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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 , =?ISO-8859-15?Q?Bj=F6rn_Roy_Baron?= , Andreas Hindborg , Alice Ryhl , Trevor Gross , Benno Lossin , 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 Subject: Re: [PATCH v23 21/28] riscv: kernel command line option to opt out of user cfi In-Reply-To: <20251112-v5_user_cfi_series-v23-21-b55691eacf4f@rivosinc.com> Message-ID: References: <20251112-v5_user_cfi_series-v23-0-b55691eacf4f@rivosinc.com> <20251112-v5_user_cfi_series-v23-21-b55691eacf4f@rivosinc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: C7D874000A X-Rspamd-Server: rspam07 X-Stat-Signature: iohrermp959cz7bp78e6yoickk9nxu9i X-Rspam-User: X-HE-Tag: 1763569480-863981 X-HE-Meta: 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 8hMqTkk1 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 12 Nov 2025, Deepak Gupta via B4 Relay wrote: > From: Deepak Gupta > > 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 I fixed the checkpatch warnings on this patch and cleaned up the patch description slightly; see below. - Paul From: Deepak Gupta Date: Wed, 12 Nov 2025 16:43:19 -0800 Subject: [PATCH v23 21/28] riscv: add kernel command line option to opt out of user cfi 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: Deepak Gupta Link: https://patch.msgid.link/20251112-v5_user_cfi_series-v23-21-b55691eacf4f@rivosinc.com [pjw@kernel.org: fixed warnings from checkpatch; cleaned up patch description] Signed-off-by: Paul Walmsley --- .../admin-guide/kernel-parameters.txt | 8 +++ arch/riscv/include/asm/usercfi.h | 9 +++ arch/riscv/kernel/cpufeature.c | 9 ++- arch/riscv/kernel/usercfi.c | 58 +++++++++++++++---- 4 files changed, 71 insertions(+), 13 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 6c42061ca20e..453127ef8746 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. + 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 ec4b8a53eb74..7495baae1e3c 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 __ASSEMBLER__ #include #include @@ -13,6 +17,8 @@ struct task_struct; struct kernel_clone_args; +extern unsigned long riscv_nousercfi; + #ifdef CONFIG_RISCV_USER_CFI struct cfi_state { unsigned long ubcfi_en : 1; /* Enable for backward cfi. */ @@ -83,6 +89,9 @@ 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 /* __ASSEMBLER__ */ #endif /* _ASM_RISCV_USERCFI_H */ diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c index 106f6bcde5c8..b220fec9a239 100644 --- a/arch/riscv/kernel/cpufeature.c +++ b/arch/riscv/kernel/cpufeature.c @@ -28,6 +28,7 @@ #include #include #include +#include #define NUM_ALPHA_EXTS ('z' - 'a' + 1) @@ -45,6 +46,8 @@ struct riscv_isainfo hart_isa[NR_CPUS]; u32 thead_vlenb_of; +unsigned long riscv_nousercfi; + /** * riscv_isa_extension_base() - Get base extension word * @@ -277,7 +280,8 @@ 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; return 0; @@ -286,7 +290,8 @@ 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; return 0; diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c index 33c955d56eb3..d7a973c58943 100644 --- a/arch/riscv/kernel/usercfi.c +++ b/arch/riscv/kernel/usercfi.c @@ -17,6 +17,8 @@ #include #include +unsigned long 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 +508,37 @@ 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); -- 2.48.1