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arm64: mte: add in-kernel MTE helpers
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Provide helper functions to manipulate allocation and pointer tags for
kernel addresses.

Low-level helper functions (mte_assign_*, written in assembly) operate tag
values from the [0x0, 0xF] range.  High-level helper functions
(mte_get/set_*) use the [0xF0, 0xFF] range to preserve compatibility with
normal kernel pointers that have 0xFF in their top byte.

MTE_GRANULE_SIZE and related definitions are moved to mte-def.h header
that doesn't have any dependencies and is safe to include into any
low-level header.

Link: https://lkml.kernel.org/r/c31bf759b4411b2d98cdd801eb928e241584fd1f.1606161801.git.andreyknvl@google.com
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Co-developed-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Marco Elver <elver@google.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Vincenzo Frascino authored and Linus Torvalds committed Dec 22, 2020
1 parent f469c03 commit 85f49ca
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Showing 6 changed files with 150 additions and 6 deletions.
1 change: 1 addition & 0 deletions arch/arm64/include/asm/esr.h
Original file line number Diff line number Diff line change
Expand Up @@ -106,6 +106,7 @@
#define ESR_ELx_FSC_TYPE (0x3C)
#define ESR_ELx_FSC_LEVEL (0x03)
#define ESR_ELx_FSC_EXTABT (0x10)
#define ESR_ELx_FSC_MTE (0x11)
#define ESR_ELx_FSC_SERROR (0x11)
#define ESR_ELx_FSC_ACCESS (0x08)
#define ESR_ELx_FSC_FAULT (0x04)
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15 changes: 15 additions & 0 deletions arch/arm64/include/asm/mte-def.h
Original file line number Diff line number Diff line change
@@ -0,0 +1,15 @@
/* SPDX-License-Identifier: GPL-2.0 */
/*
* Copyright (C) 2020 ARM Ltd.
*/
#ifndef __ASM_MTE_DEF_H
#define __ASM_MTE_DEF_H

#define MTE_GRANULE_SIZE UL(16)
#define MTE_GRANULE_MASK (~(MTE_GRANULE_SIZE - 1))
#define MTE_TAG_SHIFT 56
#define MTE_TAG_SIZE 4
#define MTE_TAG_MASK GENMASK((MTE_TAG_SHIFT + (MTE_TAG_SIZE - 1)), MTE_TAG_SHIFT)
#define MTE_TAG_MAX (MTE_TAG_MASK >> MTE_TAG_SHIFT)

#endif /* __ASM_MTE_DEF_H */
56 changes: 56 additions & 0 deletions arch/arm64/include/asm/mte-kasan.h
Original file line number Diff line number Diff line change
@@ -0,0 +1,56 @@
/* SPDX-License-Identifier: GPL-2.0 */
/*
* Copyright (C) 2020 ARM Ltd.
*/
#ifndef __ASM_MTE_KASAN_H
#define __ASM_MTE_KASAN_H

#include <asm/mte-def.h>

#ifndef __ASSEMBLY__

#include <linux/types.h>

/*
* The functions below are meant to be used only for the
* KASAN_HW_TAGS interface defined in asm/memory.h.
*/
#ifdef CONFIG_ARM64_MTE

static inline u8 mte_get_ptr_tag(void *ptr)
{
/* Note: The format of KASAN tags is 0xF<x> */
u8 tag = 0xF0 | (u8)(((u64)(ptr)) >> MTE_TAG_SHIFT);

return tag;
}

u8 mte_get_mem_tag(void *addr);
u8 mte_get_random_tag(void);
void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag);

#else /* CONFIG_ARM64_MTE */

static inline u8 mte_get_ptr_tag(void *ptr)
{
return 0xFF;
}

static inline u8 mte_get_mem_tag(void *addr)
{
return 0xFF;
}
static inline u8 mte_get_random_tag(void)
{
return 0xFF;
}
static inline void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
{
return addr;
}

#endif /* CONFIG_ARM64_MTE */

#endif /* __ASSEMBLY__ */

#endif /* __ASM_MTE_KASAN_H */
20 changes: 14 additions & 6 deletions arch/arm64/include/asm/mte.h
Original file line number Diff line number Diff line change
Expand Up @@ -5,14 +5,16 @@
#ifndef __ASM_MTE_H
#define __ASM_MTE_H

#define MTE_GRANULE_SIZE UL(16)
#define MTE_GRANULE_MASK (~(MTE_GRANULE_SIZE - 1))
#define MTE_TAG_SHIFT 56
#define MTE_TAG_SIZE 4
#include <asm/compiler.h>
#include <asm/mte-def.h>

#define __MTE_PREAMBLE ARM64_ASM_PREAMBLE ".arch_extension memtag\n"

#ifndef __ASSEMBLY__

#include <linux/bitfield.h>
#include <linux/page-flags.h>
#include <linux/types.h>

#include <asm/pgtable-types.h>

Expand Down Expand Up @@ -45,7 +47,9 @@ long get_mte_ctrl(struct task_struct *task);
int mte_ptrace_copy_tags(struct task_struct *child, long request,
unsigned long addr, unsigned long data);

#else
void mte_assign_mem_tag_range(void *addr, size_t size);

#else /* CONFIG_ARM64_MTE */

/* unused if !CONFIG_ARM64_MTE, silence the compiler */
#define PG_mte_tagged 0
Expand Down Expand Up @@ -80,7 +84,11 @@ static inline int mte_ptrace_copy_tags(struct task_struct *child,
return -EIO;
}

#endif
static inline void mte_assign_mem_tag_range(void *addr, size_t size)
{
}

#endif /* CONFIG_ARM64_MTE */

#endif /* __ASSEMBLY__ */
#endif /* __ASM_MTE_H */
48 changes: 48 additions & 0 deletions arch/arm64/kernel/mte.c
Original file line number Diff line number Diff line change
Expand Up @@ -13,10 +13,13 @@
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/thread_info.h>
#include <linux/types.h>
#include <linux/uio.h>

#include <asm/barrier.h>
#include <asm/cpufeature.h>
#include <asm/mte.h>
#include <asm/mte-kasan.h>
#include <asm/ptrace.h>
#include <asm/sysreg.h>

Expand Down Expand Up @@ -72,6 +75,51 @@ int memcmp_pages(struct page *page1, struct page *page2)
return ret;
}

u8 mte_get_mem_tag(void *addr)
{
if (!system_supports_mte())
return 0xFF;

asm(__MTE_PREAMBLE "ldg %0, [%0]"
: "+r" (addr));

return mte_get_ptr_tag(addr);
}

u8 mte_get_random_tag(void)
{
void *addr;

if (!system_supports_mte())
return 0xFF;

asm(__MTE_PREAMBLE "irg %0, %0"
: "+r" (addr));

return mte_get_ptr_tag(addr);
}

void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
{
void *ptr = addr;

if ((!system_supports_mte()) || (size == 0))
return addr;

/* Make sure that size is MTE granule aligned. */
WARN_ON(size & (MTE_GRANULE_SIZE - 1));

/* Make sure that the address is MTE granule aligned. */
WARN_ON((u64)addr & (MTE_GRANULE_SIZE - 1));

tag = 0xF0 | tag;
ptr = (void *)__tag_set(ptr, tag);

mte_assign_mem_tag_range(ptr, size);

return ptr;
}

static void update_sctlr_el1_tcf0(u64 tcf0)
{
/* ISB required for the kernel uaccess routines */
Expand Down
16 changes: 16 additions & 0 deletions arch/arm64/lib/mte.S
Original file line number Diff line number Diff line change
Expand Up @@ -149,3 +149,19 @@ SYM_FUNC_START(mte_restore_page_tags)

ret
SYM_FUNC_END(mte_restore_page_tags)

/*
* Assign allocation tags for a region of memory based on the pointer tag
* x0 - source pointer
* x1 - size
*
* Note: The address must be non-NULL and MTE_GRANULE_SIZE aligned and
* size must be non-zero and MTE_GRANULE_SIZE aligned.
*/
SYM_FUNC_START(mte_assign_mem_tag_range)
1: stg x0, [x0]
add x0, x0, #MTE_GRANULE_SIZE
subs x1, x1, #MTE_GRANULE_SIZE
b.gt 1b
ret
SYM_FUNC_END(mte_assign_mem_tag_range)

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