[PATCH RESEND 2/2] x86/mm: Randomize va with generic arch_pick_mmap_layout()

[sxwjean@me.com]

From: Xiongwei Song <sxwjean@gmail.com>

The code logic of arch_pick_mmap_layout() of x86 is basiclly same as
arch_pick_mmap_layout() in mm/util.c. Let's delete the function and
the related assistant functions in x86.

There are some differences between x86 and geneirc code:
- mmap_is_legacy(), there is no check for stack limit of 32 bits process
  in x86, while generic code does, which is suitable for x86 too.
- arch_randomize_brk(), it only randomized the brk with SZ_32M range
  for 32 bits and 64 bits processes, while the generic code randomizes brk
  with SZ_1G range for 64 bits process, which is suitable for x86 too.
- Implement is_compat_task(), which means 32 bits process in 64 bits
  kernel, to adapt generic implementation.
- The special implementation of x86 is the code with
  CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES enabled. I assume other archs will
  enable CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES in the future, so move the
  implementation to the generic part.

Hence select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT in x86 to use
generic arch_pick_mmap_layout(). Meanwhile, the ARCH_HAS_ELF_RANDOMIZE
can be enabled automatically, remove select for it.

Signed-off-by: Xiongwei Song <sxwjean@gmail.com>
---
 arch/x86/Kconfig                 |   2 +-
 arch/x86/include/asm/compat.h    |   7 +-
 arch/x86/include/asm/processor.h |   4 +-
 arch/x86/kernel/process.c        |   5 --
 arch/x86/mm/mmap.c               | 112 -------------------------------
 include/linux/compat.h           |   4 ++
 mm/util.c                        |  18 ++++-
 7 files changed, 29 insertions(+), 123 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index dad7f85dcdea..c081e6ff7f11 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -72,7 +72,6 @@ config X86
 	select ARCH_HAS_DEBUG_VM_PGTABLE	if !X86_PAE
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_EARLY_DEBUG		if KGDB
-	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_FAST_MULTIPLIER
 	select ARCH_HAS_FILTER_PGPROT
 	select ARCH_HAS_FORTIFY_SOURCE
@@ -114,6 +113,7 @@ config X86
 	select ARCH_USE_SYM_ANNOTATIONS
 	select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
 	select ARCH_WANT_DEFAULT_BPF_JIT	if X86_64
+	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
 	select ARCH_WANTS_DYNAMIC_TASK_STRUCT
 	select ARCH_WANTS_NO_INSTR
 	select ARCH_WANT_HUGE_PMD_SHARE
diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h
index 7516e4199b3c..c697e377644d 100644
--- a/arch/x86/include/asm/compat.h
+++ b/arch/x86/include/asm/compat.h
@@ -151,6 +151,11 @@ struct compat_shmid64_ds {
 	compat_ulong_t __unused5;
 };
 
+static inline int is_compat_task(void)
+{
+	return IS_ENABLED(CONFIG_COMPAT) && test_thread_flag(TIF_32BIT);
+}
+
 #ifdef CONFIG_X86_X32_ABI
 #define COMPAT_USE_64BIT_TIME \
 	(!!(task_pt_regs(current)->orig_ax & __X32_SYSCALL_BIT))
@@ -165,12 +170,12 @@ static inline bool in_x32_syscall(void)
 	return false;
 }
 
+#ifdef CONFIG_COMPAT
 static inline bool in_32bit_syscall(void)
 {
 	return in_ia32_syscall() || in_x32_syscall();
 }
 
-#ifdef CONFIG_COMPAT
 static inline bool in_compat_syscall(void)
 {
 	return in_32bit_syscall();
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 9ad2acaaae9b..c28a36ee6eb0 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -708,7 +708,6 @@ extern int			bootloader_version;
 
 extern char			ignore_fpu_irq;
 
-#define HAVE_ARCH_PICK_MMAP_LAYOUT 1
 #define ARCH_HAS_PREFETCHW
 #define ARCH_HAS_SPINLOCK_PREFETCH
 
@@ -785,6 +784,9 @@ extern void start_thread(struct pt_regs *regs, unsigned long new_ip,
  */
 #define __TASK_UNMAPPED_BASE(task_size)	(PAGE_ALIGN(task_size / 3))
 #define TASK_UNMAPPED_BASE		__TASK_UNMAPPED_BASE(TASK_SIZE_LOW)
+#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
+#define TASK_UNMAPPED_COMPAT_BASE __TASK_UNMAPPED_BASE(task_size_32bit())
+#endif
 
 #define KSTK_EIP(task)		(task_pt_regs(task)->ip)
 
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 1d9463e3096b..1e747d34c18d 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -931,11 +931,6 @@ unsigned long arch_align_stack(unsigned long sp)
 	return sp & ~0xf;
 }
 
-unsigned long arch_randomize_brk(struct mm_struct *mm)
-{
-	return randomize_page(mm->brk, 0x02000000);
-}
-
 /*
  * Called from fs/proc with a reference on @p to find the function
  * which called into schedule(). This needs to be done carefully
diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index c90c20904a60..daf65cc5e5b1 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -38,118 +38,6 @@ unsigned long task_size_64bit(int full_addr_space)
 	return full_addr_space ? TASK_SIZE_MAX : DEFAULT_MAP_WINDOW;
 }
 
-static unsigned long stack_maxrandom_size(unsigned long task_size)
-{
-	unsigned long max = 0;
-	if (current->flags & PF_RANDOMIZE) {
-		max = (-1UL) & __STACK_RND_MASK(task_size == task_size_32bit());
-		max <<= PAGE_SHIFT;
-	}
-
-	return max;
-}
-
-#ifdef CONFIG_COMPAT
-# define mmap32_rnd_bits  mmap_rnd_compat_bits
-# define mmap64_rnd_bits  mmap_rnd_bits
-#else
-# define mmap32_rnd_bits  mmap_rnd_bits
-# define mmap64_rnd_bits  mmap_rnd_bits
-#endif
-
-#define SIZE_128M    (128 * 1024 * 1024UL)
-
-static int mmap_is_legacy(void)
-{
-	if (current->personality & ADDR_COMPAT_LAYOUT)
-		return 1;
-
-	return sysctl_legacy_va_layout;
-}
-
-static unsigned long arch_rnd(unsigned int rndbits)
-{
-	if (!(current->flags & PF_RANDOMIZE))
-		return 0;
-	return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
-}
-
-unsigned long arch_mmap_rnd(void)
-{
-	return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
-}
-
-static unsigned long mmap_base(unsigned long rnd, unsigned long task_size,
-			       struct rlimit *rlim_stack)
-{
-	unsigned long gap = rlim_stack->rlim_cur;
-	unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap;
-	unsigned long gap_min, gap_max;
-
-	/* Values close to RLIM_INFINITY can overflow. */
-	if (gap + pad > gap)
-		gap += pad;
-
-	/*
-	 * Top of mmap area (just below the process stack).
-	 * Leave an at least ~128 MB hole with possible stack randomization.
-	 */
-	gap_min = SIZE_128M;
-	gap_max = (task_size / 6) * 5;
-
-	if (gap < gap_min)
-		gap = gap_min;
-	else if (gap > gap_max)
-		gap = gap_max;
-
-	return PAGE_ALIGN(task_size - gap - rnd);
-}
-
-static unsigned long mmap_legacy_base(unsigned long rnd,
-				      unsigned long task_size)
-{
-	return __TASK_UNMAPPED_BASE(task_size) + rnd;
-}
-
-/*
- * This function, called very early during the creation of a new
- * process VM image, sets up which VM layout function to use:
- */
-static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base,
-		unsigned long random_factor, unsigned long task_size,
-		struct rlimit *rlim_stack)
-{
-	*legacy_base = mmap_legacy_base(random_factor, task_size);
-	if (mmap_is_legacy())
-		*base = *legacy_base;
-	else
-		*base = mmap_base(random_factor, task_size, rlim_stack);
-}
-
-void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
-{
-	if (mmap_is_legacy())
-		mm->get_unmapped_area = arch_get_unmapped_area;
-	else
-		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
-
-	arch_pick_mmap_base(&mm->mmap_base, &mm->mmap_legacy_base,
-			arch_rnd(mmap64_rnd_bits), task_size_64bit(0),
-			rlim_stack);
-
-#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
-	/*
-	 * The mmap syscall mapping base decision depends solely on the
-	 * syscall type (64-bit or compat). This applies for 64bit
-	 * applications and 32bit applications. The 64bit syscall uses
-	 * mmap_base, the compat syscall uses mmap_compat_base.
-	 */
-	arch_pick_mmap_base(&mm->mmap_compat_base, &mm->mmap_compat_legacy_base,
-			arch_rnd(mmap32_rnd_bits), task_size_32bit(),
-			rlim_stack);
-#endif
-}
-
 unsigned long get_mmap_base(int is_legacy)
 {
 	struct mm_struct *mm = current->mm;
diff --git a/include/linux/compat.h b/include/linux/compat.h
index 1c758b0e0359..0f7cc94f9b3f 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -946,6 +946,10 @@ static inline bool in_compat_syscall(void) { return false; }
 
 #endif /* CONFIG_COMPAT */
 
+#ifndef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
+static inline bool in_32bit_syscall(void) { return false; }
+#endif
+
 #define BITS_PER_COMPAT_LONG    (8*sizeof(compat_long_t))
 
 #define BITS_TO_COMPAT_LONGS(bits) DIV_ROUND_UP(bits, BITS_PER_COMPAT_LONG)
diff --git a/mm/util.c b/mm/util.c
index 4ac87f1b30f1..8932388c96a3 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -357,8 +357,9 @@ unsigned long arch_mmap_rnd(void)
 {
 	unsigned long rnd;
 
-#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS
-	if (is_compat_task())
+#if defined(CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS) \
+	|| defined(CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES)
+	if (is_compat_task() || in_32bit_syscall())
 		rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
 	else
 #endif /* CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS */
@@ -413,13 +414,24 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 	if (current->flags & PF_RANDOMIZE)
 		random_factor = arch_mmap_rnd();
 
+	mm->mmap_legacy_base = TASK_UNMAPPED_BASE + random_factor;
 	if (mmap_is_legacy(rlim_stack)) {
-		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
+		mm->mmap_base = mm->mmap_legacy_base;
 		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;
 	}
+
+#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
+	if (mmap_is_legacy(rlim_stack)) {
+		mm->mmap_compat_legacy_base =
+			TASK_UNMAPPED_COMPAT_BASE + random_factor;
+		mm->mmap_compat_base = mm->mmap_compat_legacy_base;
+	} else {
+		mm->mmap_compat_base = mmap_base(random_factor, rlim_stack);
+	}
+#endif
 }
 #elif defined(CONFIG_MMU) && !defined(HAVE_ARCH_PICK_MMAP_LAYOUT)
 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
-- 
2.30.2