linux-kernel - Re: [PATCHv4 1/5] x86/mm: split arch_mmap

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Date:   Fri, 10 Feb 2017 21:10:30 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Borislav Petkov <bp@...en8.de>
cc:     Dmitry Safonov <dsafonov@...tuozzo.com>,
        linux-kernel@...r.kernel.org, 0x7f454c46@...il.com,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...e.de>, x86@...nel.org,
        linux-mm@...ck.org
Subject: Re: [PATCHv4 1/5] x86/mm: split arch_mmap_rnd() on compat/native
 versions

On Thu, 9 Feb 2017, Borislav Petkov wrote:
> 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.

It's trivial enough to do ....

Thanks,

	tglx

---
 arch/x86/mm/mmap.c |   22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -55,6 +55,10 @@ static unsigned long stack_maxrandom_siz
 #define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
 #define MAX_GAP (TASK_SIZE/6*5)
 
+#ifndef CONFIG_COMPAT
+# define mmap_rnd_compat_bits	mmap_rnd_bits
+#endif
+
 static int mmap_is_legacy(void)
 {
 	if (current->personality & ADDR_COMPAT_LAYOUT)
@@ -66,20 +70,14 @@ static int mmap_is_legacy(void)
 	return sysctl_legacy_va_layout;
 }
 
-unsigned long arch_mmap_rnd(void)
+static unsigned long arch_rnd(unsigned int rndbits)
 {
-	unsigned long rnd;
-
-	if (mmap_is_ia32())
-#ifdef CONFIG_COMPAT
-		rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
-#else
-		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
-#endif
-	else
-		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
+	return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
+}
 
-	return rnd << PAGE_SHIFT;
+unsigned long arch_mmap_rnd(void)
+{
+	return arch_rnd(mmap_is_ia32() ? mmap_rnd_compat_bits : mmap_rnd_bits);
 }
 
 static unsigned long mmap_base(unsigned long rnd)