[tip: x86/mm] x86/pkeys: Skip 'init_pkru' debugfs file creation when pkeys not supported

[tip-bot2 for Dave Hansen]

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     314a1e1eabea5b86532e90e0d4e217fa88471e3b
Gitweb:        https://git.kernel.org/tip/314a1e1eabea5b86532e90e0d4e217fa88471e3b
Author:        Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
AuthorDate:    Thu, 03 Jun 2021 16:08:10 -07:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Fri, 04 Jun 2021 17:01:03 +02:00

x86/pkeys: Skip 'init_pkru' debugfs file creation when pkeys not supported

The PKRU hardware is permissive by default: all reads and writes are
allowed.  The in-kernel policy is restrictive by default: deny all
unnecessary access until explicitly requested.

That policy can be modified with a debugfs file: "x86/init_pkru".
This file is created unconditionally, regardless of PKRU support in
the hardware, which is a little silly.

Avoid creating the file when pkeys are not available.  This also
removes the need to check for pkey support at runtime, which would be
required once the new pkey modification infrastructure is put in place
later in this series.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lkml.kernel.org/r/20210603230810.113FF3F2@xxxxxxxxxxxxxxxxxx
---
 arch/x86/mm/pkeys.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/mm/pkeys.c b/arch/x86/mm/pkeys.c
index a2332ee..4a67b92 100644
--- a/arch/x86/mm/pkeys.c
+++ b/arch/x86/mm/pkeys.c
@@ -192,6 +192,10 @@ static const struct file_operations fops_init_pkru = {
 
 static int __init create_init_pkru_value(void)
 {
+	/* Do not expose the file if pkeys are not supported. */
+	if (!cpu_feature_enabled(X86_FEATURE_OSPKE))
+		return 0;
+
 	debugfs_create_file("init_pkru", S_IRUSR | S_IWUSR,
 			arch_debugfs_dir, NULL, &fops_init_pkru);
 	return 0;