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Subject[PATCH v5 07/17] powerpc: align stack to 2 * THREAD_SIZE with VMAP_STACK
Date
In order to ease stack overflow detection, align
stack to 2 * THREAD_SIZE when using VMAP_STACK.
This allows overflow detection using a single bit check.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
arch/powerpc/include/asm/thread_info.h | 13 +++++++++++++
arch/powerpc/kernel/setup_32.c | 2 +-
arch/powerpc/kernel/setup_64.c | 2 +-
arch/powerpc/kernel/vmlinux.lds.S | 2 +-
4 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index 488d5c4670ff..a2270749b282 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -22,6 +22,19 @@

#define THREAD_SIZE (1 << THREAD_SHIFT)

+/*
+ * By aligning VMAP'd stacks to 2 * THREAD_SIZE, we can detect overflow by
+ * checking sp & (1 << THREAD_SHIFT), which we can do cheaply in the entry
+ * assembly.
+ */
+#ifdef CONFIG_VMAP_STACK
+#define THREAD_ALIGN_SHIFT (THREAD_SHIFT + 1)
+#else
+#define THREAD_ALIGN_SHIFT THREAD_SHIFT
+#endif
+
+#define THREAD_ALIGN (1 << THREAD_ALIGN_SHIFT)
+
#ifndef __ASSEMBLY__
#include <linux/cache.h>
#include <asm/processor.h>
diff --git a/arch/powerpc/kernel/setup_32.c b/arch/powerpc/kernel/setup_32.c
index dcffe927f5b9..f014c4f7a337 100644
--- a/arch/powerpc/kernel/setup_32.c
+++ b/arch/powerpc/kernel/setup_32.c
@@ -140,7 +140,7 @@ arch_initcall(ppc_init);

static void *__init alloc_stack(void)
{
- void *ptr = memblock_alloc(THREAD_SIZE, THREAD_SIZE);
+ void *ptr = memblock_alloc(THREAD_SIZE, THREAD_ALIGN);

if (!ptr)
panic("cannot allocate %d bytes for stack at %pS\n",
diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 6104917a282d..e05e6dd67ae6 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c
@@ -633,7 +633,7 @@ static void *__init alloc_stack(unsigned long limit, int cpu)

BUILD_BUG_ON(STACK_INT_FRAME_SIZE % 16);

- ptr = memblock_alloc_try_nid(THREAD_SIZE, THREAD_SIZE,
+ ptr = memblock_alloc_try_nid(THREAD_SIZE, THREAD_ALIGN,
MEMBLOCK_LOW_LIMIT, limit,
early_cpu_to_node(cpu));
if (!ptr)
diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 8834220036a5..b4c89a1acebb 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -323,7 +323,7 @@ SECTIONS
#endif

/* The initial task and kernel stack */
- INIT_TASK_DATA_SECTION(THREAD_SIZE)
+ INIT_TASK_DATA_SECTION(THREAD_ALIGN)

.data..page_aligned : AT(ADDR(.data..page_aligned) - LOAD_OFFSET) {
PAGE_ALIGNED_DATA(PAGE_SIZE)
--
2.13.3
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