[PATCHv6 2/5] x86/mm: add task_size parameter to mmap_base()

Dmitry Safonov
2017-03-06T14:21:24Z

To correctly handle 32-bit and 64-bit mmap() syscalls, we need different
mmap bases to start allocation from. So, introduce mmap_legacy_base()
helper and change mmap_base() to return base address according to
specified task size.
It'll prepare the mmap base computing code for splitting mmap_base
on two bases: for 64-bit syscall and for 32-bit syscalls.

Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
---
arch/x86/include/asm/elf.h | 24 ++++++++++---------
arch/x86/include/asm/processor.h | 4 +++-
arch/x86/mm/mmap.c | 50 +++++++++++++++++++++++++---------------
3 files changed, 48 insertions(+), 30 deletions(-)

diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 9d49c18b5ea9..b908141cf0c4 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -293,8 +293,19 @@ do { \
} \
} while (0)

+/*
+ * True on X86_32 or when emulating IA32 on X86_64
+ */
+static inline int mmap_is_ia32(void)
+{
+ return IS_ENABLED(CONFIG_X86_32) ||
+ (IS_ENABLED(CONFIG_COMPAT) &&
+ test_thread_flag(TIF_ADDR32));
+}
+
#ifdef CONFIG_X86_32

+#define __STACK_RND_MASK(is32bit) (0x7ff)
#define STACK_RND_MASK (0x7ff)

#define ARCH_DLINFO ARCH_DLINFO_IA32
@@ -304,7 +315,8 @@ do { \
#else /* CONFIG_X86_32 */

/* 1GB for 64bit, 8MB for 32bit */
-#define STACK_RND_MASK (test_thread_flag(TIF_ADDR32) ? 0x7ff : 0x3fffff)
+#define __STACK_RND_MASK(is32bit) ((is32bit) ? 0x7ff : 0x3fffff)
+#define STACK_RND_MASK __STACK_RND_MASK(mmap_is_ia32())

#define ARCH_DLINFO \
do { \
@@ -348,16 +360,6 @@ extern int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
int uses_interp);
#define compat_arch_setup_additional_pages compat_arch_setup_additional_pages

-/*
- * True on X86_32 or when emulating IA32 on X86_64
- */
-static inline int mmap_is_ia32(void)
-{
- return IS_ENABLED(CONFIG_X86_32) ||
- (IS_ENABLED(CONFIG_COMPAT) &&
- test_thread_flag(TIF_ADDR32));
-}
-
/* Do not change the values. See get_align_mask() */
enum align_flags {
ALIGN_VA_32 = BIT(0),
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index f385eca5407a..7caa2ac50ea2 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -797,6 +797,7 @@ static inline void spin_lock_prefetch(const void *x)
/*
* User space process size: 3GB (default).
*/
+#define IA32_PAGE_OFFSET PAGE_OFFSET
#define TASK_SIZE PAGE_OFFSET
#define TASK_SIZE_MAX TASK_SIZE
#define STACK_TOP TASK_SIZE
@@ -873,7 +874,8 @@ extern void start_thread(struct pt_regs *regs, unsigned long new_ip,
* This decides where the kernel will search for a free chunk of vm
* space during mmap's.
*/
-#define TASK_UNMAPPED_BASE (PAGE_ALIGN(TASK_SIZE / 3))
+#define __TASK_UNMAPPED_BASE(task_size) (PAGE_ALIGN(task_size / 3))
+#define TASK_UNMAPPED_BASE __TASK_UNMAPPED_BASE(TASK_SIZE)

#define KSTK_EIP(task) (task_pt_regs(task)->ip)

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index f31ed7097d0b..1e9cb945dca1 100644
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -36,25 +36,23 @@ struct va_alignment __read_mostly va_align = {
.flags = -1,
};

-static unsigned long stack_maxrandom_size(void)
+static inline unsigned long tasksize_32bit(void)
+{
+ return IA32_PAGE_OFFSET;
+}
+
+static unsigned long stack_maxrandom_size(unsigned long task_size)
{
unsigned long max = 0;
if ((current->flags & PF_RANDOMIZE) &&
!(current->personality & ADDR_NO_RANDOMIZE)) {
- max = ((-1UL) & STACK_RND_MASK) << PAGE_SHIFT;
+ max = (-1UL) & __STACK_RND_MASK(task_size == tasksize_32bit());
+ max <<= PAGE_SHIFT;
}

return max;
}

-/*
- * Top of mmap area (just below the process stack).
- *
- * Leave an at least ~128 MB hole with possible stack randomization.
- */
-#define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
-#define MAX_GAP (TASK_SIZE/6*5)
-
#ifdef CONFIG_COMPAT
# define mmap32_rnd_bits mmap_rnd_compat_bits
# define mmap64_rnd_bits mmap_rnd_bits
@@ -63,6 +61,8 @@ static unsigned long stack_maxrandom_size(void)
# 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)
@@ -84,16 +84,30 @@ 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)
+static unsigned long mmap_base(unsigned long rnd, unsigned long task_size)
{
unsigned long gap = rlimit(RLIMIT_STACK);
+ unsigned long gap_min, gap_max;
+
+ /*
+ * Top of mmap area (just below the process stack).
+ * Leave an at least ~128 MB hole with possible stack randomization.
+ */
+ gap_min = SIZE_128M + stack_maxrandom_size(task_size);
+ gap_max = (task_size / 6) * 5;

- if (gap < MIN_GAP)
- gap = MIN_GAP;
- else if (gap > MAX_GAP)
- gap = MAX_GAP;
+ if (gap < gap_min)
+ gap = gap_min;
+ else if (gap > gap_max)
+ gap = gap_max;

- return PAGE_ALIGN(TASK_SIZE - gap - rnd);
+ 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;
}

/*
@@ -107,13 +121,13 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
if (current->flags & PF_RANDOMIZE)
random_factor = arch_mmap_rnd();

- mm->mmap_legacy_base = TASK_UNMAPPED_BASE + random_factor;
+ mm->mmap_legacy_base = mmap_legacy_base(random_factor, TASK_SIZE);

if (mmap_is_legacy()) {
mm->mmap_base = mm->mmap_legacy_base;
mm->get_unmapped_area = arch_get_unmapped_area;
} else {
- mm->mmap_base = mmap_base(random_factor);
+ mm->mmap_base = mmap_base(random_factor, TASK_SIZE);
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
}
}
--
2.11.1