linux-kernel - [RFC PATCH v2 5/8] mm: kpkeys: Introduce cred pkey/level

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Message-ID: <20250815090000.2182450-6-kevin.brodsky@arm.com>
Date: Fri, 15 Aug 2025 09:59:57 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: linux-hardening@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Kevin Brodsky <kevin.brodsky@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	David Howells <dhowells@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Jann Horn <jannh@...gle.com>,
	Jeff Xu <jeffxu@...omium.org>,
	Joey Gouly <joey.gouly@....com>,
	Kees Cook <kees@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Marc Zyngier <maz@...nel.org>,
	Mark Brown <broonie@...nel.org>,
	Matthew Wilcox <willy@...radead.org>,
	Maxwell Bland <mbland@...orola.com>,
	"Mike Rapoport (IBM)" <rppt@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Pierre Langlois <pierre.langlois@....com>,
	Quentin Perret <qperret@...gle.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vlastimil Babka <vbabka@...e.cz>,
	Will Deacon <will@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-mm@...ck.org,
	x86@...nel.org
Subject: [RFC PATCH v2 5/8] mm: kpkeys: Introduce cred pkey/level

We will need a separate pkey to protect struct cred. Allocate one as
well as a new kpkeys level that grants write access to that pkey.

Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
---
 arch/arm64/include/asm/kpkeys.h | 7 ++++++-
 include/asm-generic/kpkeys.h    | 4 ++++
 include/linux/kpkeys.h          | 3 ++-
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kpkeys.h b/arch/arm64/include/asm/kpkeys.h
index ded5d6e988dc..ffb7622391c3 100644
--- a/arch/arm64/include/asm/kpkeys.h
+++ b/arch/arm64/include/asm/kpkeys.h
@@ -13,7 +13,8 @@
  * used in assembly.
  */
 #define POR_EL1_INIT	(POR_ELx_PERM_PREP(KPKEYS_PKEY_DEFAULT, POE_RWX) | \
-			 POR_ELx_PERM_PREP(KPKEYS_PKEY_PGTABLES, POE_R))
+			 POR_ELx_PERM_PREP(KPKEYS_PKEY_PGTABLES, POE_R) | \
+			 POR_ELx_PERM_PREP(KPKEYS_PKEY_CRED, POE_R))
 
 #ifndef __ASSEMBLY__
 
@@ -31,6 +32,10 @@ static inline u64 por_set_kpkeys_level(u64 por, int level)
 				     level == KPKEYS_LVL_PGTABLES ||
 				     level == KPKEYS_LVL_UNRESTRICTED
 				     ? POE_RW : POE_R);
+	por = por_elx_set_pkey_perms(por, KPKEYS_PKEY_CRED,
+				     level == KPKEYS_LVL_CRED ||
+				     level == KPKEYS_LVL_UNRESTRICTED
+				     ? POE_RW : POE_R);
 
 	return por;
 }
diff --git a/include/asm-generic/kpkeys.h b/include/asm-generic/kpkeys.h
index cec92334a9f3..56a2fc9fe4a6 100644
--- a/include/asm-generic/kpkeys.h
+++ b/include/asm-generic/kpkeys.h
@@ -2,6 +2,10 @@
 #ifndef __ASM_GENERIC_KPKEYS_H
 #define __ASM_GENERIC_KPKEYS_H
 
+#ifndef KPKEYS_PKEY_CRED
+#define KPKEYS_PKEY_CRED	2
+#endif
+
 #ifndef KPKEYS_PKEY_PGTABLES
 #define KPKEYS_PKEY_PGTABLES	1
 #endif
diff --git a/include/linux/kpkeys.h b/include/linux/kpkeys.h
index 48f240bea8e1..0e555b505b33 100644
--- a/include/linux/kpkeys.h
+++ b/include/linux/kpkeys.h
@@ -10,7 +10,8 @@ struct folio;
 
 #define KPKEYS_LVL_DEFAULT	0
 #define KPKEYS_LVL_PGTABLES	1
-#define KPKEYS_LVL_UNRESTRICTED	2
+#define KPKEYS_LVL_CRED		2
+#define KPKEYS_LVL_UNRESTRICTED	3
 
 #define KPKEYS_LVL_MIN		KPKEYS_LVL_DEFAULT
 #define KPKEYS_LVL_MAX		KPKEYS_LVL_UNRESTRICTED
-- 
2.47.0