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

[Andy Lutomirski]

On Tue, Oct 3, 2017 at 8:54 PM, Ricardo Neri
<ricardo.neri-calderon@xxxxxxxxxxxxxxx> 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.