From:   Christophe Leroy <christophe.leroy@csgroup.eu>
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>
CC:     Christophe Leroy <christophe.leroy@csgroup.eu>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: [PATCH 2/2] powerpc: Simplify and move arch_randomize_brk()
Thread-Topic: [PATCH 2/2] powerpc: Simplify and move arch_randomize_brk()
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Date:   Wed, 8 Dec 2021 14:32:45 +0000
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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: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 Applies on top of series "powerpc: Make hash MMU code build configurable"

 arch/powerpc/kernel/process.c         | 41 ---------------------------
 arch/powerpc/mm/book3s64/hash_utils.c | 19 +++++++++++++
 2 files changed, 19 insertions(+), 41 deletions(-)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 984813a4d5dc..e7f809bdd433 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -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;
-}
-
diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index eced266dc5e9..b179a001bfa4 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -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>
@@ -2185,3 +2187,20 @@ 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);
+}
-- 
2.33.1