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

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Date:   Mon, 30 Jan 2017 15:04:28 +0300
From:   Dmitry Safonov <dsafonov@...tuozzo.com>
To:     <linux-kernel@...r.kernel.org>
CC:     <0x7f454c46@...il.com>, Dmitry Safonov <dsafonov@...tuozzo.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        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: [PATCHv4 1/5] x86/mm: split arch_mmap_rnd() on compat/native versions

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 <dsafonov@...tuozzo.com>
---
 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
-	else
-		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
 
-	return rnd << PAGE_SHIFT;
+	return arch_native_rnd();
 }
 
 static unsigned long mmap_base(unsigned long rnd)
-- 
2.11.0