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Mon, 20 Oct 2025 13:23:09 -0700 (PDT) From: Deepak Gupta Date: Mon, 20 Oct 2025 13:22:43 -0700 Subject: [PATCH v22 14/28] riscv: Implements arch agnostic indirect branch tracking prctls MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20251020-v5_user_cfi_series-v22-14-66732256ad8f@rivosinc.com> References: <20251020-v5_user_cfi_series-v22-0-66732256ad8f@rivosinc.com> In-Reply-To: <20251020-v5_user_cfi_series-v22-0-66732256ad8f@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 X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 6D84E80002 X-Stat-Signature: et88pt4abj6b4j7p664dj3ritpq3cth8 X-Rspam-User: X-HE-Tag: 1760991791-492697 X-HE-Meta: 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 HZIt3tb1 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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: prctls implemented are: PR_SET_INDIR_BR_LP_STATUS, PR_GET_INDIR_BR_LP_STATUS and PR_LOCK_INDIR_BR_LP_STATUS Reviewed-by: Zong Li Signed-off-by: Deepak Gupta --- arch/riscv/include/asm/usercfi.h | 14 +++++++ arch/riscv/kernel/entry.S | 4 ++ arch/riscv/kernel/process.c | 5 +++ arch/riscv/kernel/usercfi.c | 79 ++++++++++++++++++++++++++++++++++++++++ 4 files changed, 102 insertions(+) diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/usercfi.h index d71093f414df..4501d741a609 100644 --- a/arch/riscv/include/asm/usercfi.h +++ b/arch/riscv/include/asm/usercfi.h @@ -16,6 +16,8 @@ struct kernel_clone_args; struct cfi_state { unsigned long ubcfi_en : 1; /* Enable for backward cfi. */ unsigned long ubcfi_locked : 1; + unsigned long ufcfi_en : 1; /* Enable for forward cfi. Note that ELP goes in sstatus */ + unsigned long ufcfi_locked : 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 */ @@ -32,6 +34,10 @@ bool is_shstk_locked(struct task_struct *task); bool is_shstk_allocated(struct task_struct *task); void set_shstk_lock(struct task_struct *task); void set_shstk_status(struct task_struct *task, bool enable); +bool is_indir_lp_enabled(struct task_struct *task); +bool is_indir_lp_locked(struct task_struct *task); +void set_indir_lp_status(struct task_struct *task, bool enable); +void set_indir_lp_lock(struct task_struct *task); #define PR_SHADOW_STACK_SUPPORTED_STATUS_MASK (PR_SHADOW_STACK_ENABLE) @@ -57,6 +63,14 @@ void set_shstk_status(struct task_struct *task, bool enable); #define set_shstk_status(task, enable) do {} while (0) +#define is_indir_lp_enabled(task) false + +#define is_indir_lp_locked(task) false + +#define set_indir_lp_status(task, enable) do {} while (0) + +#define set_indir_lp_lock(task) do {} while (0) + #endif /* CONFIG_RISCV_USER_CFI */ #endif /* __ASSEMBLER__ */ diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S index 8410850953d6..036a6ca7641f 100644 --- a/arch/riscv/kernel/entry.S +++ b/arch/riscv/kernel/entry.S @@ -174,6 +174,10 @@ SYM_CODE_START(handle_exception) * or vector in kernel space. */ li t0, SR_SUM | SR_FS_VS +#ifdef CONFIG_64BIT + li t1, SR_ELP + or t0, t0, t1 +#endif REG_L s0, TASK_TI_USER_SP(tp) csrrc s1, CSR_STATUS, t0 diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c index a137d3483646..49f527e3acfd 100644 --- a/arch/riscv/kernel/process.c +++ b/arch/riscv/kernel/process.c @@ -163,6 +163,11 @@ void start_thread(struct pt_regs *regs, unsigned long pc, set_shstk_status(current, false); set_shstk_base(current, 0, 0); set_active_shstk(current, 0); + /* + * disable indirect branch tracking on exec. + * libc will enable it later via prctl. + */ + set_indir_lp_status(current, false); #ifdef CONFIG_64BIT regs->status &= ~SR_UXL; diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c index 08620bdae696..2ebe789caa6b 100644 --- a/arch/riscv/kernel/usercfi.c +++ b/arch/riscv/kernel/usercfi.c @@ -72,6 +72,35 @@ void set_shstk_lock(struct task_struct *task) task->thread_info.user_cfi_state.ubcfi_locked = 1; } +bool is_indir_lp_enabled(struct task_struct *task) +{ + return task->thread_info.user_cfi_state.ufcfi_en; +} + +bool is_indir_lp_locked(struct task_struct *task) +{ + return task->thread_info.user_cfi_state.ufcfi_locked; +} + +void set_indir_lp_status(struct task_struct *task, bool enable) +{ + if (!cpu_supports_indirect_br_lp_instr()) + return; + + task->thread_info.user_cfi_state.ufcfi_en = enable ? 1 : 0; + + if (enable) + task->thread.envcfg |= ENVCFG_LPE; + else + task->thread.envcfg &= ~ENVCFG_LPE; + + csr_write(CSR_ENVCFG, task->thread.envcfg); +} + +void set_indir_lp_lock(struct task_struct *task) +{ + task->thread_info.user_cfi_state.ufcfi_locked = 1; +} /* * If size is 0, then to be compatible with regular stack we want it to be as big as * regular stack. Else PAGE_ALIGN it and return back @@ -371,3 +400,53 @@ int arch_lock_shadow_stack_status(struct task_struct *task, return 0; } + +int arch_get_indir_br_lp_status(struct task_struct *t, unsigned long __user *status) +{ + unsigned long fcfi_status = 0; + + if (!cpu_supports_indirect_br_lp_instr()) + return -EINVAL; + + /* indirect branch tracking is enabled on the task or not */ + fcfi_status |= (is_indir_lp_enabled(t) ? PR_INDIR_BR_LP_ENABLE : 0); + + return copy_to_user(status, &fcfi_status, sizeof(fcfi_status)) ? -EFAULT : 0; +} + +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()) + return -EINVAL; + + /* indirect branch tracking is locked and further can't be modified by user */ + if (is_indir_lp_locked(t)) + return -EINVAL; + + /* Reject unknown flags */ + if (status & ~PR_INDIR_BR_LP_ENABLE) + return -EINVAL; + + enable_indir_lp = (status & PR_INDIR_BR_LP_ENABLE); + set_indir_lp_status(t, enable_indir_lp); + + return 0; +} + +int arch_lock_indir_br_lp_status(struct task_struct *task, + unsigned long arg) +{ + /* + * If indirect branch tracking is not supported or not enabled on task, + * nothing to lock here + */ + if (!cpu_supports_indirect_br_lp_instr() || + !is_indir_lp_enabled(task) || arg != 0) + return -EINVAL; + + set_indir_lp_lock(task); + + return 0; +} -- 2.45.0