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

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Message-ID: <20250203102809.1223255-6-kevin.brodsky@arm.com>
Date: Mon,  3 Feb 2025 10:28:06 +0000
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>,
	Mark Brown <broonie@...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>,
	Andy Lutomirski <luto@...nel.org>,
	Marc Zyngier <maz@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Pierre Langlois <pierre.langlois@....com>,
	Quentin Perret <qperret@...gle.com>,
	"Mike Rapoport (IBM)" <rppt@...nel.org>,
	Ryan Roberts <ryan.roberts@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will@...nel.org>,
	Matthew Wilcox <willy@...radead.org>,
	Qi Zheng <zhengqi.arch@...edance.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-mm@...ck.org,
	x86@...nel.org
Subject: [RFC PATCH 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,
and add a guard that switches to that level.

Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
---
 arch/arm64/include/asm/kpkeys.h | 4 ++++
 include/asm-generic/kpkeys.h    | 4 ++++
 include/linux/kpkeys.h          | 9 ++++++++-
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/kpkeys.h b/arch/arm64/include/asm/kpkeys.h
index ab2305ca24b7..f5797e579fb9 100644
--- a/arch/arm64/include/asm/kpkeys.h
+++ b/arch/arm64/include/asm/kpkeys.h
@@ -22,6 +22,10 @@ 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_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 c5d804c1ab7b..a478eaf2e14f 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
@@ -160,4 +161,10 @@ KPKEYS_GUARD(kpkeys_rcu, KPKEYS_LVL_UNRESTRICTED)
 KPKEYS_GUARD_NOOP(kpkeys_rcu)
 #endif
 
+#ifdef CONFIG_KPKEYS_HARDENED_CRED
+KPKEYS_GUARD(kpkeys_hardened_cred, KPKEYS_LVL_CRED)
+#else
+KPKEYS_GUARD_NOOP(kpkeys_hardened_cred)
+#endif
+
 #endif /* _LINUX_KPKEYS_H */
-- 
2.47.0