linux-kernel - [PATCH 05/11] riscv: enable landing pad enforcement

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Message-Id: <20250724-riscv_kcfi-v1-5-04b8fa44c98c@rivosinc.com>
Date: Thu, 24 Jul 2025 16:36:58 -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 05/11] riscv: enable landing pad enforcement

Enables landing pad enforcement by invoking a SBI FWFT call.

Signed-off-by: Deepak Gupta <debug@...osinc.com>
---
 arch/riscv/kernel/asm-offsets.c |  1 +
 arch/riscv/kernel/head.S        | 19 +++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
index e4d55126dc3e..e6a9fad86fae 100644
--- a/arch/riscv/kernel/asm-offsets.c
+++ b/arch/riscv/kernel/asm-offsets.c
@@ -536,6 +536,7 @@ void asm_offsets(void)
 	DEFINE(SBI_EXT_FWFT, SBI_EXT_FWFT);
 	DEFINE(SBI_EXT_FWFT_SET, SBI_EXT_FWFT_SET);
 	DEFINE(SBI_FWFT_SHADOW_STACK, SBI_FWFT_SHADOW_STACK);
+	DEFINE(SBI_FWFT_LANDING_PAD, SBI_FWFT_LANDING_PAD);
 	DEFINE(SBI_FWFT_SET_FLAG_LOCK, SBI_FWFT_SET_FLAG_LOCK);
 #endif
 }
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index 9c99c5ad6fe8..59af044bf85c 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -185,6 +185,16 @@ secondary_start_sbi:
 1:
 #endif
 	scs_load_current
+
+#if defined(CONFIG_RISCV_SBI) && defined(CONFIG_RISCV_KERNEL_CFI)
+	li a7, SBI_EXT_FWFT
+	li a6, SBI_EXT_FWFT_SET
+	li a0, SBI_FWFT_LANDING_PAD
+	li a1, 1 /* enable landing pad for supervisor */
+	li a2, SBI_FWFT_SET_FLAG_LOCK
+	ecall	/* check for error condition and take appropriate action */
+#endif
+
 	call smp_callin
 #endif /* CONFIG_SMP */

@@ -359,6 +369,15 @@ SYM_CODE_START(_start_kernel)
 #endif
 	scs_load_current

+#if defined(CONFIG_RISCV_SBI) && defined(CONFIG_RISCV_KERNEL_CFI)
+	li a7, SBI_EXT_FWFT
+	li a6, SBI_EXT_FWFT_SET
+	li a0, SBI_FWFT_LANDING_PAD
+	li a1, 1 /* enable landing pad for supervisor */
+	li a2, SBI_FWFT_SET_FLAG_LOCK
+	ecall	/* check for error condition and take appropriate action */
+#endif
+
 #ifdef CONFIG_KASAN
 	call kasan_early_init
 #endif

-- 
2.43.0