diff mbox series

[v15,22/27] riscv: enable kernel access to shadow stack memory via FWFT sbi call

Message ID 20250502-v5_user_cfi_series-v15-22-914966471885@rivosinc.com
State New
Headers show
Series riscv control-flow integrity for usermode | expand

Commit Message

Deepak Gupta May 2, 2025, 11:30 p.m. UTC 
Kernel will have to perform shadow stack operations on user shadow stack.
Like during signal delivery and sigreturn, shadow stack token must be
created and validated respectively. Thus shadow stack access for kernel
must be enabled.

In future when kernel shadow stacks are enabled for linux kernel, it must
be enabled as early as possible for better coverage and prevent imbalance
between regular stack and shadow stack. After `relocate_enable_mmu` has
been done, this is as early as possible it can enabled.

Reviewed-by: Zong Li <zong.li@sifive.com>
Signed-off-by: Deepak Gupta <debug@rivosinc.com>
---
 arch/riscv/kernel/asm-offsets.c |  4 ++++
 arch/riscv/kernel/head.S        | 27 +++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)
diff mbox series

Patch

diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
index f33945432f8f..7ab41f01aa17 100644
--- a/arch/riscv/kernel/asm-offsets.c
+++ b/arch/riscv/kernel/asm-offsets.c
@@ -514,4 +514,8 @@  void asm_offsets(void)
 	DEFINE(FREGS_A6,	    offsetof(struct __arch_ftrace_regs, a6));
 	DEFINE(FREGS_A7,	    offsetof(struct __arch_ftrace_regs, a7));
 #endif
+	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_SET_FLAG_LOCK, SBI_FWFT_SET_FLAG_LOCK);
 }
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index 356d5397b2a2..7eae9a172351 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -15,6 +15,7 @@ 
 #include <asm/image.h>
 #include <asm/scs.h>
 #include <asm/xip_fixup.h>
+#include <asm/usercfi.h>
 #include "efi-header.S"
 
 __HEAD
@@ -164,6 +165,19 @@  secondary_start_sbi:
 	call relocate_enable_mmu
 #endif
 	call .Lsetup_trap_vector
+#if defined(CONFIG_RISCV_SBI) && defined(CONFIG_RISCV_USER_CFI)
+	li a7, SBI_EXT_FWFT
+	li a6, SBI_EXT_FWFT_SET
+	li a0, SBI_FWFT_SHADOW_STACK
+	li a1, 1 /* enable supervisor to access shadow stack access */
+	li a2, SBI_FWFT_SET_FLAG_LOCK
+	ecall
+	beqz a0, 1f
+	la a1, riscv_nousercfi
+	li a0, CMDLINE_DISABLE_RISCV_USERCFI_BCFI
+	REG_S a0, (a1)
+1:
+#endif
 	scs_load_current
 	call smp_callin
 #endif /* CONFIG_SMP */
@@ -320,6 +334,19 @@  SYM_CODE_START(_start_kernel)
 	la tp, init_task
 	la sp, init_thread_union + THREAD_SIZE
 	addi sp, sp, -PT_SIZE_ON_STACK
+#if defined(CONFIG_RISCV_SBI) && defined(CONFIG_RISCV_USER_CFI)
+	li a7, SBI_EXT_FWFT
+	li a6, SBI_EXT_FWFT_SET
+	li a0, SBI_FWFT_SHADOW_STACK
+	li a1, 1 /* enable supervisor to access shadow stack access */
+	li a2, SBI_FWFT_SET_FLAG_LOCK
+	ecall
+	beqz a0, 1f
+	la a1, riscv_nousercfi
+	li a0, CMDLINE_DISABLE_RISCV_USERCFI_BCFI
+	REG_S a0, (a1)
+1:
+#endif
 	scs_load_current
 
 #ifdef CONFIG_KASAN