[PATCH v5 12/25] arm64: mte: Add PROT_MTE support to mmap() and mprotect()

Catalin Marinas
2020-06-24T17:53:17Z

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>
---

Notes:
v2:
- Add VM_MTE_ALLOWED to show_smap_vma_flags().

arch/arm64/include/asm/memory.h | 18 +++++++-----
arch/arm64/include/asm/mman.h | 44 ++++++++++++++++++++++++++++--
arch/arm64/include/asm/page.h | 2 +-
arch/arm64/include/asm/pgtable.h | 7 ++++-
arch/arm64/include/uapi/asm/mman.h | 1 +
fs/proc/task_mmu.c | 4 +++
include/linux/mm.h | 8 ++++++
7 files changed, 72 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 472c77a68225..770535b7ca35 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -129,14 +129,18 @@

/*
* 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
diff --git a/arch/arm64/include/asm/mman.h b/arch/arm64/include/asm/mman.h
index 081ec8de9ea6..b01051be7750 100644
--- a/arch/arm64/include/asm/mman.h
+++ b/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)
diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
index d918cb1d83a6..012cffc574e8 100644
--- a/arch/arm64/include/asm/page.h
+++ b/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>

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index f9401a3205a8..78a545536a45 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -671,8 +671,13 @@ 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);
diff --git a/arch/arm64/include/uapi/asm/mman.h b/arch/arm64/include/uapi/asm/mman.h
index 6fdd71eb644f..1e6482a838e1 100644
--- a/arch/arm64/include/uapi/asm/mman.h
+++ b/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 */
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index dbda4499a859..4f8ae353a8c5 100644
--- a/fs/proc/task_mmu.c
+++ b/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)] = "",
diff --git a/include/linux/mm.h b/include/linux/mm.h
index dc7b87310c10..65cbbfaa739b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -333,6 +333,14 @@ 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