From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751552AbdBIXG4 (ORCPT ); Thu, 9 Feb 2017 18:06:56 -0500 Received: from mail-ua0-f181.google.com ([209.85.217.181]:34164 "EHLO mail-ua0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751368AbdBIXGx (ORCPT ); Thu, 9 Feb 2017 18:06:53 -0500 MIME-Version: 1.0 In-Reply-To: <20170209135525.qlwrmlo7njk3fsaq@pd.tnic> References: <20170130120432.6716-1-dsafonov@virtuozzo.com> <20170130120432.6716-2-dsafonov@virtuozzo.com> <20170209135525.qlwrmlo7njk3fsaq@pd.tnic> From: Andy Lutomirski Date: Thu, 9 Feb 2017 15:06:22 -0800 Message-ID: Subject: Re: [PATCHv4 1/5] x86/mm: split arch_mmap_rnd() on compat/native versions To: Borislav Petkov Cc: Dmitry Safonov , "linux-kernel@vger.kernel.org" , Dmitry Safonov <0x7f454c46@gmail.com>, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andy Lutomirski , Borislav Petkov , X86 ML , "linux-mm@kvack.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 9, 2017 at 5:55 AM, Borislav Petkov wrote: > On Mon, Jan 30, 2017 at 03:04:28PM +0300, Dmitry Safonov wrote: >> I need those arch_{native,compat}_rnd() to compute separately >> random factor for mmap() in compat syscalls for 64-bit binaries >> and vice-versa for native syscall in 32-bit compat binaries. >> They will be used in the following patches. >> >> Signed-off-by: Dmitry Safonov >> --- >> arch/x86/mm/mmap.c | 25 ++++++++++++++++--------- >> 1 file changed, 16 insertions(+), 9 deletions(-) >> >> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c >> index d2dc0438d654..42063e787717 100644 >> --- a/arch/x86/mm/mmap.c >> +++ b/arch/x86/mm/mmap.c >> @@ -65,20 +65,27 @@ static int mmap_is_legacy(void) >> return sysctl_legacy_va_layout; >> } >> >> -unsigned long arch_mmap_rnd(void) >> +#ifdef CONFIG_COMPAT >> +static unsigned long arch_compat_rnd(void) >> { >> - unsigned long rnd; >> + return (get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1)) >> + << PAGE_SHIFT; >> +} >> +#endif >> >> - if (mmap_is_ia32()) >> +static unsigned long arch_native_rnd(void) >> +{ >> + return (get_random_long() & ((1UL << mmap_rnd_bits) - 1)) << PAGE_SHIFT; >> +} >> + >> +unsigned long arch_mmap_rnd(void) >> +{ >> #ifdef CONFIG_COMPAT >> - rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1); >> -#else >> - rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1); >> + if (mmap_is_ia32()) >> + return arch_compat_rnd(); >> #endif > > I can't say that I'm thrilled about the ifdeffery this is adding. > > But I can't think of a cleaner approach at a quick glance, though - > that's generic and arch-specific code intertwined muck. Sad face. I can, but it could be considerably more churn: get rid of the compat/native split and do a 32-bit/64-bit split instead. > > -- > Regards/Gruss, > Boris. > > Good mailing practices for 400: avoid top-posting and trim the reply. -- Andy Lutomirski AMA Capital Management, LLC