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Wed, 15 Oct 2025 11:14:26 -0700 (PDT) From: Deepak Gupta Date: Wed, 15 Oct 2025 11:13:51 -0700 Subject: [PATCH v21 19/28] riscv/ptrace: riscv cfi status and state via ptrace and in core files MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20251015-v5_user_cfi_series-v21-19-6a07856e90e7@rivosinc.com> References: <20251015-v5_user_cfi_series-v21-0-6a07856e90e7@rivosinc.com> In-Reply-To: <20251015-v5_user_cfi_series-v21-0-6a07856e90e7@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, Deepak Gupta X-Mailer: b4 0.13.0 X-Rspamd-Queue-Id: 7C79840010 X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: 9uprfdfz4aucbgiay1b7nc5cwsbebcgt X-HE-Tag: 1760552068-462992 X-HE-Meta: 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 J+bsmFBl Mo7wiuiLDH3TB2Bh+qMMc/hrwmJz9ZGa+ZVT0pBGnsM6mQ98Tac9eVwPumrp1vFmsbsIuHOIGm3SxETsI8SS10rb42jqMpMFxta4ZV/z5cAlv6hWWCJLCyynKrO+rmR7hHVklkDtM2XGBCOyAuMwZ5EuUXZzfK0s0LAY53qCy8kqFb3kLHwDvoaalft00uJCAKAH3w7BKYfj1IwWhRtucwuQ+xbV2NtR5AYXANUHASh9CKRr/IMWgnp5D2kJTxYDYTHtD2OAJtCtWx4WC2kIxFI/nlKnjrUcSOooV8FyIFvn9CN7KmbPv+5JJVRXezDfnziZbygRo94btqC+vbFGB9mpkdHqOY+7ueP25RV78NL2pNjLWG9gMr7OC/tFtdVECY1W6YaIz+ZndPRDK+eIYuph6/SVyJjcxqRAr 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: Expose a new register type NT_RISCV_USER_CFI for risc-v cfi status and state. Intentionally both landing pad and shadow stack status and state are rolled into cfi state. Creating two different NT_RISCV_USER_XXX would not be useful and wastage of a note type. Enabling, disabling and locking of feature is not allowed via ptrace set interface. However setting `elp` state or setting shadow stack pointer are allowed via ptrace set interface . It is expected `gdb` might have use to fixup `elp` state or `shadow stack` pointer. Signed-off-by: Deepak Gupta --- arch/riscv/include/uapi/asm/ptrace.h | 30 ++++++++++++ arch/riscv/kernel/ptrace.c | 95 ++++++++++++++++++++++++++++++++++++ include/uapi/linux/elf.h | 2 + 3 files changed, 127 insertions(+) diff --git a/arch/riscv/include/uapi/asm/ptrace.h b/arch/riscv/include/uapi/asm/ptrace.h index 261bfe70f60a..b2a18dfeb2fb 100644 --- a/arch/riscv/include/uapi/asm/ptrace.h +++ b/arch/riscv/include/uapi/asm/ptrace.h @@ -131,6 +131,36 @@ struct __sc_riscv_cfi_state { unsigned long ss_ptr; /* shadow stack pointer */ }; +#define PTRACE_CFI_LP_EN_BIT 0 +#define PTRACE_CFI_LP_LOCK_BIT 1 +#define PTRACE_CFI_ELP_BIT 2 +#define PTRACE_CFI_SS_EN_BIT 3 +#define PTRACE_CFI_SS_LOCK_BIT 4 +#define PTRACE_CFI_SS_PTR_BIT 5 + +#define PTRACE_CFI_LP_EN_STATE (1 << PTRACE_CFI_LP_EN_BIT) +#define PTRACE_CFI_LP_LOCK_STATE (1 << PTRACE_CFI_LP_LOCK_BIT) +#define PTRACE_CFI_ELP_STATE (1 << PTRACE_CFI_ELP_BIT) +#define PTRACE_CFI_SS_EN_STATE (1 << PTRACE_CFI_SS_EN_BIT) +#define PTRACE_CFI_SS_LOCK_STATE (1 << PTRACE_CFI_SS_LOCK_BIT) +#define PTRACE_CFI_SS_PTR_STATE (1 << PTRACE_CFI_SS_PTR_BIT) + +#define PRACE_CFI_STATE_INVALID_MASK ~(PTRACE_CFI_LP_EN_STATE | \ + PTRACE_CFI_LP_LOCK_STATE | \ + PTRACE_CFI_ELP_STATE | \ + PTRACE_CFI_SS_EN_STATE | \ + PTRACE_CFI_SS_LOCK_STATE | \ + PTRACE_CFI_SS_PTR_STATE) + +struct __cfi_status { + __u64 cfi_state; +}; + +struct user_cfi_state { + struct __cfi_status cfi_status; + __u64 shstk_ptr; +}; + #endif /* __ASSEMBLER__ */ #endif /* _UAPI_ASM_RISCV_PTRACE_H */ diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c index 8e86305831ea..56b9e3871862 100644 --- a/arch/riscv/kernel/ptrace.c +++ b/arch/riscv/kernel/ptrace.c @@ -19,6 +19,7 @@ #include #include #include +#include enum riscv_regset { REGSET_X, @@ -31,6 +32,9 @@ enum riscv_regset { #ifdef CONFIG_RISCV_ISA_SUPM REGSET_TAGGED_ADDR_CTRL, #endif +#ifdef CONFIG_RISCV_USER_CFI + REGSET_CFI, +#endif }; static int riscv_gpr_get(struct task_struct *target, @@ -184,6 +188,87 @@ static int tagged_addr_ctrl_set(struct task_struct *target, } #endif +#ifdef CONFIG_RISCV_USER_CFI +static int riscv_cfi_get(struct task_struct *target, + const struct user_regset *regset, + struct membuf to) +{ + struct user_cfi_state user_cfi; + struct pt_regs *regs; + + memset(&user_cfi, 0, sizeof(user_cfi)); + regs = task_pt_regs(target); + + if (is_indir_lp_enabled(target)) { + user_cfi.cfi_status.cfi_state |= PTRACE_CFI_LP_EN_STATE; + user_cfi.cfi_status.cfi_state |= is_indir_lp_locked(target) ? + PTRACE_CFI_LP_LOCK_STATE : 0; + user_cfi.cfi_status.cfi_state |= (regs->status & SR_ELP) ? + PTRACE_CFI_ELP_STATE : 0; + } + + if (is_shstk_enabled(target)) { + user_cfi.cfi_status.cfi_state |= (PTRACE_CFI_SS_EN_STATE | + PTRACE_CFI_SS_PTR_STATE); + user_cfi.cfi_status.cfi_state |= is_shstk_locked(target) ? + PTRACE_CFI_SS_LOCK_STATE : 0; + user_cfi.shstk_ptr = get_active_shstk(target); + } + + return membuf_write(&to, &user_cfi, sizeof(user_cfi)); +} + +/* + * Does it make sense to allowing enable / disable of cfi via ptrace? + * Not allowing enable / disable / locking control via ptrace for now. + * Setting shadow stack pointer is allowed. GDB might use it to unwind or + * some other fixup. Similarly gdb might want to suppress elp and may want + * to reset elp state. + */ +static int riscv_cfi_set(struct task_struct *target, + const struct user_regset *regset, + unsigned int pos, unsigned int count, + const void *kbuf, const void __user *ubuf) +{ + int ret; + struct user_cfi_state user_cfi; + struct pt_regs *regs; + + regs = task_pt_regs(target); + + ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &user_cfi, 0, -1); + if (ret) + return ret; + + /* + * Not allowing enabling or locking shadow stack or landing pad + * There is no disabling of shadow stack or landing pad via ptrace + * rsvd field should be set to zero so that if those fields are needed in future + */ + if ((user_cfi.cfi_status.cfi_state & + (PTRACE_CFI_LP_EN_STATE | PTRACE_CFI_LP_LOCK_STATE | + PTRACE_CFI_SS_EN_STATE | PTRACE_CFI_SS_LOCK_STATE)) || + (user_cfi.cfi_status.cfi_state & PRACE_CFI_STATE_INVALID_MASK)) + return -EINVAL; + + /* If lpad is enabled on target and ptrace requests to set / clear elp, do that */ + if (is_indir_lp_enabled(target)) { + if (user_cfi.cfi_status.cfi_state & + PTRACE_CFI_ELP_STATE) /* set elp state */ + regs->status |= SR_ELP; + else + regs->status &= ~SR_ELP; /* clear elp state */ + } + + /* If shadow stack enabled on target, set new shadow stack pointer */ + if (is_shstk_enabled(target) && + (user_cfi.cfi_status.cfi_state & PTRACE_CFI_SS_PTR_STATE)) + set_active_shstk(target, user_cfi.shstk_ptr); + + return 0; +} +#endif + static const struct user_regset riscv_user_regset[] = { [REGSET_X] = { USER_REGSET_NOTE_TYPE(PRSTATUS), @@ -224,6 +309,16 @@ static const struct user_regset riscv_user_regset[] = { .set = tagged_addr_ctrl_set, }, #endif +#ifdef CONFIG_RISCV_USER_CFI + [REGSET_CFI] = { + .core_note_type = NT_RISCV_USER_CFI, + .align = sizeof(__u64), + .n = sizeof(struct user_cfi_state) / sizeof(__u64), + .size = sizeof(__u64), + .regset_get = riscv_cfi_get, + .set = riscv_cfi_set, + }, +#endif }; static const struct user_regset_view riscv_user_native_view = { diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h index 819ded2d39de..ee30dcd80901 100644 --- a/include/uapi/linux/elf.h +++ b/include/uapi/linux/elf.h @@ -545,6 +545,8 @@ typedef struct elf64_shdr { #define NT_RISCV_VECTOR 0x901 /* RISC-V vector registers */ #define NN_RISCV_TAGGED_ADDR_CTRL "LINUX" #define NT_RISCV_TAGGED_ADDR_CTRL 0x902 /* RISC-V tagged address control (prctl()) */ +#define NN_RISCV_USER_CFI "LINUX" +#define NT_RISCV_USER_CFI 0x903 /* RISC-V shadow stack state */ #define NN_LOONGARCH_CPUCFG "LINUX" #define NT_LOONGARCH_CPUCFG 0xa00 /* LoongArch CPU config registers */ #define NN_LOONGARCH_CSR "LINUX" -- 2.43.0