linux-kernel - [PATCH 07/11] scs: place init shadow stack in .shadowstack section

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Message-Id: <20250724-riscv_kcfi-v1-7-04b8fa44c98c@rivosinc.com>
Date: Thu, 24 Jul 2025 16:37:00 -0700
From: Deepak Gupta <debug@...osinc.com>
To: Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Alexandre Ghiti <alex@...ti.fr>, Masahiro Yamada <masahiroy@...nel.org>, 
 Nathan Chancellor <nathan@...nel.org>, 
 Nicolas Schier <nicolas.schier@...ux.dev>, 
 Andrew Morton <akpm@...ux-foundation.org>, 
 David Hildenbrand <david@...hat.com>, 
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, 
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
 Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, 
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, 
 Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
 Bill Wendling <morbo@...gle.com>, Monk Chiang <monk.chiang@...ive.com>, 
 Kito Cheng <kito.cheng@...ive.com>, Justin Stitt <justinstitt@...gle.com>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 linux-kbuild@...r.kernel.org, linux-mm@...ck.org, llvm@...ts.linux.dev, 
 rick.p.edgecombe@...el.com, broonie@...nel.org, cleger@...osinc.com, 
 samitolvanen@...gle.com, apatel@...tanamicro.com, ajones@...tanamicro.com, 
 conor.dooley@...rochip.com, charlie@...osinc.com, samuel.holland@...ive.com, 
 bjorn@...osinc.com, fweimer@...hat.com, jeffreyalaw@...il.com, 
 heinrich.schuchardt@...onical.com, andrew@...ive.com, ved@...osinc.com, 
 Deepak Gupta <debug@...osinc.com>
Subject: [PATCH 07/11] scs: place init shadow stack in .shadowstack section

If compiled scs and arch kernel shadow stack support, place shadow stack in
`.shadowstack` section.

Signed-off-by: Deepak Gupta <debug@...osinc.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..a2569cc5a7ff 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")

+#ifdef CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK
+/* 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 e557f622bd90..e21af9db5c09 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -54,10 +54,18 @@ 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)]
+#ifdef CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK
+	/* shadow stack must go in special section */
+	__init_shadow_stack = {
+	[0] = SCS_END_MAGIC
+};
+#else
+	= {
 	[(SCS_SIZE / sizeof(long)) - 1] = SCS_END_MAGIC
 };
-#endif
+#endif /* CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK */
+#endif /* CONFIG_SHADOW_CALL_STACK */

 /*
  * Set up the first task table, touch at your own risk!. Base=0,

-- 
2.43.0