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Fri, 11 Jul 2025 12:46:53 -0700 (PDT) From: Deepak Gupta Date: Fri, 11 Jul 2025 12:46:18 -0700 Subject: [PATCH v18 13/27] prctl: arch-agnostic prctl for indirect branch tracking Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20250711-v5_user_cfi_series-v18-13-a8ee62f9f38e@rivosinc.com> References: <20250711-v5_user_cfi_series-v18-0-a8ee62f9f38e@rivosinc.com> In-Reply-To: <20250711-v5_user_cfi_series-v18-0-a8ee62f9f38e@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, Zong Li , Deepak Gupta X-Mailer: b4 0.13.0 Three architectures (x86, aarch64, riscv) have support for indirect branch tracking feature in a very similar fashion. On a very high level, indirect branch tracking is a CPU feature where CPU tracks branches which uses memory operand to perform control transfer in program. As part of this tracking on indirect branches, CPU goes in a state where it expects a landing pad instr on target and if not found then CPU raises some fault (architecture dependent) x86 landing pad instr - `ENDBRANCH` arch64 landing pad instr - `BTI` riscv landing instr - `lpad` Given that three major arches have support for indirect branch tracking, This patch makes `prctl` for indirect branch tracking arch agnostic. To allow userspace to enable this feature for itself, following prtcls are defined: - PR_GET_INDIR_BR_LP_STATUS: Gets current configured status for indirect branch tracking. - PR_SET_INDIR_BR_LP_STATUS: Sets a configuration for indirect branch tracking. Following status options are allowed - PR_INDIR_BR_LP_ENABLE: Enables indirect branch tracking on user thread. - PR_INDIR_BR_LP_DISABLE; Disables indirect branch tracking on user thread. - PR_LOCK_INDIR_BR_LP_STATUS: Locks configured status for indirect branch tracking for user thread. Reviewed-by: Mark Brown Reviewed-by: Zong Li Signed-off-by: Deepak Gupta --- include/linux/cpu.h | 4 ++++ include/uapi/linux/prctl.h | 27 +++++++++++++++++++++++++++ kernel/sys.c | 30 ++++++++++++++++++++++++++++++ 3 files changed, 61 insertions(+) diff --git a/include/linux/cpu.h b/include/linux/cpu.h index e6089abc28e2..e94cd69825e2 100644 --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -208,4 +208,8 @@ static inline bool cpu_mitigations_auto_nosmt(void) } #endif +int arch_get_indir_br_lp_status(struct task_struct *t, unsigned long __user *status); +int arch_set_indir_br_lp_status(struct task_struct *t, unsigned long status); +int arch_lock_indir_br_lp_status(struct task_struct *t, unsigned long status); + #endif /* _LINUX_CPU_H_ */ diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index 43dec6eed559..9cbb37afccda 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -371,4 +371,31 @@ struct prctl_mm_map { # define PR_FUTEX_HASH_GET_SLOTS 2 # define PR_FUTEX_HASH_GET_IMMUTABLE 3 +/* + * Get the current indirect branch tracking configuration for the current + * thread, this will be the value configured via PR_SET_INDIR_BR_LP_STATUS. + */ +#define PR_GET_INDIR_BR_LP_STATUS 79 + +/* + * Set the indirect branch tracking configuration. PR_INDIR_BR_LP_ENABLE will + * enable cpu feature for user thread, to track all indirect branches and ensure + * they land on arch defined landing pad instruction. + * x86 - If enabled, an indirect branch must land on `ENDBRANCH` instruction. + * arch64 - If enabled, an indirect branch must land on `BTI` instruction. + * riscv - If enabled, an indirect branch must land on `lpad` instruction. + * PR_INDIR_BR_LP_DISABLE will disable feature for user thread and indirect + * branches will no more be tracked by cpu to land on arch defined landing pad + * instruction. + */ +#define PR_SET_INDIR_BR_LP_STATUS 80 +# define PR_INDIR_BR_LP_ENABLE (1UL << 0) + +/* + * Prevent further changes to the specified indirect branch tracking + * configuration. All bits may be locked via this call, including + * undefined bits. + */ +#define PR_LOCK_INDIR_BR_LP_STATUS 81 + #endif /* _LINUX_PRCTL_H */ diff --git a/kernel/sys.c b/kernel/sys.c index adc0de0aa364..af6c28dc6b71 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2341,6 +2341,21 @@ int __weak arch_lock_shadow_stack_status(struct task_struct *t, unsigned long st return -EINVAL; } +int __weak arch_get_indir_br_lp_status(struct task_struct *t, unsigned long __user *status) +{ + return -EINVAL; +} + +int __weak arch_set_indir_br_lp_status(struct task_struct *t, unsigned long status) +{ + return -EINVAL; +} + +int __weak arch_lock_indir_br_lp_status(struct task_struct *t, unsigned long status) +{ + return -EINVAL; +} + #define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LOCAL_THROTTLE) #ifdef CONFIG_ANON_VMA_NAME @@ -2824,6 +2839,21 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, case PR_FUTEX_HASH: error = futex_hash_prctl(arg2, arg3, arg4); break; + case PR_GET_INDIR_BR_LP_STATUS: + if (arg3 || arg4 || arg5) + return -EINVAL; + error = arch_get_indir_br_lp_status(me, (unsigned long __user *)arg2); + break; + case PR_SET_INDIR_BR_LP_STATUS: + if (arg3 || arg4 || arg5) + return -EINVAL; + error = arch_set_indir_br_lp_status(me, arg2); + break; + case PR_LOCK_INDIR_BR_LP_STATUS: + if (arg3 || arg4 || arg5) + return -EINVAL; + error = arch_lock_indir_br_lp_status(me, arg2); + break; default: trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5); error = -EINVAL; -- 2.43.0