[PATCH 2/3] arm64: Unconditionally enable PAN support

Marc Zyngier
2026-01-07T18:07:08Z

FEAT_PAN has been around since ARMv8.1 (over 11 years ago), has no compiler
dependency (we have our own accessors), and is a great security benefit.

Drop CONFIG_ARM64_PAN, and make the support unconditionnal.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/Kconfig | 17 -----------------
arch/arm64/include/asm/cpucaps.h | 2 --
arch/arm64/include/asm/uaccess.h | 6 ++----
arch/arm64/kernel/cpufeature.c | 4 ----
arch/arm64/kvm/hyp/entry.S | 2 +-
5 files changed, 3 insertions(+), 28 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index b6f57cc1e4df8..fcfb62ec4bae8 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1680,7 +1680,6 @@ config MITIGATE_SPECTRE_BRANCH_HISTORY
config ARM64_SW_TTBR0_PAN
bool "Emulate Privileged Access Never using TTBR0_EL1 switching"
depends on !KCSAN
- select ARM64_PAN
help
Enabling this option prevents the kernel from accessing
user-space memory directly by pointing TTBR0_EL1 to a reserved
@@ -1859,20 +1858,6 @@ config ARM64_HW_AFDBM
to work on pre-ARMv8.1 hardware and the performance impact is
minimal. If unsure, say Y.

-config ARM64_PAN
- bool "Enable support for Privileged Access Never (PAN)"
- default y
- help
- Privileged Access Never (PAN; part of the ARMv8.1 Extensions)
- prevents the kernel or hypervisor from accessing user-space (EL0)
- memory directly.
-
- Choosing this option will cause any unprotected (not using
- copy_to_user et al) memory access to fail with a permission fault.
-
- The feature is detected at runtime, and will remain as a 'nop'
- instruction if the cpu does not implement the feature.
-
endmenu # "ARMv8.1 architectural features"

menu "ARMv8.2 architectural features"
@@ -2109,7 +2094,6 @@ config ARM64_MTE
depends on ARM64_AS_HAS_MTE && ARM64_TAGGED_ADDR_ABI
depends on AS_HAS_ARMV8_5
# Required for tag checking in the uaccess routines
- select ARM64_PAN
select ARCH_HAS_SUBPAGE_FAULTS
select ARCH_USES_HIGH_VMA_FLAGS
select ARCH_USES_PG_ARCH_2
@@ -2141,7 +2125,6 @@ menu "ARMv8.7 architectural features"
config ARM64_EPAN
bool "Enable support for Enhanced Privileged Access Never (EPAN)"
default y
- depends on ARM64_PAN
help
Enhanced Privileged Access Never (EPAN) allows Privileged
Access Never to be used with Execute-only mappings.
diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index 2c8029472ad45..177c691914f87 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -19,8 +19,6 @@ cpucap_is_possible(const unsigned int cap)
"cap must be < ARM64_NCAPS");

switch (cap) {
- case ARM64_HAS_PAN:
- return IS_ENABLED(CONFIG_ARM64_PAN);
case ARM64_HAS_EPAN:
return IS_ENABLED(CONFIG_ARM64_EPAN);
case ARM64_SVE:
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 6490930deef84..9810106a3f664 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -124,14 +124,12 @@ static inline bool uaccess_ttbr0_enable(void)

static inline void __uaccess_disable_hw_pan(void)
{
- asm(ALTERNATIVE("nop", SET_PSTATE_PAN(0), ARM64_HAS_PAN,
- CONFIG_ARM64_PAN));
+ asm(ALTERNATIVE("nop", SET_PSTATE_PAN(0), ARM64_HAS_PAN));
}

static inline void __uaccess_enable_hw_pan(void)
{
- asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_HAS_PAN,
- CONFIG_ARM64_PAN));
+ asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_HAS_PAN));
}

static inline void uaccess_disable_privileged(void)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 547ccf28f2893..716440d147a2d 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2164,7 +2164,6 @@ static bool has_bbml2_noabort(const struct arm64_cpu_capabilities *caps, int sco
return cpu_supports_bbml2_noabort();
}

-#ifdef CONFIG_ARM64_PAN
static void cpu_enable_pan(const struct arm64_cpu_capabilities *__unused)
{
/*
@@ -2176,7 +2175,6 @@ static void cpu_enable_pan(const struct arm64_cpu_capabilities *__unused)
sysreg_clear_set(sctlr_el1, SCTLR_EL1_SPAN, 0);
set_pstate_pan(1);
}
-#endif /* CONFIG_ARM64_PAN */

#ifdef CONFIG_ARM64_RAS_EXTN
static void cpu_clear_disr(const struct arm64_cpu_capabilities *__unused)
@@ -2541,7 +2539,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.matches = has_cpuid_feature,
ARM64_CPUID_FIELDS(ID_AA64MMFR0_EL1, ECV, CNTPOFF)
},
-#ifdef CONFIG_ARM64_PAN
{
.desc = "Privileged Access Never",
.capability = ARM64_HAS_PAN,
@@ -2550,7 +2547,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.cpu_enable = cpu_enable_pan,
ARM64_CPUID_FIELDS(ID_AA64MMFR1_EL1, PAN, IMP)
},
-#endif /* CONFIG_ARM64_PAN */
#ifdef CONFIG_ARM64_EPAN
{
.desc = "Enhanced Privileged Access Never",
diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index 9f4e8d68ab505..11a10d8f5beb2 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -126,7 +126,7 @@ SYM_INNER_LABEL(__guest_exit, SYM_L_GLOBAL)

add x1, x1, #VCPU_CONTEXT

- ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN, CONFIG_ARM64_PAN)
+ ALTERNATIVE(nop, SET_PSTATE_PAN(1), ARM64_HAS_PAN)

// Store the guest regs x2 and x3
stp x2, x3, [x1, #CPU_XREG_OFFSET(2)]
--
2.47.3