[PATCH v15 21/27] riscv: kernel command line option to opt out of user cfi
Deepak Gupta
debug at rivosinc.com
Fri May 2 16:30:52 PDT 2025
This commit adds a kernel command line option using which user cfi can be
disabled. User backward cfi and forward cfi can be enabled independently.
Kernel command line parameter "riscv_nousercfi" can take below values:
- "all" : Disable forward and backward cfi both.
- "bcfi" : Disable backward cfi.
- "fcfi" : Disable forward cfi
Signed-off-by: Deepak Gupta <debug at rivosinc.com>
---
Documentation/admin-guide/kernel-parameters.txt | 8 ++++
arch/riscv/include/asm/usercfi.h | 7 +++
arch/riscv/kernel/usercfi.c | 59 ++++++++++++++++++++-----
3 files changed, 63 insertions(+), 11 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 76e538c77e31..f75d50420a56 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6237,6 +6237,14 @@
replacement properties are not found. See the Kconfig
entry for RISCV_ISA_FALLBACK.
+ riscv_nousercfi=
+ all Disable user cfi ABI to userspace even if cpu extension
+ are available.
+ bcfi Disable user backward cfi ABI to userspace even if
+ shadow stack extension is available.
+ fcfi Disable user forward cfi ABI to userspace even if landing
+ pad extension is available.
+
ro [KNL] Mount root device read-only on boot
rodata= [KNL,EARLY]
diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/usercfi.h
index 68da5b7b79fd..6867ba6bd5a5 100644
--- a/arch/riscv/include/asm/usercfi.h
+++ b/arch/riscv/include/asm/usercfi.h
@@ -5,6 +5,10 @@
#ifndef _ASM_RISCV_USERCFI_H
#define _ASM_RISCV_USERCFI_H
+#define CMDLINE_DISABLE_RISCV_USERCFI_FCFI 1
+#define CMDLINE_DISABLE_RISCV_USERCFI_BCFI 2
+#define CMDLINE_DISABLE_RISCV_USERCFI 3
+
#ifndef __ASSEMBLY__
#include <linux/types.h>
#include <linux/prctl.h>
@@ -83,6 +87,9 @@ void set_indir_lp_lock(struct task_struct *task);
#endif /* CONFIG_RISCV_USER_CFI */
+bool is_user_shstk_enabled(void);
+bool is_user_lpad_enabled(void);
+
#endif /* __ASSEMBLY__ */
#endif /* _ASM_RISCV_USERCFI_H */
diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c
index 8bc3e1e3f712..5ef357f43ad7 100644
--- a/arch/riscv/kernel/usercfi.c
+++ b/arch/riscv/kernel/usercfi.c
@@ -17,6 +17,8 @@
#include <asm/csr.h>
#include <asm/usercfi.h>
+unsigned int riscv_nousercfi;
+
#define SHSTK_ENTRY_SIZE sizeof(void *)
bool is_shstk_enabled(struct task_struct *task)
@@ -59,7 +61,7 @@ unsigned long get_active_shstk(struct task_struct *task)
void set_shstk_status(struct task_struct *task, bool enable)
{
- if (!cpu_supports_shadow_stack())
+ if (!is_user_shstk_enabled())
return;
task->thread_info.user_cfi_state.ubcfi_en = enable ? 1 : 0;
@@ -89,7 +91,7 @@ bool is_indir_lp_locked(struct task_struct *task)
void set_indir_lp_status(struct task_struct *task, bool enable)
{
- if (!cpu_supports_indirect_br_lp_instr())
+ if (!is_user_lpad_enabled())
return;
task->thread_info.user_cfi_state.ufcfi_en = enable ? 1 : 0;
@@ -259,7 +261,7 @@ SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, unsigned long, size, unsi
bool set_tok = flags & SHADOW_STACK_SET_TOKEN;
unsigned long aligned_size = 0;
- if (!cpu_supports_shadow_stack())
+ if (!is_user_shstk_enabled())
return -EOPNOTSUPP;
/* Anything other than set token should result in invalid param */
@@ -306,7 +308,7 @@ unsigned long shstk_alloc_thread_stack(struct task_struct *tsk,
unsigned long addr, size;
/* If shadow stack is not supported, return 0 */
- if (!cpu_supports_shadow_stack())
+ if (!is_user_shstk_enabled())
return 0;
/*
@@ -352,7 +354,7 @@ void shstk_release(struct task_struct *tsk)
{
unsigned long base = 0, size = 0;
/* If shadow stack is not supported or not enabled, nothing to release */
- if (!cpu_supports_shadow_stack() || !is_shstk_enabled(tsk))
+ if (!is_user_shstk_enabled() || !is_shstk_enabled(tsk))
return;
/*
@@ -381,7 +383,7 @@ int arch_get_shadow_stack_status(struct task_struct *t, unsigned long __user *st
{
unsigned long bcfi_status = 0;
- if (!cpu_supports_shadow_stack())
+ if (!is_user_shstk_enabled())
return -EINVAL;
/* this means shadow stack is enabled on the task */
@@ -395,7 +397,7 @@ int arch_set_shadow_stack_status(struct task_struct *t, unsigned long status)
unsigned long size = 0, addr = 0;
bool enable_shstk = false;
- if (!cpu_supports_shadow_stack())
+ if (!is_user_shstk_enabled())
return -EINVAL;
/* Reject unknown flags */
@@ -448,7 +450,7 @@ int arch_lock_shadow_stack_status(struct task_struct *task,
unsigned long arg)
{
/* If shtstk not supported or not enabled on task, nothing to lock here */
- if (!cpu_supports_shadow_stack() ||
+ if (!is_user_shstk_enabled() ||
!is_shstk_enabled(task) || arg != 0)
return -EINVAL;
@@ -461,7 +463,7 @@ int arch_get_indir_br_lp_status(struct task_struct *t, unsigned long __user *sta
{
unsigned long fcfi_status = 0;
- if (!cpu_supports_indirect_br_lp_instr())
+ if (!is_user_lpad_enabled())
return -EINVAL;
/* indirect branch tracking is enabled on the task or not */
@@ -474,7 +476,7 @@ int arch_set_indir_br_lp_status(struct task_struct *t, unsigned long status)
{
bool enable_indir_lp = false;
- if (!cpu_supports_indirect_br_lp_instr())
+ if (!is_user_lpad_enabled())
return -EINVAL;
/* indirect branch tracking is locked and further can't be modified by user */
@@ -498,7 +500,7 @@ int arch_lock_indir_br_lp_status(struct task_struct *task,
* If indirect branch tracking is not supported or not enabled on task,
* nothing to lock here
*/
- if (!cpu_supports_indirect_br_lp_instr() ||
+ if (!is_user_lpad_enabled() ||
!is_indir_lp_enabled(task) || arg != 0)
return -EINVAL;
@@ -506,3 +508,38 @@ int arch_lock_indir_br_lp_status(struct task_struct *task,
return 0;
}
+
+bool is_user_shstk_enabled(void)
+{
+ return (cpu_supports_shadow_stack() &&
+ !(riscv_nousercfi & CMDLINE_DISABLE_RISCV_USERCFI_BCFI));
+}
+
+bool is_user_lpad_enabled(void)
+{
+ return (cpu_supports_indirect_br_lp_instr() &&
+ !(riscv_nousercfi & CMDLINE_DISABLE_RISCV_USERCFI_FCFI));
+}
+
+static int __init setup_global_riscv_enable(char *str)
+{
+ if (strcmp(str, "all") == 0)
+ riscv_nousercfi = CMDLINE_DISABLE_RISCV_USERCFI;
+
+ if (strcmp(str, "fcfi") == 0)
+ riscv_nousercfi |= CMDLINE_DISABLE_RISCV_USERCFI_FCFI;
+
+ if (strcmp(str, "bcfi") == 0)
+ riscv_nousercfi |= CMDLINE_DISABLE_RISCV_USERCFI_BCFI;
+
+ if (riscv_nousercfi)
+ pr_info("riscv user cfi disabled via cmdline"
+ "shadow stack status : %s, landing pad status : %s\n",
+ (riscv_nousercfi & CMDLINE_DISABLE_RISCV_USERCFI_BCFI) ? "disabled" :
+ "enabled", (riscv_nousercfi & CMDLINE_DISABLE_RISCV_USERCFI_FCFI) ?
+ "disabled" : "enabled");
+
+ return 1;
+}
+
+__setup("riscv_nousercfi=", setup_global_riscv_enable);
--
2.43.0
More information about the linux-riscv
mailing list