arm64: Ensure execute-only permissions are not allowed without EPAN

Commit 18107f8a ("arm64: Support execute-only permissions with
Enhanced PAN") re-introduced execute-only permissions when EPAN is
available. When EPAN is not available, arch_filter_pgprot() is supposed
to change a PAGE_EXECONLY permission into PAGE_READONLY_EXEC. However,
if BTI or MTE are present, such check does not detect the execute-only
pgprot in the presence of PTE_GP (BTI) or MT_NORMAL_TAGGED (MTE),
allowing the user to request PROT_EXEC with PROT_BTI or PROT_MTE.

Remove the arch_filter_pgprot() function, change the default VM_EXEC
permissions to PAGE_READONLY_EXEC and update the protection_map[] array
at core_initcall() if EPAN is detected.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Fixes: 18107f8a ("arm64: Support execute-only permissions with Enhanced PAN")
Cc: <stable@vger.kernel.org> # 5.13.x
Acked-by: Will Deacon <will@kernel.org>
Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com>
Tested-by: Vladimir Murzin <vladimir.murzin@arm.com>

arch/arm64/Kconfig

@@ -1236,9 +1236,6 @@ config HW_PERF_EVENTS
 	def_bool y
 	depends on ARM_PMU
 
-config ARCH_HAS_FILTER_PGPROT
-	def_bool y
-
 # Supported by clang >= 7.0
 config CC_HAVE_SHADOW_CALL_STACK
 	def_bool $(cc-option, -fsanitize=shadow-call-stack -ffixed-x18)

arch/arm64/include/asm/pgtable-prot.h

@@ -92,7 +92,7 @@ extern bool arm64_use_ng_mappings;
 #define __P001  PAGE_READONLY
 #define __P010  PAGE_READONLY
 #define __P011  PAGE_READONLY
-#define __P100  PAGE_EXECONLY
+#define __P100  PAGE_READONLY_EXEC	/* PAGE_EXECONLY if Enhanced PAN */
 #define __P101  PAGE_READONLY_EXEC
 #define __P110  PAGE_READONLY_EXEC
 #define __P111  PAGE_READONLY_EXEC
@@ -101,7 +101,7 @@ extern bool arm64_use_ng_mappings;
 #define __S001  PAGE_READONLY
 #define __S010  PAGE_SHARED
 #define __S011  PAGE_SHARED
-#define __S100  PAGE_EXECONLY
+#define __S100  PAGE_READONLY_EXEC	/* PAGE_EXECONLY if Enhanced PAN */
 #define __S101  PAGE_READONLY_EXEC
 #define __S110  PAGE_SHARED_EXEC
 #define __S111  PAGE_SHARED_EXEC

arch/arm64/include/asm/pgtable.h

@@ -1017,17 +1017,6 @@ static inline bool arch_wants_old_prefaulted_pte(void)
 }
 #define arch_wants_old_prefaulted_pte	arch_wants_old_prefaulted_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;
-}
-
 static inline bool pud_sect_supported(void)
 {
 	return PAGE_SIZE == SZ_4K;

arch/arm64/mm/mmap.c

@@ -7,8 +7,10 @@
 
 #include <linux/io.h>
 #include <linux/memblock.h>
+#include <linux/mm.h>
 #include <linux/types.h>
 
+#include <asm/cpufeature.h>
 #include <asm/page.h>
 
 /*
@@ -38,3 +40,18 @@ int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
 {
 	return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
 }
+
+static int __init adjust_protection_map(void)
+{
+	/*
+	 * With Enhanced PAN we can honour the execute-only permissions as
+	 * there is no PAN override with such mappings.
+	 */
+	if (cpus_have_const_cap(ARM64_HAS_EPAN)) {
+		protection_map[VM_EXEC] = PAGE_EXECONLY;
+		protection_map[VM_EXEC | VM_SHARED] = PAGE_EXECONLY;
+	}
+
+	return 0;
+}
+arch_initcall(adjust_protection_map);