[PATCH v8 25/38] arm64/ptrace: Expose GCS via ptrace and core files

Mark Brown
2024-02-03T12:32:30Z

Provide a new register type NT_ARM_GCS reporting the current GCS mode
and pointer for EL0. Due to the interactions with allocation and
deallocation of Guarded Control Stacks we do not permit any changes to
the GCS mode via ptrace, only GCSPR_EL0 may be changed.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/include/uapi/asm/ptrace.h | 8 +++++
arch/arm64/kernel/ptrace.c | 59 ++++++++++++++++++++++++++++++++++++
include/uapi/linux/elf.h | 1 +
3 files changed, 68 insertions(+)

diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
index 7fa2f7036aa7..0f39ba4f3efd 100644
--- a/arch/arm64/include/uapi/asm/ptrace.h
+++ b/arch/arm64/include/uapi/asm/ptrace.h
@@ -324,6 +324,14 @@ struct user_za_header {
#define ZA_PT_SIZE(vq) \
(ZA_PT_ZA_OFFSET + ZA_PT_ZA_SIZE(vq))

+/* GCS state (NT_ARM_GCS) */
+
+struct user_gcs {
+ __u64 features_enabled;
+ __u64 features_locked;
+ __u64 gcspr_el0;
+};
+
#endif /* __ASSEMBLY__ */

#endif /* _UAPI__ASM_PTRACE_H */
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index dc6cf0e37194..c8dd489cfca8 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -34,6 +34,7 @@
#include <asm/cpufeature.h>
#include <asm/debug-monitors.h>
#include <asm/fpsimd.h>
+#include <asm/gcs.h>
#include <asm/mte.h>
#include <asm/pointer_auth.h>
#include <asm/stacktrace.h>
@@ -1411,6 +1412,51 @@ static int tagged_addr_ctrl_set(struct task_struct *target, const struct
}
#endif

+#ifdef CONFIG_ARM64_GCS
+static int gcs_get(struct task_struct *target,
+ const struct user_regset *regset,
+ struct membuf to)
+{
+ struct user_gcs user_gcs;
+
+ if (target == current)
+ gcs_preserve_current_state();
+
+ user_gcs.features_enabled = target->thread.gcs_el0_mode;
+ user_gcs.features_locked = target->thread.gcs_el0_locked;
+ user_gcs.gcspr_el0 = target->thread.gcspr_el0;
+
+ return membuf_write(&to, &user_gcs, sizeof(user_gcs));
+}
+
+static int gcs_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_gcs user_gcs;
+
+ ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf, &user_gcs, 0, -1);
+ if (ret)
+ return ret;
+
+ if (user_gcs.features_enabled & ~PR_SHADOW_STACK_SUPPORTED_STATUS_MASK)
+ return -EINVAL;
+
+ /* Do not allow enable via ptrace */
+ if ((user_gcs.features_enabled & PR_SHADOW_STACK_ENABLE) &&
+ !(target->thread.gcs_el0_mode & PR_SHADOW_STACK_ENABLE))
+ return -EBUSY;
+
+ target->thread.gcs_el0_mode = user_gcs.features_enabled;
+ target->thread.gcs_el0_locked = user_gcs.features_locked;
+ target->thread.gcspr_el0 = user_gcs.gcspr_el0;
+
+ return 0;
+}
+#endif
+
enum aarch64_regset {
REGSET_GPR,
REGSET_FPR,
@@ -1439,6 +1485,9 @@ enum aarch64_regset {
#ifdef CONFIG_ARM64_TAGGED_ADDR_ABI
REGSET_TAGGED_ADDR_CTRL,
#endif
+#ifdef CONFIG_ARM64_GCS
+ REGSET_GCS,
+#endif
};

static const struct user_regset aarch64_regsets[] = {
@@ -1589,6 +1638,16 @@ static const struct user_regset aarch64_regsets[] = {
.set = tagged_addr_ctrl_set,
},
#endif
+#ifdef CONFIG_ARM64_GCS
+ [REGSET_GCS] = {
+ .core_note_type = NT_ARM_GCS,
+ .n = sizeof(struct user_gcs) / sizeof(u64),
+ .size = sizeof(u64),
+ .align = sizeof(u64),
+ .regset_get = gcs_get,
+ .set = gcs_set,
+ },
+#endif
};

static const struct user_regset_view user_aarch64_view = {
diff --git a/include/uapi/linux/elf.h b/include/uapi/linux/elf.h
index 9417309b7230..436dfc359f61 100644
--- a/include/uapi/linux/elf.h
+++ b/include/uapi/linux/elf.h
@@ -440,6 +440,7 @@ typedef struct elf64_shdr {
#define NT_ARM_SSVE 0x40b /* ARM Streaming SVE registers */
#define NT_ARM_ZA 0x40c /* ARM SME ZA registers */
#define NT_ARM_ZT 0x40d /* ARM SME ZT registers */
+#define NT_ARM_GCS 0x40e /* ARM GCS state */
#define NT_ARC_V2 0x600 /* ARCv2 accumulator/extra registers */
#define NT_VMCOREDD 0x700 /* Vmcore Device Dump Note */
#define NT_MIPS_DSP 0x800 /* MIPS DSP ASE registers */

--
2.30.2