Commit 9f341931 authored by Catalin Marinas's avatar Catalin Marinas
Browse files

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: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: default avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
parent b3fbbea4

arch/arm64/include/asm/memory.h

+11 −7
Original line number Diff line number Diff line
@@ -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

+41 −3
Original line number Diff line number Diff line
@@ -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

+1 −1
Original line number Diff line number Diff line
@@ -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

+6 −1
Original line number Diff line number Diff line
@@ -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

+1 −0
Original line number Diff line number Diff line
@@ -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 */

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