arm64: mte: Add PROT_MTE support to mmap() and mprotect()

To enable tagging on a memory range, the user must explicitly opt in via
a new PROT_MTE flag passed to mmap() or mprotect(). Since this is a new
memory type in the AttrIndx field of a pte, simplify the or'ing of these
bits over the protection_map[] attributes by making MT_NORMAL index 0.

There are two conditions for arch_vm_get_page_prot() to return the
MT_NORMAL_TAGGED memory type: (1) the user requested it via PROT_MTE,
registered as VM_MTE in the vm_flags, and (2) the vma supports MTE,
decided during the mmap() call (only) and registered as VM_MTE_ALLOWED.

arch_calc_vm_prot_bits() is responsible for registering the user request
as VM_MTE. The newly introduced arch_calc_vm_flag_bits() sets
VM_MTE_ALLOWED if the mapping is MAP_ANONYMOUS. An MTE-capable
filesystem (RAM-based) may be able to set VM_MTE_ALLOWED during its
mmap() file ops call.

In addition, update VM_DATA_DEFAULT_FLAGS to allow mprotect(PROT_MTE) on
stack or brk area.

The Linux mmap() syscall currently ignores unknown PROT_* flags. In the
presence of MTE, an mmap(PROT_MTE) on a file which does not support MTE
will not report an error and the memory will not be mapped as Normal
Tagged. For consistency, mprotect(PROT_MTE) will not report an error
either if the memory range does not support MTE. Two subsequent patches
in the series will propose tightening of this behaviour.
Co-developed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>

arch/arm64/include/asm/memory.h

@@ -126,14 +126,18 @@
 
 /*
  * Memory types available.
+ *
+ * IMPORTANT: MT_NORMAL must be index 0 since vm_get_page_prot() may 'or' in
+ *	      the MT_NORMAL_TAGGED memory type for PROT_MTE mappings. Note
+ *	      that protection_map[] only contains MT_NORMAL attributes.
  */
-#define MT_DEVICE_nGnRnE	0
-#define MT_DEVICE_nGnRE		1
-#define MT_DEVICE_GRE		2
-#define MT_NORMAL_NC		3
-#define MT_NORMAL		4
-#define MT_NORMAL_WT		5
-#define MT_NORMAL_TAGGED	6
+#define MT_NORMAL		0
+#define MT_NORMAL_TAGGED	1
+#define MT_NORMAL_NC		2
+#define MT_NORMAL_WT		3
+#define MT_DEVICE_nGnRnE	4
+#define MT_DEVICE_nGnRE		5
+#define MT_DEVICE_GRE		6
 
 /*
  * Memory types for Stage-2 translation

arch/arm64/include/asm/mman.h

@@ -9,16 +9,51 @@
 static inline unsigned long arch_calc_vm_prot_bits(unsigned long prot,
 	unsigned long pkey __always_unused)
 {
+	unsigned long ret = 0;
+
 	if (system_supports_bti() && (prot & PROT_BTI))
-		return VM_ARM64_BTI;
+		ret |= VM_ARM64_BTI;
 
-	return 0;
+	if (system_supports_mte() && (prot & PROT_MTE))
+		ret |= VM_MTE;
+
+	return ret;
 }
 #define arch_calc_vm_prot_bits(prot, pkey) arch_calc_vm_prot_bits(prot, pkey)
 
+static inline unsigned long arch_calc_vm_flag_bits(unsigned long flags)
+{
+	/*
+	 * Only allow MTE on anonymous mappings as these are guaranteed to be
+	 * backed by tags-capable memory. The vm_flags may be overridden by a
+	 * filesystem supporting MTE (RAM-based).
+	 */
+	if (system_supports_mte() && (flags & MAP_ANONYMOUS))
+		return VM_MTE_ALLOWED;
+
+	return 0;
+}
+#define arch_calc_vm_flag_bits(flags) arch_calc_vm_flag_bits(flags)
+
 static inline pgprot_t arch_vm_get_page_prot(unsigned long vm_flags)
 {
-	return (vm_flags & VM_ARM64_BTI) ? __pgprot(PTE_GP) : __pgprot(0);
+	pteval_t prot = 0;
+
+	if (vm_flags & VM_ARM64_BTI)
+		prot |= PTE_GP;
+
+	/*
+	 * There are two conditions required for returning a Normal Tagged
+	 * memory type: (1) the user requested it via PROT_MTE passed to
+	 * mmap() or mprotect() and (2) the corresponding vma supports MTE. We
+	 * register (1) as VM_MTE in the vma->vm_flags and (2) as
+	 * VM_MTE_ALLOWED. Note that the latter can only be set during the
+	 * mmap() call since mprotect() does not accept MAP_* flags.
+	 */
+	if ((vm_flags & VM_MTE) && (vm_flags & VM_MTE_ALLOWED))
+		prot |= PTE_ATTRINDX(MT_NORMAL_TAGGED);
+
+	return __pgprot(prot);
 }
 #define arch_vm_get_page_prot(vm_flags) arch_vm_get_page_prot(vm_flags)
 
@@ -30,6 +65,9 @@ static inline bool arch_validate_prot(unsigned long prot,
 	if (system_supports_bti())
 		supported |= PROT_BTI;
 
+	if (system_supports_mte())
+		supported |= PROT_MTE;
+
 	return (prot & ~supported) == 0;
 }
 #define arch_validate_prot(prot, addr) arch_validate_prot(prot, addr)

arch/arm64/include/asm/page.h

@@ -43,7 +43,7 @@ extern int pfn_valid(unsigned long);
 
 #endif /* !__ASSEMBLY__ */
 
-#define VM_DATA_DEFAULT_FLAGS	VM_DATA_FLAGS_TSK_EXEC
+#define VM_DATA_DEFAULT_FLAGS	(VM_DATA_FLAGS_TSK_EXEC | VM_MTE_ALLOWED)
 
 #include <asm-generic/getorder.h>
 

arch/arm64/include/asm/pgtable.h

@@ -681,8 +681,13 @@ static inline unsigned long p4d_page_vaddr(p4d_t p4d)
 
 static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 {
+	/*
+	 * Normal and Normal-Tagged are two different memory types and indices
+	 * in MAIR_EL1. The mask below has to include PTE_ATTRINDX_MASK.
+	 */
 	const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY |
-			      PTE_PROT_NONE | PTE_VALID | PTE_WRITE | PTE_GP;
+			      PTE_PROT_NONE | PTE_VALID | PTE_WRITE | PTE_GP |
+			      PTE_ATTRINDX_MASK;
 	/* preserve the hardware dirty information */
 	if (pte_hw_dirty(pte))
 		pte = pte_mkdirty(pte);

arch/arm64/include/uapi/asm/mman.h

@@ -5,5 +5,6 @@
 #include <asm-generic/mman.h>
 
 #define PROT_BTI	0x10		/* BTI guarded page */
+#define PROT_MTE	0x20		/* Normal Tagged mapping */
 
 #endif /* ! _UAPI__ASM_MMAN_H */

fs/proc/task_mmu.c

@@ -653,6 +653,10 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
 		[ilog2(VM_MERGEABLE)]	= "mg",
 		[ilog2(VM_UFFD_MISSING)]= "um",
 		[ilog2(VM_UFFD_WP)]	= "uw",
+#ifdef CONFIG_ARM64_MTE
+		[ilog2(VM_MTE)]		= "mt",
+		[ilog2(VM_MTE_ALLOWED)]	= "",
+#endif
 #ifdef CONFIG_ARCH_HAS_PKEYS
 		/* These come out via ProtectionKey: */
 		[ilog2(VM_PKEY_BIT0)]	= "",

include/linux/mm.h

@@ -340,6 +340,14 @@ extern unsigned int kobjsize(const void *objp);
 # define VM_MAPPED_COPY	VM_ARCH_1	/* T if mapped copy of data (nommu mmap) */
 #endif
 
+#if defined(CONFIG_ARM64_MTE)
+# define VM_MTE		VM_HIGH_ARCH_0	/* Use Tagged memory for access control */
+# define VM_MTE_ALLOWED	VM_HIGH_ARCH_1	/* Tagged memory permitted */
+#else
+# define VM_MTE		VM_NONE
+# define VM_MTE_ALLOWED	VM_NONE
+#endif
+
 #ifndef VM_GROWSUP
 # define VM_GROWSUP	VM_NONE
 #endif