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From: Vladimir Murzin <vladimir.murzin@arm.com>
To: linux-arm-kernel@lists.infradead.org
Cc: catalin.marinas@arm.com, keescook@chromium.org
Subject: [PATCH 1/2] arm64: Support execute-only permissions with Enhanced PAN
Date: Thu, 19 Nov 2020 13:39:52 +0000	[thread overview]
Message-ID: <20201119133953.15585-2-vladimir.murzin@arm.com> (raw)
In-Reply-To: <20201119133953.15585-1-vladimir.murzin@arm.com>

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@chromium.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
---
 arch/arm64/Kconfig                    | 17 +++++++++++++++++
 arch/arm64/include/asm/cpucaps.h      |  5 +++--
 arch/arm64/include/asm/pgtable-prot.h |  5 +++--
 arch/arm64/include/asm/pgtable.h      | 14 +++++++++++++-
 arch/arm64/include/asm/sysreg.h       |  1 +
 arch/arm64/kernel/cpufeature.c        | 21 +++++++++++++++++++++
 arch/arm64/mm/fault.c                 |  3 +++
 7 files changed, 61 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 1515f6f..6639244 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1056,6 +1056,9 @@ 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
 
@@ -1688,6 +1691,20 @@ 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 e7d9899..3ea4fbdf 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -22,7 +22,7 @@
 #define ARM64_WORKAROUND_CAVIUM_27456		12
 #define ARM64_HAS_32BIT_EL0			13
 #define ARM64_HARDEN_EL2_VECTORS		14
-#define ARM64_HAS_CNP				15
+#define ARM64_HAS_EPAN				15
 #define ARM64_HAS_NO_FPSIMD			16
 #define ARM64_WORKAROUND_REPEAT_TLBI		17
 #define ARM64_WORKAROUND_QCOM_FALKOR_E1003	18
@@ -66,7 +66,8 @@
 #define ARM64_HAS_TLB_RANGE			56
 #define ARM64_MTE				57
 #define ARM64_WORKAROUND_1508412		58
+#define ARM64_HAS_CNP				59
 
-#define ARM64_NCAPS				59
+#define ARM64_NCAPS				60
 
 #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 4ff12a7..e4ab9e0 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_young(pte) \
 	((pte_val(pte) & (PTE_VALID | PTE_AF)) == (PTE_VALID | PTE_AF))
 #define pte_valid_user(pte) \
@@ -974,6 +974,18 @@ 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 174817b..19147b6 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -579,6 +579,7 @@
 #endif
 
 /* SCTLR_EL1 specific flags. */
+#define SCTLR_EL1_EPAN		(BIT(57))
 #define SCTLR_EL1_ATA0		(BIT(42))
 
 #define SCTLR_EL1_TCF0_SHIFT	38
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index dcc165b..540245c 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1602,6 +1602,14 @@ static void cpu_enable_pan(const struct arm64_cpu_capabilities *__unused)
 }
 #endif /* CONFIG_ARM64_PAN */
 
+#ifdef CONFIG_ARM64_EPAN
+static void cpu_enable_epan(const struct arm64_cpu_capabilities *__unused)
+{
+	sysreg_clear_set(sctlr_el1, 0, SCTLR_EL1_EPAN);
+	local_flush_tlb_all();
+}
+#endif /* CONFIG_ARM64_EPAN */
+
 #ifdef CONFIG_ARM64_RAS_EXTN
 static void cpu_clear_disr(const struct arm64_cpu_capabilities *__unused)
 {
@@ -1750,6 +1758,19 @@ 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,
+		.cpu_enable = cpu_enable_epan,
+	},
+#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 1ee9400..b93222e 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -467,6 +467,9 @@ static int __kprobes do_page_fault(unsigned long addr, 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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  reply	other threads:[~2020-11-19 13:40 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-19 13:39 [PATCH 0/2] arm64: Support Enhanced PAN Vladimir Murzin
2020-11-19 13:39 ` Vladimir Murzin [this message]
2020-11-19 18:22   ` [PATCH 1/2] arm64: Support execute-only permissions with " Catalin Marinas
2020-11-19 18:52   ` Dave Martin
2020-11-27 18:31     ` Catalin Marinas
2020-12-02 18:23   ` Catalin Marinas
2020-12-08 11:41     ` Vladimir Murzin
2020-11-19 13:39 ` [PATCH 2/2] arm64: Introduce HWCAPS2_EXECONLY Vladimir Murzin
2020-12-08 16:36   ` Dave Martin
2020-12-08 17:34     ` Catalin Marinas

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