fork: allow arch-override of VMAP stack alignment
In some cases, an architecture might wish its stacks to be aligned to a
boundary larger than THREAD_SIZE. For example, using an alignment of
double THREAD_SIZE can allow for stack overflows smaller than
THREAD_SIZE to be detected by checking a single bit of the stack
pointer.
This patch allows architectures to override the alignment of VMAP'd
stacks, by defining THREAD_ALIGN. Where not defined, this defaults to
THREAD_SIZE, as is the case today.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: linux-kernel@vger.kernel.org
diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
index 250a276..905d769 100644
--- a/include/linux/thread_info.h
+++ b/include/linux/thread_info.h
@@ -38,6 +38,10 @@ enum {
#ifdef __KERNEL__
+#ifndef THREAD_ALIGN
+#define THREAD_ALIGN THREAD_SIZE
+#endif
+
#ifdef CONFIG_DEBUG_STACK_USAGE
# define THREADINFO_GFP (GFP_KERNEL_ACCOUNT | __GFP_NOTRACK | \
__GFP_ZERO)
diff --git a/kernel/fork.c b/kernel/fork.c
index 17921b0..f12882a 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -88,6 +88,7 @@
#include <linux/sysctl.h>
#include <linux/kcov.h>
#include <linux/livepatch.h>
+#include <linux/thread_info.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
@@ -217,7 +218,7 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
return s->addr;
}
- stack = __vmalloc_node_range(THREAD_SIZE, THREAD_SIZE,
+ stack = __vmalloc_node_range(THREAD_SIZE, THREAD_ALIGN,
VMALLOC_START, VMALLOC_END,
THREADINFO_GFP,
PAGE_KERNEL,
