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Fri, 05 Dec 2025 10:37:30 -0800 (PST) Received: from debug.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2aba8395d99sm23933342eec.1.2025.12.05.10.37.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Dec 2025 10:37:30 -0800 (PST) From: Deepak Gupta Date: Fri, 05 Dec 2025 10:37:07 -0800 Subject: [PATCH v25 21/28] riscv: kernel command line option to opt out of user cfi Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20251205-v5_user_cfi_series-v25-21-8a3570c3e145@rivosinc.com> References: <20251205-v5_user_cfi_series-v25-0-8a3570c3e145@rivosinc.com> In-Reply-To: <20251205-v5_user_cfi_series-v25-0-8a3570c3e145@rivosinc.com> To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Lorenzo Stoakes , Paul Walmsley , Palmer Dabbelt , Albert Ou , Conor Dooley , Rob Herring , Krzysztof Kozlowski , Arnd Bergmann , Christian Brauner , Peter Zijlstra , Oleg Nesterov , Eric Biederman , Kees Cook , Jonathan Corbet , Shuah Khan , Jann Horn , Conor Dooley , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= , Andreas Hindborg , Alice Ryhl , Trevor Gross , Benno Lossin Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, alistair.francis@wdc.com, richard.henderson@linaro.org, jim.shu@sifive.com, andybnac@gmail.com, kito.cheng@sifive.com, charlie@rivosinc.com, atishp@rivosinc.com, evan@rivosinc.com, cleger@rivosinc.com, alexghiti@rivosinc.com, samitolvanen@google.com, broonie@kernel.org, rick.p.edgecombe@intel.com, rust-for-linux@vger.kernel.org, Paul Walmsley , Valentin Haudiquet , Deepak Gupta X-Mailer: b4 0.13.0 X-Developer-Signature: v=1; a=ed25519-sha256; t=1764959808; l=8783; i=debug@rivosinc.com; s=20251023; h=from:subject:message-id; bh=s7aGrFdVNwwtkxcsJPpFVS+aOTes7FH9SYpSNwarzgE=; b=m/Gqbo+50xmCBVFhWkamN3oTwOFuohPMg61Uh32kauHlEdUzHUvSIWPOUnhy6ADpZ0VjLaNrm a2t7DdOS17lA9NTo0Ck3sbSQSWIclrIDlQw3HlOH4vAtvLIUycoGCtx X-Developer-Key: i=debug@rivosinc.com; a=ed25519; pk=O37GQv1thBhZToXyQKdecPDhtWVbEDRQ0RIndijvpjk= This commit adds a kernel command line option to disable part or all of user cfi. User backward cfi and forward cfi can be controlled independently. Kernel command line parameter "riscv_nousercfi" can take the following values: - "all" : Disable forward and backward cfi both. - "bcfi" : Disable backward cfi. - "fcfi" : Disable forward cfi Signed-off-by: Paul Walmsley Tested-by: Valentin Haudiquet Signed-off-by: Deepak Gupta --- Documentation/admin-guide/kernel-parameters.txt | 8 ++++ arch/riscv/include/asm/usercfi.h | 9 ++++ arch/riscv/kernel/cpufeature.c | 7 ++- arch/riscv/kernel/usercfi.c | 59 ++++++++++++++++++++-= ---- 4 files changed, 70 insertions(+), 13 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentatio= n/admin-guide/kernel-parameters.txt index 6c42061ca20e..a72bf9fc6f06 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -6453,6 +6453,14 @@ replacement properties are not found. See the Kconfig entry for RISCV_ISA_FALLBACK. =20 + riscv_nousercfi=3D + all Disable user cfi ABI to userspace even if cpu extensions + 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 =20 rodata=3D [KNL,EARLY] diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/user= cfi.h index ec4b8a53eb74..f7fa9d602aae 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 =20 +#define CMDLINE_DISABLE_RISCV_USERCFI_FCFI 1 +#define CMDLINE_DISABLE_RISCV_USERCFI_BCFI 2 +#define CMDLINE_DISABLE_RISCV_USERCFI 3 + #ifndef __ASSEMBLER__ #include #include @@ -12,8 +16,10 @@ =20 struct task_struct; struct kernel_clone_args; +extern unsigned long riscv_nousercfi; =20 #ifdef CONFIG_RISCV_USER_CFI + struct cfi_state { unsigned long ubcfi_en : 1; /* Enable for backward cfi. */ unsigned long ubcfi_locked : 1; @@ -83,6 +89,9 @@ void set_indir_lp_lock(struct task_struct *task); =20 #endif /* CONFIG_RISCV_USER_CFI */ =20 +bool is_user_shstk_enabled(void); +bool is_user_lpad_enabled(void); + #endif /* __ASSEMBLER__ */ =20 #endif /* _ASM_RISCV_USERCFI_H */ diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c index 17b9e77bafc3..32ad463545fa 100644 --- a/arch/riscv/kernel/cpufeature.c +++ b/arch/riscv/kernel/cpufeature.c @@ -28,6 +28,7 @@ #include #include #include +#include =20 #define NUM_ALPHA_EXTS ('z' - 'a' + 1) =20 @@ -277,7 +278,8 @@ static int riscv_ext_svadu_validate(const struct riscv_= isa_ext_data *data, static int riscv_cfilp_validate(const struct riscv_isa_ext_data *data, const unsigned long *isa_bitmap) { - if (!IS_ENABLED(CONFIG_RISCV_USER_CFI)) + if (!IS_ENABLED(CONFIG_RISCV_USER_CFI) || + (riscv_nousercfi & CMDLINE_DISABLE_RISCV_USERCFI_FCFI)) return -EINVAL; =20 return 0; @@ -286,7 +288,8 @@ static int riscv_cfilp_validate(const struct riscv_isa_= ext_data *data, static int riscv_cfiss_validate(const struct riscv_isa_ext_data *data, const unsigned long *isa_bitmap) { - if (!IS_ENABLED(CONFIG_RISCV_USER_CFI)) + if (!IS_ENABLED(CONFIG_RISCV_USER_CFI) || + (riscv_nousercfi & CMDLINE_DISABLE_RISCV_USERCFI_BCFI)) return -EINVAL; =20 return 0; diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c index 7f01befabd11..27b36034ea85 100644 --- a/arch/riscv/kernel/usercfi.c +++ b/arch/riscv/kernel/usercfi.c @@ -17,6 +17,8 @@ #include #include =20 +unsigned long riscv_nousercfi; + #define SHSTK_ENTRY_SIZE sizeof(void *) =20 bool is_shstk_enabled(struct task_struct *task) @@ -59,7 +61,7 @@ unsigned long get_active_shstk(struct task_struct *task) =20 void set_shstk_status(struct task_struct *task, bool enable) { - if (!cpu_supports_shadow_stack()) + if (!is_user_shstk_enabled()) return; =20 task->thread_info.user_cfi_state.ubcfi_en =3D enable ? 1 : 0; @@ -89,7 +91,7 @@ bool is_indir_lp_locked(struct task_struct *task) =20 void set_indir_lp_status(struct task_struct *task, bool enable) { - if (!cpu_supports_indirect_br_lp_instr()) + if (!is_user_lpad_enabled()) return; =20 task->thread_info.user_cfi_state.ufcfi_en =3D enable ? 1 : 0; @@ -259,7 +261,7 @@ SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, = unsigned long, size, unsi bool set_tok =3D flags & SHADOW_STACK_SET_TOKEN; unsigned long aligned_size =3D 0; =20 - if (!cpu_supports_shadow_stack()) + if (!is_user_shstk_enabled()) return -EOPNOTSUPP; =20 /* Anything other than set token should result in invalid param */ @@ -306,7 +308,7 @@ unsigned long shstk_alloc_thread_stack(struct task_stru= ct *tsk, unsigned long addr, size; =20 /* If shadow stack is not supported, return 0 */ - if (!cpu_supports_shadow_stack()) + if (!is_user_shstk_enabled()) return 0; =20 /* @@ -352,7 +354,7 @@ void shstk_release(struct task_struct *tsk) { unsigned long base =3D 0, size =3D 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; =20 /* @@ -381,7 +383,7 @@ int arch_get_shadow_stack_status(struct task_struct *t,= unsigned long __user *st { unsigned long bcfi_status =3D 0; =20 - if (!cpu_supports_shadow_stack()) + if (!is_user_shstk_enabled()) return -EINVAL; =20 /* 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 =3D 0, addr =3D 0; bool enable_shstk =3D false; =20 - if (!cpu_supports_shadow_stack()) + if (!is_user_shstk_enabled()) return -EINVAL; =20 /* Reject unknown flags */ @@ -448,7 +450,7 @@ int arch_lock_shadow_stack_status(struct task_struct *t= ask, 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 !=3D 0) return -EINVAL; =20 @@ -461,7 +463,7 @@ int arch_get_indir_br_lp_status(struct task_struct *t, = unsigned long __user *sta { unsigned long fcfi_status =3D 0; =20 - if (!cpu_supports_indirect_br_lp_instr()) + if (!is_user_lpad_enabled()) return -EINVAL; =20 /* 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 =3D false; =20 - if (!cpu_supports_indirect_br_lp_instr()) + if (!is_user_lpad_enabled()) return -EINVAL; =20 /* indirect branch tracking is locked and further can't be modified by us= er */ @@ -498,7 +500,7 @@ int arch_lock_indir_br_lp_status(struct task_struct *ta= sk, * 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 !=3D 0) return -EINVAL; =20 @@ -506,3 +508,38 @@ int arch_lock_indir_br_lp_status(struct task_struct *t= ask, =20 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") =3D=3D 0) + riscv_nousercfi =3D CMDLINE_DISABLE_RISCV_USERCFI; + + if (strcmp(str, "fcfi") =3D=3D 0) + riscv_nousercfi |=3D CMDLINE_DISABLE_RISCV_USERCFI_FCFI; + + if (strcmp(str, "bcfi") =3D=3D 0) + riscv_nousercfi |=3D 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=3D", setup_global_riscv_enable); --=20 2.45.0