Commit 3ba4289a authored by Christophe Leroy's avatar Christophe Leroy Committed by Michael Ellerman
Browse files

powerpc: Simplify and move arch_randomize_brk() 



arch_randomize_brk() is only needed for hash on book3s/64, for other
platforms the one provided by the default mmap layout is good enough.

Move it to hash_utils.c and use randomize_page() like the generic one.

And properly opt out the radix case instead of making an assumption
on mmu_highuser_ssize.

Also change to a 32M range like most other architectures instead of 8M.

Signed-off-by: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/eafa4d18ec8ac7b98dd02b40181e61643707cc7c.1649523076.git.christophe.leroy@csgroup.eu
parent 36e5f9ee

arch/powerpc/kernel/process.c

+0 −41
Original line number Diff line number Diff line
@@ -34,10 +34,8 @@ 
#include <linux/ftrace.h>

#include <linux/kernel_stat.h>

#include <linux/personality.h>

#include <linux/random.h>

#include <linux/hw_breakpoint.h>

#include <linux/uaccess.h>

#include <linux/elf-randomize.h>

#include <linux/pkeys.h>

#include <linux/seq_buf.h>
@@ -2313,42 +2311,3 @@ unsigned long arch_align_stack(unsigned long sp) 
		sp -= get_random_int() & ~PAGE_MASK;

	return sp & ~0xf;

}
 


static inline unsigned long brk_rnd(void)

{

        unsigned long rnd = 0;



	/* 8MB for 32bit, 1GB for 64bit */

	if (is_32bit_task())

		rnd = (get_random_long() % (1UL<<(23-PAGE_SHIFT)));

	else

		rnd = (get_random_long() % (1UL<<(30-PAGE_SHIFT)));



	return rnd << PAGE_SHIFT;

}



unsigned long arch_randomize_brk(struct mm_struct *mm)

{

	unsigned long base = mm->brk;

	unsigned long ret;



#ifdef CONFIG_PPC_BOOK3S_64

	/*

	 * If we are using 1TB segments and we are allowed to randomise

	 * the heap, we can put it above 1TB so it is backed by a 1TB

	 * segment. Otherwise the heap will be in the bottom 1TB

	 * which always uses 256MB segments and this may result in a

	 * performance penalty.

	 */

	if (!radix_enabled() && !is_32bit_task() && (mmu_highuser_ssize == MMU_SEGSIZE_1T))

		base = max_t(unsigned long, mm->brk, 1UL << SID_SHIFT_1T);

#endif



	ret = PAGE_ALIGN(base + brk_rnd());



	if (ret < mm->brk)

		return mm->brk;



	return ret;

}

arch/powerpc/mm/book3s64/hash_utils.c

+19 −0
Original line number Diff line number Diff line
@@ -37,6 +37,8 @@ 
#include <linux/cpu.h>

#include <linux/pgtable.h>

#include <linux/debugfs.h>

#include <linux/random.h>

#include <linux/elf-randomize.h>



#include <asm/interrupt.h>

#include <asm/processor.h>
@@ -2133,3 +2135,20 @@ void __init print_system_hash_info(void) 
	if (htab_hash_mask)

		pr_info("htab_hash_mask    = 0x%lx\n", htab_hash_mask);

}



unsigned long arch_randomize_brk(struct mm_struct *mm)

{

	/*

	 * If we are using 1TB segments and we are allowed to randomise

	 * the heap, we can put it above 1TB so it is backed by a 1TB

	 * segment. Otherwise the heap will be in the bottom 1TB

	 * which always uses 256MB segments and this may result in a

	 * performance penalty.

	 */

	if (is_32bit_task())

		return randomize_page(mm->brk, SZ_32M);

	else if (!radix_enabled() && mmu_highuser_ssize == MMU_SEGSIZE_1T)

		return randomize_page(max_t(unsigned long, mm->brk, SZ_1T), SZ_1G);

	else

		return randomize_page(mm->brk, SZ_1G);

}