arm64, mm: move generic mmap layout functions to mm

arm64 handles top-down mmap layout in a way that can be easily reused by
other architectures, so make it available in mm.  It then introduces a new
config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT that can be set by other
architectures to benefit from those functions.  Note that this new config
depends on MMU being enabled, if selected without MMU support, a warning
will be thrown.

Link: http://lkml.kernel.org/r/20190730055113.23635-5-alex@ghiti.frSigned-off-by: Alexandre Ghiti <alex@ghiti.fr>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: James Hogan <jhogan@kernel.org>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/Kconfig

@@ -706,6 +706,16 @@ config HAVE_ARCH_COMPAT_MMAP_BASES
 	  and vice-versa 32-bit applications to call 64-bit mmap().
 	  Required for applications doing different bitness syscalls.
 
+# This allows to use a set of generic functions to determine mmap base
+# address by giving priority to top-down scheme only if the process
+# is not in legacy mode (compat task, unlimited stack size or
+# sysctl_legacy_va_layout).
+# Architecture that selects this option can provide its own version of:
+# - STACK_RND_MASK
+config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
+	bool
+	depends on MMU
+
 config HAVE_COPY_THREAD_TLS
 	bool
 	help

arch/arm64/Kconfig

@@ -71,6 +71,7 @@ config ARM64
 	select ARCH_SUPPORTS_INT128 if GCC_VERSION >= 50000 || CC_IS_CLANG
 	select ARCH_SUPPORTS_NUMA_BALANCING
 	select ARCH_WANT_COMPAT_IPC_PARSE_VERSION if COMPAT
+	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
 	select ARCH_WANT_FRAME_POINTERS
 	select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36)
 	select ARCH_HAS_UBSAN_SANITIZE_ALL

arch/arm64/include/asm/processor.h

@@ -280,8 +280,6 @@ static inline void spin_lock_prefetch(const void *ptr)
 		     "nop") : : "p" (ptr));
 }
 
-#define HAVE_ARCH_PICK_MMAP_LAYOUT
-
 extern unsigned long __ro_after_init signal_minsigstksz; /* sigframe size */
 extern void __init minsigstksz_setup(void);
 

arch/arm64/mm/mmap.c

@@ -20,82 +20,6 @@
 
 #include <asm/cputype.h>
 
-/*
- * Leave enough space between the mmap area and the stack to honour ulimit in
- * the face of randomisation.
- */
-#define MIN_GAP (SZ_128M)
-#define MAX_GAP	(STACK_TOP/6*5)
-
-static int mmap_is_legacy(struct rlimit *rlim_stack)
-{
-	if (current->personality & ADDR_COMPAT_LAYOUT)
-		return 1;
-
-	if (rlim_stack->rlim_cur == RLIM_INFINITY)
-		return 1;
-
-	return sysctl_legacy_va_layout;
-}
-
-unsigned long arch_mmap_rnd(void)
-{
-	unsigned long rnd;
-
-#ifdef CONFIG_COMPAT
-	if (is_compat_task())
-		rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
-	else
-#endif
-		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
-	return rnd << PAGE_SHIFT;
-}
-
-static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
-{
-	unsigned long gap = rlim_stack->rlim_cur;
-	unsigned long pad = stack_guard_gap;
-
-	/* Account for stack randomization if necessary */
-	if (current->flags & PF_RANDOMIZE)
-		pad += (STACK_RND_MASK << PAGE_SHIFT);
-
-	/* Values close to RLIM_INFINITY can overflow. */
-	if (gap + pad > gap)
-		gap += pad;
-
-	if (gap < MIN_GAP)
-		gap = MIN_GAP;
-	else if (gap > MAX_GAP)
-		gap = MAX_GAP;
-
-	return PAGE_ALIGN(STACK_TOP - gap - rnd);
-}
-
-/*
- * This function, called very early during the creation of a new process VM
- * image, sets up which VM layout function to use:
- */
-void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
-{
-	unsigned long random_factor = 0UL;
-
-	if (current->flags & PF_RANDOMIZE)
-		random_factor = arch_mmap_rnd();
-
-	/*
-	 * Fall back to the standard layout if the personality bit is set, or
-	 * if the expected stack growth is unlimited:
-	 */
-	if (mmap_is_legacy(rlim_stack)) {
-		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
-		mm->get_unmapped_area = arch_get_unmapped_area;
-	} else {
-		mm->mmap_base = mmap_base(random_factor, rlim_stack);
-		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
-	}
-}
-
 /*
  * You really shouldn't be using read() or write() on /dev/mem.  This might go
  * away in the future.

kernel/sysctl.c

@@ -264,7 +264,8 @@ extern struct ctl_table epoll_table[];
 extern struct ctl_table firmware_config_table[];
 #endif
 
-#ifdef HAVE_ARCH_PICK_MMAP_LAYOUT
+#if defined(HAVE_ARCH_PICK_MMAP_LAYOUT) || \
+    defined(CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT)
 int sysctl_legacy_va_layout;
 #endif
 
@@ -1573,7 +1574,8 @@ static struct ctl_table vm_table[] = {
 		.proc_handler	= proc_dointvec,
 		.extra1		= SYSCTL_ZERO,
 	},
-#ifdef HAVE_ARCH_PICK_MMAP_LAYOUT
+#if defined(HAVE_ARCH_PICK_MMAP_LAYOUT) || \
+    defined(CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT)
 	{
 		.procname	= "legacy_va_layout",
 		.data		= &sysctl_legacy_va_layout,

mm/util.c

@@ -17,7 +17,12 @@
 #include <linux/vmalloc.h>
 #include <linux/userfaultfd_k.h>
 #include <linux/elf.h>
+#include <linux/elf-randomize.h>
+#include <linux/personality.h>
 #include <linux/random.h>
+#include <linux/processor.h>
+#include <linux/sizes.h>
+#include <linux/compat.h>
 
 #include <linux/uaccess.h>
 
@@ -315,7 +320,78 @@ unsigned long randomize_stack_top(unsigned long stack_top)
 #endif
 }
 
-#if defined(CONFIG_MMU) && !defined(HAVE_ARCH_PICK_MMAP_LAYOUT)
+#ifdef CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
+#ifdef CONFIG_ARCH_HAS_ELF_RANDOMIZE
+unsigned long arch_mmap_rnd(void)
+{
+	unsigned long rnd;
+
+#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
+	if (is_compat_task())
+		rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
+	else
+#endif /* CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS */
+		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
+
+	return rnd << PAGE_SHIFT;
+}
+#endif /* CONFIG_ARCH_HAS_ELF_RANDOMIZE */
+
+static int mmap_is_legacy(struct rlimit *rlim_stack)
+{
+	if (current->personality & ADDR_COMPAT_LAYOUT)
+		return 1;
+
+	if (rlim_stack->rlim_cur == RLIM_INFINITY)
+		return 1;
+
+	return sysctl_legacy_va_layout;
+}
+
+/*
+ * Leave enough space between the mmap area and the stack to honour ulimit in
+ * the face of randomisation.
+ */
+#define MIN_GAP		(SZ_128M)
+#define MAX_GAP		(STACK_TOP / 6 * 5)
+
+static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
+{
+	unsigned long gap = rlim_stack->rlim_cur;
+	unsigned long pad = stack_guard_gap;
+
+	/* Account for stack randomization if necessary */
+	if (current->flags & PF_RANDOMIZE)
+		pad += (STACK_RND_MASK << PAGE_SHIFT);
+
+	/* Values close to RLIM_INFINITY can overflow. */
+	if (gap + pad > gap)
+		gap += pad;
+
+	if (gap < MIN_GAP)
+		gap = MIN_GAP;
+	else if (gap > MAX_GAP)
+		gap = MAX_GAP;
+
+	return PAGE_ALIGN(STACK_TOP - gap - rnd);
+}
+
+void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
+{
+	unsigned long random_factor = 0UL;
+
+	if (current->flags & PF_RANDOMIZE)
+		random_factor = arch_mmap_rnd();
+
+	if (mmap_is_legacy(rlim_stack)) {
+		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
+		mm->get_unmapped_area = arch_get_unmapped_area;
+	} else {
+		mm->mmap_base = mmap_base(random_factor, rlim_stack);
+		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
+	}
+}
+#elif defined(CONFIG_MMU) && !defined(HAVE_ARCH_PICK_MMAP_LAYOUT)
 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 {
 	mm->mmap_base = TASK_UNMAPPED_BASE;