[PATCH v3 24/29] riscv/ptrace: riscv cfi status and state via ptrace and in core files

Deepak Gupta
2024-04-04T00:49:35Z

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 or disabling 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 <debug@rivosinc.com>
---
arch/riscv/include/uapi/asm/ptrace.h | 18 ++++++
arch/riscv/kernel/ptrace.c | 83 ++++++++++++++++++++++++++++
include/uapi/linux/elf.h | 1 +
3 files changed, 102 insertions(+)

diff --git a/arch/riscv/include/uapi/asm/ptrace.h b/arch/riscv/include/uapi/asm/ptrace.h
index a38268b19c3d..512be06a8661 100644
--- a/arch/riscv/include/uapi/asm/ptrace.h
+++ b/arch/riscv/include/uapi/asm/ptrace.h
@@ -127,6 +127,24 @@ struct __riscv_v_regset_state {
*/
#define RISCV_MAX_VLENB (8192)

+struct __cfi_status {
+ /* indirect branch tracking state */
+ __u64 lp_en : 1;
+ __u64 lp_lock : 1;
+ __u64 elp_state : 1;
+
+ /* shadow stack status */
+ __u64 shstk_en : 1;
+ __u64 shstk_lock : 1;
+
+ __u64 rsvd : sizeof(__u64) - 5;
+};
+
+struct user_cfi_state {
+ struct __cfi_status cfi_status;
+ __u64 shstk_ptr;
+};
+
#endif /* __ASSEMBLY__ */

#endif /* _UAPI_ASM_RISCV_PTRACE_H */
diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
index e8515aa9d80b..33d4b32cc6a7 100644
--- a/arch/riscv/kernel/ptrace.c
+++ b/arch/riscv/kernel/ptrace.c
@@ -19,6 +19,7 @@
#include <linux/regset.h>
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
+#include <asm/usercfi.h>

enum riscv_regset {
REGSET_X,
@@ -28,6 +29,9 @@ enum riscv_regset {
#ifdef CONFIG_RISCV_ISA_V
REGSET_V,
#endif
+#ifdef CONFIG_RISCV_USER_CFI
+ REGSET_CFI,
+#endif
};

static int riscv_gpr_get(struct task_struct *target,
@@ -152,6 +156,75 @@ static int riscv_vr_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;
+
+ regs = task_pt_regs(target);
+
+ user_cfi.cfi_status.lp_en = is_indir_lp_enabled(target);
+ user_cfi.cfi_status.lp_lock = is_indir_lp_locked(target);
+ user_cfi.cfi_status.elp_state = (regs->status & SR_ELP);
+
+ user_cfi.cfi_status.shstk_en = is_shstk_enabled(target);
+ user_cfi.cfi_status.shstk_lock = is_shstk_locked(target);
+ 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.lp_en || user_cfi.cfi_status.lp_lock ||
+ user_cfi.cfi_status.shstk_en || user_cfi.cfi_status.shstk_lock ||
+ !user_cfi.cfi_status.rsvd)
+ 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.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))
+ set_active_shstk(target, user_cfi.shstk_ptr);
+
+ return 0;
+}
+#endif
+
static const struct user_regset riscv_user_regset[] = {
[REGSET_X] = {
.core_note_type = NT_PRSTATUS,
@@ -182,6 +255,16 @@ static const struct user_regset riscv_user_regset[] = {
.set = riscv_vr_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 9417309b7230..f60b2de66b1c 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -447,6 +447,7 @@ typedef struct elf64_shdr {
#define NT_MIPS_MSA 0x802 /* MIPS SIMD registers */
#define NT_RISCV_CSR 0x900 /* RISC-V Control and Status Registers */
#define NT_RISCV_VECTOR 0x901 /* RISC-V vector registers */
+#define NT_RISCV_USER_CFI 0x902 /* RISC-V shadow stack state */
#define NT_LOONGARCH_CPUCFG 0xa00 /* LoongArch CPU config registers */
#define NT_LOONGARCH_CSR 0xa01 /* LoongArch control and status registers */
#define NT_LOONGARCH_LSX 0xa02 /* LoongArch Loongson SIMD Extension registers */
--
2.43.2