linux-kernel - [PATCH 02/14] fork: allow arch-override of VMAP stack alignment

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Date:   Mon,  7 Aug 2017 19:35:53 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     ard.biesheuvel@...aro.org, catalin.marinas@....com,
        james.morse@....com, labbott@...hat.com,
        linux-kernel@...r.kernel.org, luto@...capital.net,
        mark.rutland@....com, matt@...eblueprint.co.uk,
        will.deacon@....com, kernel-hardening@...ts.openwall.com,
        keescook@...omium.org
Subject: [PATCH 02/14] 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@....com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: James Morse <james.morse@....com>
Cc: Laura Abbott <labbott@...hat.com>
Cc: Will Deacon <will.deacon@....com>
Cc: linux-kernel@...r.kernel.org
---
 kernel/fork.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 17921b0..696d692 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -217,7 +217,10 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
 		return s->addr;
 	}
 
-	stack = __vmalloc_node_range(THREAD_SIZE, THREAD_SIZE,
+#ifndef THREAD_ALIGN
+#define THREAD_ALIGN	THREAD_SIZE
+#endif
+	stack = __vmalloc_node_range(THREAD_SIZE, THREAD_ALIGN,
 				     VMALLOC_START, VMALLOC_END,
 				     THREADINFO_GFP,
 				     PAGE_KERNEL,
-- 
1.9.1