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Thu, 04 Dec 2025 12:04:36 -0800 (PST) Received: from debug.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-11df76e2eefsm10417454c88.6.2025.12.04.12.04.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Dec 2025 12:04:36 -0800 (PST) From: Deepak Gupta Date: Thu, 04 Dec 2025 12:04:08 -0800 Subject: [PATCH v24 19/28] riscv/ptrace: riscv cfi status and state via ptrace and in core files 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: <20251204-v5_user_cfi_series-v24-19-ada7a3ba14dc@rivosinc.com> References: <20251204-v5_user_cfi_series-v24-0-ada7a3ba14dc@rivosinc.com> In-Reply-To: <20251204-v5_user_cfi_series-v24-0-ada7a3ba14dc@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, Valentin Haudiquet , Deepak Gupta X-Mailer: b4 0.13.0 X-Developer-Signature: v=1; a=ed25519-sha256; t=1764878636; l=6975; i=debug@rivosinc.com; s=20251023; h=from:subject:message-id; bh=10adw+B6s48GPS/UC8IWlsl2AVRKonZeAmtNEJH3LPo=; b=CMZQRWz2W8CrkddpWb9ozS+EDBkizyUuT/D23DUG5KA+ZTl0kvMohkWejR2AbP4Ckfzq8LmK6 vbl0smGVKKlDeejUnXC5Wfh1RECC3yaX9MC67oPNwQa+KLqt2UyMs49 X-Developer-Key: i=debug@rivosinc.com; a=ed25519; pk=O37GQv1thBhZToXyQKdecPDhtWVbEDRQ0RIndijvpjk= 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. Tested-by: Valentin Haudiquet 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 */ }; =20 +#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__ */ =20 #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 =20 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 }; =20 static int riscv_gpr_get(struct task_struct *target, @@ -184,6 +188,87 @@ static int tagged_addr_ctrl_set(struct task_struct *ta= rget, } #endif =20 +#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 =3D task_pt_regs(target); + + if (is_indir_lp_enabled(target)) { + user_cfi.cfi_status.cfi_state |=3D PTRACE_CFI_LP_EN_STATE; + user_cfi.cfi_status.cfi_state |=3D is_indir_lp_locked(target) ? + PTRACE_CFI_LP_LOCK_STATE : 0; + user_cfi.cfi_status.cfi_state |=3D (regs->status & SR_ELP) ? + PTRACE_CFI_ELP_STATE : 0; + } + + if (is_shstk_enabled(target)) { + user_cfi.cfi_status.cfi_state |=3D (PTRACE_CFI_SS_EN_STATE | + PTRACE_CFI_SS_PTR_STATE); + user_cfi.cfi_status.cfi_state |=3D is_shstk_locked(target) ? + PTRACE_CFI_SS_LOCK_STATE : 0; + user_cfi.shstk_ptr =3D 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 =3D task_pt_regs(target); + + ret =3D 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, d= o that */ + if (is_indir_lp_enabled(target)) { + if (user_cfi.cfi_status.cfi_state & + PTRACE_CFI_ELP_STATE) /* set elp state */ + regs->status |=3D SR_ELP; + else + regs->status &=3D ~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[] =3D { [REGSET_X] =3D { USER_REGSET_NOTE_TYPE(PRSTATUS), @@ -224,6 +309,16 @@ static const struct user_regset riscv_user_regset[] = =3D { .set =3D tagged_addr_ctrl_set, }, #endif +#ifdef CONFIG_RISCV_USER_CFI + [REGSET_CFI] =3D { + .core_note_type =3D NT_RISCV_USER_CFI, + .align =3D sizeof(__u64), + .n =3D sizeof(struct user_cfi_state) / sizeof(__u64), + .size =3D sizeof(__u64), + .regset_get =3D riscv_cfi_get, + .set =3D riscv_cfi_set, + }, +#endif }; =20 static const struct user_regset_view riscv_user_native_view =3D { 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" --=20 2.45.0