[RFC PATCH 06/12] scs: place init shadow stack in .shadowstack section

[Deepak Gupta <debug@rivosinc.com>]

If compiled for riscv and dynamic scs is turned on, place shadow stack in
`.shadowstack` section. Arch specific linker script can place logic to
protect this section against regular stores.

Signed-off-by: Deepak Gupta <debug@rivosinc.com>
---
 include/linux/init_task.h |  5 +++++
 init/init_task.c          | 12 ++++++++++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index bccb3f1f6262..f025022e1164 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -40,4 +40,9 @@ extern struct cred init_cred;
 /* Attach to the thread_info data structure for proper alignment */
 #define __init_thread_info __section(".data..init_thread_info")
 
+#if defined(CONFIG_RISCV) && defined(CONFIG_DYNAMIC_SCS)
+/* init shadow stack page */
+#define __init_shadow_stack __section(".shadowstack..init")
+#endif
+
 #endif
diff --git a/init/init_task.c b/init/init_task.c
index 4daee6d761c8..3c0a01455978 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -52,10 +52,18 @@ static struct sighand_struct init_sighand = {
 };
 
 #ifdef CONFIG_SHADOW_CALL_STACK
-unsigned long init_shadow_call_stack[SCS_SIZE / sizeof(long)] = {
+unsigned long init_shadow_call_stack[SCS_SIZE / sizeof(long)]
+#if defined(CONFIG_RISCV) && defined(CONFIG_DYNAMIC_SCS)
+	/* RISC-V dynamic SCS implements shadow stack and must go in special section */
+	__init_shadow_stack = {
+	[0] = SCS_END_MAGIC
+};
+#else
+	= {
 	[(SCS_SIZE / sizeof(long)) - 1] = SCS_END_MAGIC
 };
-#endif
+#endif /* CONFIG_RISCV && CONFIG_DYNAMIC_SCS */
+#endif /* CONFIG_SHADOW_CALL_STACK */
 
 /*
  * Set up the first task table, touch at your own risk!. Base=0,
-- 
2.43.2