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    Subject[v6 PATCH 18/21] x86/umip: Force a page fault when unable to copy emulated result to user
    Date
    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@linux.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 e64d8e5..bd06e26 100644
    --- a/arch/x86/kernel/umip.c
    +++ b/arch/x86/kernel/umip.c
    @@ -163,6 +163,41 @@ 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:%x in %lx\n",
    + tsk->comm, task_pid_nr(tsk), regs->ip,
    + regs->sp, X86_PF_USER | X86_PF_WRITE,
    + regs->ip);
    + }
    +
    + tsk->thread.cr2 = (unsigned long)address;
    + tsk->thread.error_code = X86_PF_USER | X86_PF_WRITE;
    + tsk->thread.trap_nr = X86_TRAP_PF;
    +
    + info.si_signo = SIGSEGV;
    + info.si_errno = 0;
    + info.si_code = SEGV_MAPERR;
    + info.si_addr = address;
    + force_sig_info(SIGSEGV, &info, tsk);
    +}
    +
    +/**
    * fixup_umip_exception - Fixup #GP faults caused by UMIP
    * @regs: Registers as saved when entering the #GP trap
    *
    @@ -247,8 +282,14 @@ bool fixup_umip_exception(struct pt_regs *regs)
    } else {
    uaddr = insn_get_addr_ref(&insn, regs);
    nr_copied = copy_to_user(uaddr, dummy_data, dummy_data_size);
    - if (nr_copied > 0)
    - return false;
    + if (nr_copied > 0) {
    + /*
    + * If copy fails, send a signal and tell caller that
    + * fault was fixed up
    + */
    + __force_sig_info_umip_fault(uaddr, regs);
    + return true;
    + }
    }

    /* increase IP to let the program keep going */
    --
    2.9.3
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