[RFC PATCH 12/12] riscv: enable kernel shadow stack and landing pad enforcement

[Deepak Gupta <debug@rivosinc.com>]

This patch enables kernel shadow stack and landing pad enforcement by
invoking a SBI call. As of now it just issues a SBI_EXT_BASE and a hacked
up opensbi implementation sets the LPE/SSE bits in menvcfg

Eventually, we should have fwft [1] interface using which kernel should be
able to set this enforcement properly

[1] - https://lists.riscv.org/g/tech-prs/message/833

Signed-off-by: Deepak Gupta <debug@rivosinc.com>
---
 arch/riscv/kernel/head.S | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index bc248c137c90..1e5bc7b2ee75 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -164,6 +164,13 @@ secondary_start_sbi:
 	call relocate_enable_mmu
 #endif
 	call .Lsetup_trap_vector
+	/*
+	 * Temp hack to get menvcfg.SSE=1 and menvcfg.LPE=1 by invoking
+	 * SBI_EXT_BASE
+	 */
+	li a6, 0
+	li a7, 0x10
+	ecall
 	scs_load_current t0
 	lui t2, 0x1
 	tail smp_callin
@@ -313,6 +320,13 @@ SYM_CODE_START(_start_kernel)
 	la tp, init_task
 	la sp, init_thread_union + THREAD_SIZE
 	addi sp, sp, -PT_SIZE_ON_STACK
+	/*
+	 * Temp hack to get menvcfg.SSE=1 and menvcfg.LPE=1 by invoking
+	 * SBI_EXT_BASE
+	 */
+	li a6, 0
+	li a7, 0x10
+	ecall
 	scs_load_current t0
 
 #ifdef CONFIG_KASAN
-- 
2.43.2