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Subject[PATCH v2 3/5] arm: Use generic mmap top-down layout
Date
arm uses a top-down layout by default that fits the generic functions.
At the same time, this commit allows to fix the following problems:

- one uncovered and not fixed for arm here:
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1429066.html

- the use of TASK_SIZE instead of STACK_TOP in mmap_base which, when
address space of a task is 26 bits, would assign mmap base way too high.

Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
---
arch/arm/Kconfig | 1 +
arch/arm/include/asm/processor.h | 2 --
arch/arm/mm/mmap.c | 52 --------------------------------
3 files changed, 1 insertion(+), 54 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 850b4805e2d1..747101a8e989 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -28,6 +28,7 @@ config ARM
select ARCH_SUPPORTS_ATOMIC_RMW
select ARCH_USE_BUILTIN_BSWAP
select ARCH_USE_CMPXCHG_LOCKREF
+ select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
select ARCH_WANT_IPC_PARSE_VERSION
select BUILDTIME_EXTABLE_SORT if MMU
select CLONE_BACKWARDS
diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
index 57fe73ea0f72..944ef1fb1237 100644
--- a/arch/arm/include/asm/processor.h
+++ b/arch/arm/include/asm/processor.h
@@ -143,8 +143,6 @@ static inline void prefetchw(const void *ptr)
#endif
#endif

-#define HAVE_ARCH_PICK_MMAP_LAYOUT
-
#endif

#endif /* __ASM_ARM_PROCESSOR_H */
diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
index f866870db749..b8d912ac9e61 100644
--- a/arch/arm/mm/mmap.c
+++ b/arch/arm/mm/mmap.c
@@ -17,33 +17,6 @@
((((addr)+SHMLBA-1)&~(SHMLBA-1)) + \
(((pgoff)<<PAGE_SHIFT) & (SHMLBA-1)))

-/* gap between mmap and stack */
-#define MIN_GAP (128*1024*1024UL)
-#define MAX_GAP ((TASK_SIZE)/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;
-}
-
-static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
-{
- unsigned long gap = rlim_stack->rlim_cur;
-
- if (gap < MIN_GAP)
- gap = MIN_GAP;
- else if (gap > MAX_GAP)
- gap = MAX_GAP;
-
- return PAGE_ALIGN(TASK_SIZE - gap - rnd);
-}
-
/*
* We need to ensure that shared mappings are correctly aligned to
* avoid aliasing issues with VIPT caches. We need to ensure that
@@ -171,31 +144,6 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
return addr;
}

-unsigned long arch_mmap_rnd(void)
-{
- unsigned long rnd;
-
- rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
-
- return rnd << PAGE_SHIFT;
-}
-
-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;
- }
-}
-
/*
* You really shouldn't be using read() or write() on /dev/mem. This
* might go away in the future.
--
2.20.1
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