arm64/sme: Implement ZT0 ptrace support

Implement support for a new note type NT_ARM64_ZT providing access to
ZT0 when implemented. Since ZT0 is a register with constant size this is
much simpler than for other SME state.

As ZT0 is only accessible when PSTATE.ZA is set writes to ZT0 cause
PSTATE.ZA to be set, the main alternative would be to return -EBUSY in
this case but this seemed more constructive. Practical users are also
going to be working with ZA anyway and have some understanding of the
state.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221208-arm64-sme2-v4-12-f2fa0aef982f@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 54 insertions, 0 deletions

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 67256e7772e4..38be7ca202af 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -1138,6 +1138,51 @@ out:
 	return ret;
 }
 
+static int zt_get(struct task_struct *target,
+		  const struct user_regset *regset,
+		  struct membuf to)
+{
+	if (!system_supports_sme2())
+		return -EINVAL;
+
+	/*
+	 * If PSTATE.ZA is not set then ZT will be zeroed when it is
+	 * enabled so report the current register value as zero.
+	 */
+	if (thread_za_enabled(&target->thread))
+		membuf_write(&to, thread_zt_state(&target->thread),
+			     ZT_SIG_REG_BYTES);
+	else
+		membuf_zero(&to, ZT_SIG_REG_BYTES);
+
+	return 0;
+}
+
+static int zt_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;
+
+	if (!system_supports_sme2())
+		return -EINVAL;
+
+	if (!thread_za_enabled(&target->thread)) {
+		sme_alloc(target);
+		if (!target->thread.sme_state)
+			return -ENOMEM;
+	}
+
+	ret = user_regset_copyin(&pos, &count, &kbuf, &ubuf,
+				 thread_zt_state(&target->thread),
+				 0, ZT_SIG_REG_BYTES);
+	if (ret == 0)
+		target->thread.svcr |= SVCR_ZA_MASK;
+
+	return ret;
+}
+
 #endif /* CONFIG_ARM64_SME */
 
 #ifdef CONFIG_ARM64_PTR_AUTH
@@ -1360,6 +1405,7 @@ enum aarch64_regset {
 #ifdef CONFIG_ARM64_SVE
 	REGSET_SSVE,
 	REGSET_ZA,
+	REGSET_ZT,
 #endif
 #ifdef CONFIG_ARM64_PTR_AUTH
 	REGSET_PAC_MASK,
@@ -1467,6 +1513,14 @@ static const struct user_regset aarch64_regsets[] = {
 		.regset_get = za_get,
 		.set = za_set,
 	},
+	[REGSET_ZT] = { /* SME ZT */
+		.core_note_type = NT_ARM_ZT,
+		.n = 1,
+		.size = ZT_SIG_REG_BYTES,
+		.align = sizeof(u64),
+		.regset_get = zt_get,
+		.set = zt_set,
+	},
 #endif
 #ifdef CONFIG_ARM64_PTR_AUTH
 	[REGSET_PAC_MASK] = {