[PATCH] fixup! arm64: Introduce prctl() options to control the tagged user addresses ABI

[Catalin Marinas]

Rename abi.tagged_addr sysctl control to abi.tagged_addr_disabled,
defaulting to 0. Only prevent prctl(PR_TAGGED_ADDR_ENABLE)from being
called when abi.tagged_addr_disabled==1.

Force unused arg* of the new prctl() to 0.

Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
---
 arch/arm64/kernel/process.c | 17 ++++++++++-------
 kernel/sys.c                |  4 ++++
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 76b7c55026aa..03689c0beb34 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -579,17 +579,22 @@ void arch_setup_new_exec(void)
 /*
  * Control the relaxed ABI allowing tagged user addresses into the kernel.
  */
-static unsigned int tagged_addr_prctl_allowed = 1;
+static unsigned int tagged_addr_disabled;
 
 long set_tagged_addr_ctrl(unsigned long arg)
 {
-	if (!tagged_addr_prctl_allowed)
-		return -EINVAL;
 	if (is_compat_task())
 		return -EINVAL;
 	if (arg & ~PR_TAGGED_ADDR_ENABLE)
 		return -EINVAL;
 
+	/*
+	 * Do not allow the enabling of the tagged address ABI if globally
+	 * disabled via sysctl abi.tagged_addr_disabled.
+	 */
+	if (arg & PR_TAGGED_ADDR_ENABLE && tagged_addr_disabled)
+		return -EINVAL;
+
 	update_thread_flag(TIF_TAGGED_ADDR, arg & PR_TAGGED_ADDR_ENABLE);
 
 	return 0;
@@ -597,8 +602,6 @@ long set_tagged_addr_ctrl(unsigned long arg)
 
 long get_tagged_addr_ctrl(void)
 {
-	if (!tagged_addr_prctl_allowed)
-		return -EINVAL;
 	if (is_compat_task())
 		return -EINVAL;
 
@@ -618,9 +621,9 @@ static int one = 1;
 
 static struct ctl_table tagged_addr_sysctl_table[] = {
 	{
-		.procname	= "tagged_addr",
+		.procname	= "tagged_addr_disabled",
 		.mode		= 0644,
-		.data		= &tagged_addr_prctl_allowed,
+		.data		= &tagged_addr_disabled,
 		.maxlen		= sizeof(int),
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &zero,
diff --git a/kernel/sys.c b/kernel/sys.c
index c6c4d5358bd3..ec48396b4943 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2499,9 +2499,13 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 		error = PAC_RESET_KEYS(me, arg2);
 		break;
 	case PR_SET_TAGGED_ADDR_CTRL:
+		if (arg3 || arg4 || arg5)
+			return -EINVAL;
 		error = SET_TAGGED_ADDR_CTRL(arg2);
 		break;
 	case PR_GET_TAGGED_ADDR_CTRL:
+		if (arg2 || arg3 || arg4 || arg5)
+			return -EINVAL;
 		error = GET_TAGGED_ADDR_CTRL();
 		break;
 	default: