linux-kernel - [RFC PATCH 04/16] arm64: Introduce por_set_pkey

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Message-ID: <20241206101110.1646108-5-kevin.brodsky@arm.com>
Date: Fri,  6 Dec 2024 10:10:58 +0000
From: Kevin Brodsky <kevin.brodsky@....com>
To: linux-hardening@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
	Kevin Brodsky <kevin.brodsky@....com>,
	aruna.ramakrishna@...cle.com,
	broonie@...nel.org,
	catalin.marinas@....com,
	dave.hansen@...ux.intel.com,
	jannh@...gle.com,
	jeffxu@...omium.org,
	joey.gouly@....com,
	kees@...nel.org,
	maz@...nel.org,
	pierre.langlois@....com,
	qperret@...gle.com,
	ryan.roberts@....com,
	will@...nel.org,
	linux-arm-kernel@...ts.infradead.org,
	x86@...nel.org
Subject: [RFC PATCH 04/16] arm64: Introduce por_set_pkey_perms() helper

Introduce a helper that sets the permissions of a given pkey
(POIndex) in the POR_ELx format, and make use of it in
arch_set_user_pkey_access().

Also ensure that <asm/sysreg.h> is included in asm/por.h to provide
the POE_* definitions.

Signed-off-by: Kevin Brodsky <kevin.brodsky@....com>
---
 arch/arm64/include/asm/por.h |  9 +++++++++
 arch/arm64/mm/mmu.c          | 28 ++++++++++------------------
 2 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/arch/arm64/include/asm/por.h b/arch/arm64/include/asm/por.h
index e06e9f473675..7f0d73980cce 100644
--- a/arch/arm64/include/asm/por.h
+++ b/arch/arm64/include/asm/por.h
@@ -6,6 +6,8 @@
 #ifndef _ASM_ARM64_POR_H
 #define _ASM_ARM64_POR_H
 
+#include <asm/sysreg.h>
+
 #define POR_BITS_PER_PKEY		4
 #define POR_ELx_IDX(por_elx, idx)	(((por_elx) >> ((idx) * POR_BITS_PER_PKEY)) & 0xf)
 
@@ -30,4 +32,11 @@ static inline bool por_elx_allows_exec(u64 por, u8 pkey)
 	return perm & POE_X;
 }
 
+static inline u64 por_set_pkey_perms(u64 por, u8 pkey, u64 perms)
+{
+	u64 shift = pkey * POR_BITS_PER_PKEY;
+
+	return (por & ~(POE_MASK << shift)) | (perms << shift);
+}
+
 #endif /* _ASM_ARM64_POR_H */
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index e2739b69e11b..20e0390ee382 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1554,9 +1554,8 @@ void __cpu_replace_ttbr1(pgd_t *pgdp, bool cnp)
 #ifdef CONFIG_ARCH_HAS_PKEYS
 int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, unsigned long init_val)
 {
-	u64 new_por = POE_RXW;
-	u64 old_por;
-	u64 pkey_shift;
+	u64 new_perms;
+	u64 por;
 
 	if (!system_supports_poe())
 		return -ENOSPC;
@@ -1570,26 +1569,19 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, unsigned long i
 		return -EINVAL;
 
 	/* Set the bits we need in POR:  */
-	new_por = POE_RXW;
+	new_perms = POE_RXW;
 	if (init_val & PKEY_DISABLE_WRITE)
-		new_por &= ~POE_W;
+		new_perms &= ~POE_W;
 	if (init_val & PKEY_DISABLE_ACCESS)
-		new_por &= ~POE_RW;
+		new_perms &= ~POE_RW;
 	if (init_val & PKEY_DISABLE_READ)
-		new_por &= ~POE_R;
+		new_perms &= ~POE_R;
 	if (init_val & PKEY_DISABLE_EXECUTE)
-		new_por &= ~POE_X;
+		new_perms &= ~POE_X;
 
-	/* Shift the bits in to the correct place in POR for pkey: */
-	pkey_shift = pkey * POR_BITS_PER_PKEY;
-	new_por <<= pkey_shift;
-
-	/* Get old POR and mask off any old bits in place: */
-	old_por = read_sysreg_s(SYS_POR_EL0);
-	old_por &= ~(POE_MASK << pkey_shift);
-
-	/* Write old part along with new part: */
-	write_sysreg_s(old_por | new_por, SYS_POR_EL0);
+	por = read_sysreg_s(SYS_POR_EL0);
+	por = por_set_pkey_perms(por, pkey, new_perms);
+	write_sysreg_s(por, SYS_POR_EL0);
 
 	return 0;
 }
-- 
2.47.0