On Thu, Jan 25, 2024, at 1:21 AM, debug@rivosinc.com wrote:
From: Deepak Gupta debug@rivosinc.com
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@rivosinc.com
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@rivosinc.com
- */
+#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
We shouldn't need any of this in the entry/exit code, at least as long as the kernel itself is not using Zicfiss. ssp can keep its value in the kernel and swap it on task switches. Our entry/exit code is rather short and I'd like to keep it that way.
-s
1: REG_L a0, PT_STATUS(sp) /* -- 2.43.0
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