Commit 018a231b authored by Marc Zyngier's avatar Marc Zyngier Committed by Will Deacon
Browse files

arm64: Unconditionally enable PAN support 



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: default avatarMarc Zyngier <maz@kernel.org>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 6191b25d

arch/arm64/Kconfig

+0 −17
Original line number Diff line number Diff line
@@ -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.

arch/arm64/include/asm/cpucaps.h

+0 −2
Original line number Diff line number Diff line
@@ -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:

arch/arm64/include/asm/uaccess.h

+2 −4
Original line number Diff line number Diff line
@@ -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)

arch/arm64/kernel/cpufeature.c

+0 −4
Original line number Diff line number Diff line
@@ -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",

arch/arm64/kvm/hyp/entry.S

+1 −1
Original line number Diff line number Diff line
@@ -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)]