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Date:   Fri, 22 Mar 2019 03:42:22 -0400
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Christoph Hellwig <hch@...radead.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Palmer Dabbelt <palmer@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Cc:     Alexandre Ghiti <alex@...ti.fr>
Subject: [PATCH 1/4] 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.

This commit also takes the opportunity to:
- make use of is_compat_task instead of specific arm64 test
  test_thread_flag(TIF_32BIT), which allows more genericity and is
  equivalent.
- fix the case where stack randomization should not be taken into
  account.

It then introduces a new define ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
that can be defined by other architectures to benefit from those functions.

Suggested-by: Christoph Hellwig <hch@...radead.org>
Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
---
 arch/arm64/include/asm/processor.h |  2 +-
 arch/arm64/mm/mmap.c               | 72 ----------------------
 fs/binfmt_elf.c                    | 20 ------
 include/linux/mm.h                 |  2 +
 kernel/sysctl.c                    |  6 +-
 mm/util.c                          | 99 +++++++++++++++++++++++++++++-
 6 files changed, 105 insertions(+), 96 deletions(-)

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 5d9ce62bdebd..2358707c31ff 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -274,7 +274,7 @@ static inline void spin_lock_prefetch(const void *ptr)
 		     "nop") : : "p" (ptr));
 }
 
-#define HAVE_ARCH_PICK_MMAP_LAYOUT
+#define ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
 
 #endif
 
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index 842c8a5fcd53..c74224421216 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -31,78 +31,6 @@
 
 #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 (test_thread_flag(TIF_32BIT))
-		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_RND_MASK << PAGE_SHIFT) + stack_guard_gap;
-
-	/* 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.
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 7d09d125f148..045f3b29d264 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -662,26 +662,6 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
  * libraries.  There is no binary dependent code anywhere else.
  */
 
-#ifndef STACK_RND_MASK
-#define STACK_RND_MASK (0x7ff >> (PAGE_SHIFT - 12))	/* 8MB of VA */
-#endif
-
-static unsigned long randomize_stack_top(unsigned long stack_top)
-{
-	unsigned long random_variable = 0;
-
-	if (current->flags & PF_RANDOMIZE) {
-		random_variable = get_random_long();
-		random_variable &= STACK_RND_MASK;
-		random_variable <<= PAGE_SHIFT;
-	}
-#ifdef CONFIG_STACK_GROWSUP
-	return PAGE_ALIGN(stack_top) + random_variable;
-#else
-	return PAGE_ALIGN(stack_top) - random_variable;
-#endif
-}
-
 static int load_elf_binary(struct linux_binprm *bprm)
 {
 	struct file *interpreter = NULL; /* to shut gcc up */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 76769749b5a5..087824a5059f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2312,6 +2312,8 @@ extern int install_special_mapping(struct mm_struct *mm,
 				   unsigned long addr, unsigned long len,
 				   unsigned long flags, struct page **pages);
 
+unsigned long randomize_stack_top(unsigned long stack_top);
+
 extern unsigned long get_unmapped_area(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
 
 extern unsigned long mmap_region(struct file *file, unsigned long addr,
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index e5da394d1ca3..ac388f8ccbe4 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -269,7 +269,8 @@ 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(ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT)
 int sysctl_legacy_va_layout;
 #endif
 
@@ -1564,7 +1565,8 @@ static struct ctl_table vm_table[] = {
 		.proc_handler	= proc_dointvec,
 		.extra1		= &zero,
 	},
-#ifdef HAVE_ARCH_PICK_MMAP_LAYOUT
+#if defined(HAVE_ARCH_PICK_MMAP_LAYOUT) || \
+	defined(ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT)
 	{
 		.procname	= "legacy_va_layout",
 		.data		= &sysctl_legacy_va_layout,
diff --git a/mm/util.c b/mm/util.c
index d559bde497a9..5a0d4b1e17d9 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -14,6 +14,13 @@
 #include <linux/hugetlb.h>
 #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>
 
@@ -291,13 +298,103 @@ int vma_is_stack_for_current(struct vm_area_struct *vma)
 	return (vma->vm_start <= KSTK_ESP(t) && vma->vm_end >= KSTK_ESP(t));
 }
 
-#if defined(CONFIG_MMU) && !defined(HAVE_ARCH_PICK_MMAP_LAYOUT)
+#ifndef STACK_RND_MASK
+#define STACK_RND_MASK (0x7ff >> (PAGE_SHIFT - 12))     /* 8MB of VA */
+#endif
+
+unsigned long randomize_stack_top(unsigned long stack_top)
+{
+	unsigned long random_variable = 0;
+
+	if (current->flags & PF_RANDOMIZE) {
+		random_variable = get_random_long();
+		random_variable &= STACK_RND_MASK;
+		random_variable <<= PAGE_SHIFT;
+	}
+#ifdef CONFIG_STACK_GROWSUP
+	return PAGE_ALIGN(stack_top) + random_variable;
+#else
+	return PAGE_ALIGN(stack_top) - random_variable;
+#endif
+}
+
+#ifdef CONFIG_MMU
+#ifdef ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
+
+#ifdef CONFIG_ARCH_HAS_ELF_RANDOMIZE
+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;
+}
+#endif
+
+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;
+}
+
+#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(HAVE_ARCH_PICK_MMAP_LAYOUT)
 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 {
 	mm->mmap_base = TASK_UNMAPPED_BASE;
 	mm->get_unmapped_area = arch_get_unmapped_area;
 }
 #endif
+#endif /* CONFIG_MMU */
 
 /*
  * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
-- 
2.20.1

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