[PATCH v4 09/10] powerpc/mm: Convert to default topdown mmap layout

Christophe Leroy
2021-12-08T17:18:48Z

Select CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT and
remove arch/powerpc/mm/mmap.c

This change provides standard randomisation of mmaps.

See commit 8b8addf891de ("x86/mm/32: Enable full randomization on i386
and X86_32") for all the benefits of mmap randomisation.

Comparison between powerpc implementation and the generic one:
- mmap_is_legacy() is identical.
- arch_mmap_rnd() does exactly the same allthough it's written
slightly differently.
- MIN_GAP and MAX_GAP are identical.
- mmap_base() does the same but uses STACK_RND_MASK which provides
the same values as stack_maxrandom_size().
- arch_pick_mmap_layout() is almost identical. The only difference
is that it also adds the random factor to mm->mmap_base in legacy mode.

That last point is what provides the standard randomisation of mmaps.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
arch/powerpc/Kconfig | 2 +-
arch/powerpc/include/asm/processor.h | 2 -
arch/powerpc/mm/Makefile | 2 +-
arch/powerpc/mm/mmap.c | 105 ---------------------------
4 files changed, 2 insertions(+), 109 deletions(-)
delete mode 100644 arch/powerpc/mm/mmap.c

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 0631c9241af3..b4ae3d8bde46 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -122,7 +122,6 @@ config PPC
select ARCH_HAS_DEBUG_WX if STRICT_KERNEL_RWX
select ARCH_HAS_DEVMEM_IS_ALLOWED
select ARCH_HAS_DMA_MAP_DIRECT if PPC_PSERIES
- select ARCH_HAS_ELF_RANDOMIZE
select ARCH_HAS_FORTIFY_SOURCE
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_HAS_HUGEPD if HUGETLB_PAGE
@@ -158,6 +157,7 @@ config PPC
select ARCH_USE_MEMTEST
select ARCH_USE_QUEUED_RWLOCKS if PPC_QUEUED_SPINLOCKS
select ARCH_USE_QUEUED_SPINLOCKS if PPC_QUEUED_SPINLOCKS
+ select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
select ARCH_WANT_IPC_PARSE_VERSION
select ARCH_WANT_IRQS_OFF_ACTIVATE_MM
select ARCH_WANT_LD_ORPHAN_WARN
diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index 2c8686d9e964..873adaab20c8 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -392,8 +392,6 @@ static inline void prefetchw(const void *x)

#define spin_lock_prefetch(x) prefetchw(x)

-#define HAVE_ARCH_PICK_MMAP_LAYOUT
-
/* asm stubs */
extern unsigned long isa300_idle_stop_noloss(unsigned long psscr_val);
extern unsigned long isa300_idle_stop_mayloss(unsigned long psscr_val);
diff --git a/arch/powerpc/mm/Makefile b/arch/powerpc/mm/Makefile
index d4c20484dad9..503a6e249940 100644
--- a/arch/powerpc/mm/Makefile
+++ b/arch/powerpc/mm/Makefile
@@ -5,7 +5,7 @@

ccflags-$(CONFIG_PPC64) := $(NO_MINIMAL_TOC)

-obj-y := fault.o mem.o pgtable.o mmap.o maccess.o pageattr.o \
+obj-y := fault.o mem.o pgtable.o maccess.o pageattr.o \
init_$(BITS).o pgtable_$(BITS).o \
pgtable-frag.o ioremap.o ioremap_$(BITS).o \
init-common.o mmu_context.o drmem.o \
diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
deleted file mode 100644
index 5972d619d274..000000000000
--- a/arch/powerpc/mm/mmap.c
+++ /dev/null
@@ -1,105 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-/*
- * flexible mmap layout support
- *
- * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
- * All Rights Reserved.
- *
- * Started by Ingo Molnar <mingo@elte.hu>
- */
-
-#include <linux/personality.h>
-#include <linux/mm.h>
-#include <linux/random.h>
-#include <linux/sched/signal.h>
-#include <linux/sched/mm.h>
-#include <linux/elf-randomize.h>
-#include <linux/security.h>
-#include <linux/mman.h>
-
-/*
- * Top of mmap area (just below the process stack).
- *
- * Leave at least a ~128 MB hole.
- */
-#define MIN_GAP (128*1024*1024)
-#define MAX_GAP (TASK_SIZE/6*5)
-
-static inline 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 shift, rnd;
-
- shift = mmap_rnd_bits;
-#ifdef CONFIG_COMPAT
- if (is_32bit_task())
- shift = mmap_rnd_compat_bits;
-#endif
- rnd = get_random_long() % (1ul << shift);
-
- return rnd << PAGE_SHIFT;
-}
-
-static inline unsigned long stack_maxrandom_size(void)
-{
- if (!(current->flags & PF_RANDOMIZE))
- return 0;
-
- /* 8MB for 32bit, 1GB for 64bit */
- if (is_32bit_task())
- return (1<<23);
- else
- return (1<<30);
-}
-
-static inline unsigned long mmap_base(unsigned long rnd,
- struct rlimit *rlim_stack)
-{
- unsigned long gap = rlim_stack->rlim_cur;
- unsigned long pad = stack_maxrandom_size() + 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(DEFAULT_MAP_WINDOW - 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;
- 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;
- }
-}
--
2.33.1