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Commit dba79c3d authored by Alexandre Ghiti's avatar Alexandre Ghiti Committed by Linus Torvalds
Browse files

arm: use generic mmap top-down layout and brk randomization 

arm uses a top-down mmap layout by default that exactly fits the generic
functions, so get rid of arch specific code and use the generic version by
selecting ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT.

As ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT selects ARCH_HAS_ELF_RANDOMIZE,
use the generic version of arch_randomize_brk since it also fits.  Note
that this commit also removes the possibility for arm to have elf
randomization and no MMU: without MMU, the security added by randomization
is worth nothing.

Note that it is safe to remove STACK_RND_MASK since it matches the default
value.

Link: http://lkml.kernel.org/r/20190730055113.23635-9-alex@ghiti.fr


Signed-off-by: default avatarAlexandre Ghiti <alex@ghiti.fr>
Acked-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarLuis Chamberlain <mcgrof@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: James Hogan <jhogan@kernel.org>
Cc: Palmer Dabbelt <palmer@sifive.com>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 86e568e9

arch/arm/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -34,6 +34,7 @@ config ARM 
	select ARCH_SUPPORTS_ATOMIC_RMW

	select ARCH_USE_BUILTIN_BSWAP

	select ARCH_USE_CMPXCHG_LOCKREF

	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU

	select ARCH_WANT_IPC_PARSE_VERSION

	select BINFMT_FLAT_ARGVP_ENVP_ON_STACK

	select BUILDTIME_EXTABLE_SORT if MMU

arch/arm/include/asm/processor.h

+0 −2
Original line number Diff line number Diff line
@@ -140,8 +140,6 @@ static inline void prefetchw(const void *ptr) 
#endif

#endif



#define HAVE_ARCH_PICK_MMAP_LAYOUT



#endif



#endif /* __ASM_ARM_PROCESSOR_H */

arch/arm/kernel/process.c

+0 −5
Original line number Diff line number Diff line
@@ -319,11 +319,6 @@ unsigned long get_wchan(struct task_struct *p) 
	return 0;

}



unsigned long arch_randomize_brk(struct mm_struct *mm)

{

	return randomize_page(mm->brk, 0x02000000);

}



#ifdef CONFIG_MMU

#ifdef CONFIG_KUSER_HELPERS

/*

arch/arm/mm/mmap.c

+0 −62
Original line number Diff line number Diff line
@@ -17,43 +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		((STACK_TOP)/6*5)

#define STACK_RND_MASK	(0x7ff >> (PAGE_SHIFT - 12))



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;

	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);

}



/*

 * We need to ensure that shared mappings are correctly aligned to

 * avoid aliasing issues with VIPT caches.  We need to ensure that
@@ -181,31 +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.