kernel/umip.c
> +++ b/arch/x86/kernel/umip.c
> @@ -170,6 +170,41 @@ static int __emulate_umip_insn(struct insn *insn, enum umip_insn umip_inst,
>  }
>
>  /**
> + * __force_sig_info_umip_fault - Force a SIGSEGV with SEGV_MAPERR
> + * @address:   Address that caused the signal
> + * @regs:      Register set containing the instruction pointer
> + *
> + * Force a SIGSEGV signal with SEGV_MAPERR as the error code. This function is
> + * intended to be used to provide a segmentation fault when the result of the
> + * UMIP emulation could not be copied to the user space memory.
> + *
> + * Return: none
> + */
> +static void __force_sig_info_umip_fault(void __user *address,
> +                                       struct pt_regs *regs)
> +{
> +       siginfo_t info;
> +       struct task_struct *tsk = current;
> +
> +       if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV)) {
> +               printk_ratelimited("%s[%d] umip emulation segfault ip:%lx sp:%lx error:%lx in %lx\n",
> +                                  tsk->comm, task_pid_nr(tsk), regs->ip,
> +                                  regs->sp, UMIP_PF_USER | UMIP_PF_WRITE,
> +                                  regs->ip);
> +       }
> +
> +       tsk->thread.cr2         = (unsigned long)address;
> +       tsk->thread.error_code  = UMIP_PF_USER | UMIP_PF_WRITE;

Please just move enum x86_pf_error_code into a header and rename the
fields X86_PF_USER, etc rather than duplicating it.

--Andy