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 | 23 +++++++++++++++++++++++ 2 files changed, 27 insertions(+)
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..d47876eca637 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 +165,17 @@ secondary_start_sbi: call relocate_enable_mmu #endif call .Lsetup_trap_vector + 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: scs_load_current call smp_callin #endif /* CONFIG_SMP */ @@ -320,6 +332,17 @@ SYM_CODE_START(_start_kernel) la tp, init_task la sp, init_thread_union + THREAD_SIZE addi sp, sp, -PT_SIZE_ON_STACK + 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: scs_load_current
#ifdef CONFIG_KASAN