From: Deepak Gupta <debug@xxxxxxxxxxxx> Carves out space in arch specific thread struct for cfi status and shadow stack in usermode on riscv. This patch does following - defines a new structure cfi_status with status bit for cfi feature - defines shadow stack pointer, base and size in cfi_status structure - defines offsets to new member fields in thread in asm-offsets.c - Saves and restore shadow stack pointer on trap entry (U --> S) and exit (S --> U) Signed-off-by: Deepak Gupta <debug@xxxxxxxxxxxx> --- arch/riscv/include/asm/processor.h | 1 + arch/riscv/include/asm/thread_info.h | 3 +++ arch/riscv/include/asm/usercfi.h | 24 ++++++++++++++++++++++++ arch/riscv/kernel/asm-offsets.c | 5 ++++- arch/riscv/kernel/entry.S | 25 +++++++++++++++++++++++++ 5 files changed, 57 insertions(+), 1 deletion(-) create mode 100644 arch/riscv/include/asm/usercfi.h diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h index ee2f51787ff8..d4dc298880fc 100644 --- a/arch/riscv/include/asm/processor.h +++ b/arch/riscv/include/asm/processor.h @@ -14,6 +14,7 @@ #include <asm/ptrace.h> #include <asm/hwcap.h> +#include <asm/usercfi.h> #ifdef CONFIG_64BIT #define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h index 320bc899a63b..6a2acecec546 100644 --- a/arch/riscv/include/asm/thread_info.h +++ b/arch/riscv/include/asm/thread_info.h @@ -58,6 +58,9 @@ struct thread_info { int cpu; unsigned long syscall_work; /* SYSCALL_WORK_ flags */ unsigned long envcfg; +#ifdef CONFIG_RISCV_USER_CFI + struct cfi_status user_cfi_state; +#endif #ifdef CONFIG_SHADOW_CALL_STACK void *scs_base; void *scs_sp; diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/usercfi.h new file mode 100644 index 000000000000..080d7077d12c --- /dev/null +++ b/arch/riscv/include/asm/usercfi.h @@ -0,0 +1,24 @@ +/* SPDX-License-Identifier: GPL-2.0 + * Copyright (C) 2023 Rivos, Inc. + * Deepak Gupta <debug@xxxxxxxxxxxx> + */ +#ifndef _ASM_RISCV_USERCFI_H +#define _ASM_RISCV_USERCFI_H + +#ifndef __ASSEMBLY__ +#include <linux/types.h> + +#ifdef CONFIG_RISCV_USER_CFI +struct cfi_status { + unsigned long ubcfi_en : 1; /* Enable for backward cfi. */ + unsigned long rsvd : ((sizeof(unsigned long)*8) - 1); + unsigned long user_shdw_stk; /* Current user shadow stack pointer */ + unsigned long shdw_stk_base; /* Base address of shadow stack */ + unsigned long shdw_stk_size; /* size of shadow stack */ +}; + +#endif /* CONFIG_RISCV_USER_CFI */ + +#endif /* __ASSEMBLY__ */ + +#endif /* _ASM_RISCV_USERCFI_H */ diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c index cdd8f095c30c..5e1f412e96ba 100644 --- a/arch/riscv/kernel/asm-offsets.c +++ b/arch/riscv/kernel/asm-offsets.c @@ -43,8 +43,11 @@ void asm_offsets(void) #ifdef CONFIG_SHADOW_CALL_STACK OFFSET(TASK_TI_SCS_SP, task_struct, thread_info.scs_sp); #endif - OFFSET(TASK_TI_CPU_NUM, task_struct, thread_info.cpu); +#ifdef CONFIG_RISCV_USER_CFI + OFFSET(TASK_TI_CFI_STATUS, task_struct, thread_info.user_cfi_state); + OFFSET(TASK_TI_USER_SSP, task_struct, thread_info.user_cfi_state.user_shdw_stk); +#endif OFFSET(TASK_THREAD_F0, task_struct, thread.fstate.f[0]); OFFSET(TASK_THREAD_F1, task_struct, thread.fstate.f[1]); OFFSET(TASK_THREAD_F2, task_struct, thread.fstate.f[2]); diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S index 63c3855ba80d..410659e2eadb 100644 --- a/arch/riscv/kernel/entry.S +++ b/arch/riscv/kernel/entry.S @@ -49,6 +49,21 @@ SYM_CODE_START(handle_exception) REG_S x5, PT_T0(sp) save_from_x6_to_x31 +#ifdef CONFIG_RISCV_USER_CFI + /* + * we need to save cfi status only when previous mode was U + */ + csrr s2, CSR_STATUS + andi s2, s2, SR_SPP + bnez s2, skip_bcfi_save + /* load cfi status word */ + lw s3, TASK_TI_CFI_STATUS(tp) + andi s3, s3, 1 + beqz s3, skip_bcfi_save + csrr s3, CSR_SSP + REG_S s3, TASK_TI_USER_SSP(tp) /* save user ssp in thread_info */ +skip_bcfi_save: +#endif /* * Disable user-mode memory access as it should only be set in the * actual user copy routines. @@ -141,6 +156,16 @@ SYM_CODE_START_NOALIGN(ret_from_exception) * structures again. */ csrw CSR_SCRATCH, tp + +#ifdef CONFIG_RISCV_USER_CFI + lw s3, TASK_TI_CFI_STATUS(tp) + andi s3, s3, 1 + beqz s3, skip_bcfi_resume + REG_L s3, TASK_TI_USER_SSP(tp) /* restore user ssp from thread struct */ + csrw CSR_SSP, s3 +skip_bcfi_resume: +#endif + 1: REG_L a0, PT_STATUS(sp) /* -- 2.43.0