[PATCH v3 1/2] arm64: Support execute-only permissions with Enhanced PAN

Vladimir Murzin vladimir.murzin at arm.com
Tue Jan 19 11:07:22 EST 2021


Enhanced Privileged Access Never (EPAN) allows Privileged Access Never
to be used with Execute-only mappings.

Absence of such support was a reason for 24cecc377463 ("arm64: Revert
support for execute-only user mappings"). Thus now it can be revisited
and re-enabled.

Cc: Kees Cook <keescook at chromium.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin at arm.com>
---
 arch/arm64/Kconfig                    | 17 +++++++++++++++++
 arch/arm64/include/asm/cpucaps.h      |  3 ++-
 arch/arm64/include/asm/pgtable-prot.h |  5 +++--
 arch/arm64/include/asm/pgtable.h      | 14 +++++++++++++-
 arch/arm64/include/asm/sysreg.h       |  3 ++-
 arch/arm64/kernel/cpufeature.c        | 12 ++++++++++++
 arch/arm64/mm/fault.c                 |  3 +++
 7 files changed, 52 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index f39568b..e63cc18 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1053,6 +1053,9 @@ config ARCH_WANT_HUGE_PMD_SHARE
 config ARCH_HAS_CACHE_LINE_SIZE
 	def_bool y
 
+config ARCH_HAS_FILTER_PGPROT
+	def_bool y
+
 config ARCH_ENABLE_SPLIT_PMD_PTLOCK
 	def_bool y if PGTABLE_LEVELS > 2
 
@@ -1673,6 +1676,20 @@ config ARM64_MTE
 
 endmenu
 
+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.
+
+	 The feature is detected at runtime, and will remain disabled
+	 if the cpu does not implement the feature.
+endmenu
+
 config ARM64_SVE
 	bool "ARM Scalable Vector Extension support"
 	default y
diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index b77d997..9e3ec4d 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -66,7 +66,8 @@
 #define ARM64_WORKAROUND_1508412		58
 #define ARM64_HAS_LDAPR				59
 #define ARM64_KVM_PROTECTED_MODE		60
+#define ARM64_HAS_EPAN				61
 
-#define ARM64_NCAPS				61
+#define ARM64_NCAPS				62
 
 #endif /* __ASM_CPUCAPS_H */
diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index 046be78..f91c2aa 100644
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -88,12 +88,13 @@ extern bool arm64_use_ng_mappings;
 #define PAGE_SHARED_EXEC	__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_RDONLY | PTE_NG | PTE_PXN | PTE_WRITE)
 #define PAGE_READONLY		__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_RDONLY | PTE_NG | PTE_PXN | PTE_UXN)
 #define PAGE_READONLY_EXEC	__pgprot(_PAGE_DEFAULT | PTE_USER | PTE_RDONLY | PTE_NG | PTE_PXN)
+#define PAGE_EXECONLY		__pgprot(_PAGE_DEFAULT | PTE_RDONLY | PTE_NG | PTE_PXN)
 
 #define __P000  PAGE_NONE
 #define __P001  PAGE_READONLY
 #define __P010  PAGE_READONLY
 #define __P011  PAGE_READONLY
-#define __P100  PAGE_READONLY_EXEC
+#define __P100  PAGE_EXECONLY
 #define __P101  PAGE_READONLY_EXEC
 #define __P110  PAGE_READONLY_EXEC
 #define __P111  PAGE_READONLY_EXEC
@@ -102,7 +103,7 @@ extern bool arm64_use_ng_mappings;
 #define __S001  PAGE_READONLY
 #define __S010  PAGE_SHARED
 #define __S011  PAGE_SHARED
-#define __S100  PAGE_READONLY_EXEC
+#define __S100  PAGE_EXECONLY
 #define __S101  PAGE_READONLY_EXEC
 #define __S110  PAGE_SHARED_EXEC
 #define __S111  PAGE_SHARED_EXEC
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 5015627..0196849 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -114,7 +114,7 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
 
 #define pte_valid(pte)		(!!(pte_val(pte) & PTE_VALID))
 #define pte_valid_not_user(pte) \
-	((pte_val(pte) & (PTE_VALID | PTE_USER)) == PTE_VALID)
+	((pte_val(pte) & (PTE_VALID | PTE_USER | PTE_UXN)) == (PTE_VALID | PTE_UXN))
 #define pte_valid_user(pte) \
 	((pte_val(pte) & (PTE_VALID | PTE_USER)) == (PTE_VALID | PTE_USER))
 
@@ -982,6 +982,18 @@ static inline bool arch_faults_on_old_pte(void)
 }
 #define arch_faults_on_old_pte arch_faults_on_old_pte
 
+static inline pgprot_t arch_filter_pgprot(pgprot_t prot)
+{
+	if (cpus_have_const_cap(ARM64_HAS_EPAN))
+		return prot;
+
+	if (pgprot_val(prot) != pgprot_val(PAGE_EXECONLY))
+		return prot;
+
+	return PAGE_READONLY_EXEC;
+}
+
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __ASM_PGTABLE_H */
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 8b5e7e5..47e9fdc 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -591,6 +591,7 @@
 	(SCTLR_EL2_RES1 | ENDIAN_SET_EL2)
 
 /* SCTLR_EL1 specific flags. */
+#define SCTLR_EL1_EPAN		(BIT(57))
 #define SCTLR_EL1_ATA0		(BIT(42))
 
 #define SCTLR_EL1_TCF0_SHIFT	38
@@ -631,7 +632,7 @@
 	 SCTLR_EL1_SED  | SCTLR_ELx_I    | SCTLR_EL1_DZE  | SCTLR_EL1_UCT   | \
 	 SCTLR_EL1_NTWE | SCTLR_ELx_IESB | SCTLR_EL1_SPAN | SCTLR_ELx_ITFSB | \
 	 SCTLR_ELx_ATA  | SCTLR_EL1_ATA0 | ENDIAN_SET_EL1 | SCTLR_EL1_UCI   | \
-	 SCTLR_EL1_RES1)
+	 SCTLR_EL1_EPAN | SCTLR_EL1_RES1)
 
 /* MAIR_ELx memory attributes (used by Linux) */
 #define MAIR_ATTR_DEVICE_nGnRnE		UL(0x00)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index e99edde..9d85956 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1774,6 +1774,18 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.cpu_enable = cpu_enable_pan,
 	},
 #endif /* CONFIG_ARM64_PAN */
+#ifdef CONFIG_ARM64_EPAN
+	{
+		.desc = "Enhanced Privileged Access Never",
+		.capability = ARM64_HAS_EPAN,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.matches = has_cpuid_feature,
+		.sys_reg = SYS_ID_AA64MMFR1_EL1,
+		.field_pos = ID_AA64MMFR1_PAN_SHIFT,
+		.sign = FTR_UNSIGNED,
+		.min_field_value = 3,
+	},
+#endif /* CONFIG_ARM64_EPAN */
 #ifdef CONFIG_ARM64_LSE_ATOMICS
 	{
 		.desc = "LSE atomic instructions",
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 3c40da4..c32095f6 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -529,6 +529,9 @@ static int __kprobes do_page_fault(unsigned long far, unsigned int esr,
 	if (faulthandler_disabled() || !mm)
 		goto no_context;
 
+	if (cpus_have_const_cap(ARM64_HAS_EPAN))
+		vm_flags &= ~VM_EXEC;
+
 	if (user_mode(regs))
 		mm_flags |= FAULT_FLAG_USER;
 
-- 
2.7.4




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