[PATCH v10 13/13] powerpc: Simplify and move arch_randomize_brk()

Christophe Leroy
2022-04-09T17:19:49Z

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>
---
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 43ecad8f9564..72a3eca02449 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>
@@ -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);
+}
--
2.35.1