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arm64: kasan: mte: use a constant kernel GCR_EL1 value

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When KASAN_HW_TAGS is selected, KASAN is enabled at boot time, and the
hardware supports MTE, we'll initialize `kernel_gcr_excl` with a value
dependent on KASAN_TAG_MAX. While the resulting value is a constant
which depends on KASAN_TAG_MAX, we have to perform some runtime work to
generate the value, and have to read the value from memory during the
exception entry path. It would be better if we could generate this as a
constant at compile-time, and use it as such directly.

Early in boot within __cpu_setup(), we initialize GCR_EL1 to a safe
value, and later override this with the value required by KASAN. If
CONFIG_KASAN_HW_TAGS is not selected, or if KASAN is disabeld at boot
time, the kernel will not use IRG instructions, and so the initial value
of GCR_EL1 is does not matter to the kernel. Thus, we can instead have
__cpu_setup() initialize GCR_EL1 to a value consistent with
KASAN_TAG_MAX, and avoid the need to re-initialize it during hotplug and
resume form suspend.

This patch makes arem64 use a compile-time constant KERNEL_GCR_EL1
value, which is compatible with KASAN_HW_TAGS when this is selected.
This removes the need to re-initialize GCR_EL1 dynamically, and acts as
an optimization to the entry assembly, which no longer needs to load
this value from memory. The redundant initialization hooks are removed.

In order to do this, KASAN_TAG_MAX needs to be visible outside of the
core KASAN code. To do this, I've moved the KASAN_TAG_* values into
<linux/kasan-tags.h>.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Tested-by: Andrey Konovalov <andreyknvl@gmail.com>
Link: https://lore.kernel.org/r/20210714143843.56537-3-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Mark Rutland 2021-07-14 15:38:42 +01:00 committed by Catalin Marinas
parent d914b80a8f
commit 8286824789
11 changed files with 35 additions and 65 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/arm64/include/asm/memory.h
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@ -245,7 +245,6 @@ static inline const void *__tag_set(const void *addr, u8 tag)
#define arch_enable_tagging_async() mte_enable_kernel_async()
#define arch_set_tagging_report_once(state) mte_set_report_once(state)
#define arch_force_async_tag_fault() mte_check_tfsr_exit()
#define arch_init_tags(max_tag) mte_init_tags(max_tag)
#define arch_get_random_tag() mte_get_random_tag()
#define arch_get_mem_tag(addr) mte_get_mem_tag(addr)
#define arch_set_mem_tag_range(addr, size, tag, init) \

5
arch/arm64/include/asm/mte-kasan.h
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@ -130,7 +130,6 @@ static inline void mte_set_mem_tag_range(void *addr, size_t size, u8 tag,
void mte_enable_kernel_sync(void);
void mte_enable_kernel_async(void);
void mte_init_tags(u64 max_tag);
void mte_set_report_once(bool state);
bool mte_report_once(void);
@ -165,10 +164,6 @@ static inline void mte_enable_kernel_async(void)
{
}
static inline void mte_init_tags(u64 max_tag)
{
}
static inline void mte_set_report_once(bool state)
{
}

6
arch/arm64/include/asm/mte.h
View File

@ -16,8 +16,6 @@
#include <asm/pgtable-types.h>
extern u64 gcr_kernel_excl;
void mte_clear_page_tags(void *addr);
unsigned long mte_copy_tags_from_user(void *to, const void __user *from,
unsigned long n);
@ -43,7 +41,6 @@ void mte_copy_page_tags(void *kto, const void *kfrom);
void mte_thread_init_user(void);
void mte_thread_switch(struct task_struct *next);
void mte_suspend_enter(void);
void mte_suspend_exit(void);
long set_mte_ctrl(struct task_struct *task, unsigned long arg);
long get_mte_ctrl(struct task_struct *task);
int mte_ptrace_copy_tags(struct task_struct *child, long request,
@ -72,9 +69,6 @@ static inline void mte_thread_switch(struct task_struct *next)
static inline void mte_suspend_enter(void)
{
}
static inline void mte_suspend_exit(void)
{
}
static inline long set_mte_ctrl(struct task_struct *task, unsigned long arg)
{
return 0;

16
arch/arm64/include/asm/sysreg.h
View File

@ -11,6 +11,7 @@
#include <linux/bits.h>
#include <linux/stringify.h>
#include <linux/kasan-tags.h>
/*
* ARMv8 ARM reserves the following encoding for system registers:
@ -1067,6 +1068,21 @@
#define SYS_GCR_EL1_RRND (BIT(16))
#define SYS_GCR_EL1_EXCL_MASK 0xffffUL
#ifdef CONFIG_KASAN_HW_TAGS
/*
* KASAN always uses a whole byte for its tags. With CONFIG_KASAN_HW_TAGS it
* only uses tags in the range 0xF0-0xFF, which we map to MTE tags 0x0-0xF.
*/
#define __MTE_TAG_MIN (KASAN_TAG_MIN & 0xf)
#define __MTE_TAG_MAX (KASAN_TAG_MAX & 0xf)
#define __MTE_TAG_INCL GENMASK(__MTE_TAG_MAX, __MTE_TAG_MIN)
#define KERNEL_GCR_EL1_EXCL (SYS_GCR_EL1_EXCL_MASK & ~__MTE_TAG_INCL)
#else
#define KERNEL_GCR_EL1_EXCL SYS_GCR_EL1_EXCL_MASK
#endif
#define KERNEL_GCR_EL1 (SYS_GCR_EL1_RRND | KERNEL_GCR_EL1_EXCL)
/* RGSR_EL1 Definitions */
#define SYS_RGSR_EL1_TAG_MASK 0xfUL
#define SYS_RGSR_EL1_SEED_SHIFT 8

5
arch/arm64/kernel/entry.S
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@ -181,9 +181,8 @@ alternative_else_nop_endif
alternative_if_not ARM64_MTE
b 1f
alternative_else_nop_endif
ldr_l \tmp, gcr_kernel_excl
mte_set_gcr \tmp, \tmp2
mov \tmp, KERNEL_GCR_EL1
msr_s SYS_GCR_EL1, \tmp
1:
#endif
.endm

31
arch/arm64/kernel/mte.c
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@ -23,8 +23,6 @@
#include <asm/ptrace.h>
#include <asm/sysreg.h>
u64 gcr_kernel_excl __ro_after_init;
static bool report_fault_once = true;
static DEFINE_PER_CPU_READ_MOSTLY(u64, mte_tcf_preferred);
@ -104,26 +102,6 @@ int memcmp_pages(struct page *page1, struct page *page2)
return ret;
}
void mte_init_tags(u64 max_tag)
{
static bool gcr_kernel_excl_initialized;
if (!gcr_kernel_excl_initialized) {
/*
* The format of the tags in KASAN is 0xFF and in MTE is 0xF.
* This conversion extracts an MTE tag from a KASAN tag.
*/
u64 incl = GENMASK(FIELD_GET(MTE_TAG_MASK >> MTE_TAG_SHIFT,
max_tag), 0);
gcr_kernel_excl = ~incl & SYS_GCR_EL1_EXCL_MASK;
gcr_kernel_excl_initialized = true;
}
/* Enable the kernel exclude mask for random tags generation. */
write_sysreg_s(SYS_GCR_EL1_RRND | gcr_kernel_excl, SYS_GCR_EL1);
}
static inline void __mte_enable_kernel(const char *mode, unsigned long tcf)
{
/* Enable MTE Sync Mode for EL1. */
@ -262,15 +240,6 @@ void mte_suspend_enter(void)
mte_check_tfsr_el1();
}
void mte_suspend_exit(void)
{
if (!system_supports_mte())
return;
sysreg_clear_set_s(SYS_GCR_EL1, SYS_GCR_EL1_EXCL_MASK, gcr_kernel_excl);
isb();
}
long set_mte_ctrl(struct task_struct *task, unsigned long arg)
{
u64 mte_ctrl = (~((arg & PR_MTE_TAG_MASK) >> PR_MTE_TAG_SHIFT) &

1
arch/arm64/kernel/suspend.c
View File

@ -76,7 +76,6 @@ void notrace __cpu_suspend_exit(void)
spectre_v4_enable_mitigation(NULL);
/* Restore additional feature-specific configuration */
mte_suspend_exit();
ptrauth_suspend_exit();
}

3
arch/arm64/mm/proc.S
View File

@ -437,8 +437,7 @@ SYM_FUNC_START(__cpu_setup)
mov x10, #MAIR_ATTR_NORMAL_TAGGED
bfi mair, x10, #(8 * MT_NORMAL_TAGGED), #8
/* initialize GCR_EL1: all non-zero tags excluded by default */
mov x10, #(SYS_GCR_EL1_RRND | SYS_GCR_EL1_EXCL_MASK)
mov x10, #KERNEL_GCR_EL1
msr_s SYS_GCR_EL1, x10
/*

15
include/linux/kasan-tags.h Normal file
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@ -0,0 +1,15 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_KASAN_TAGS_H
#define _LINUX_KASAN_TAGS_H
#define KASAN_TAG_KERNEL 0xFF /* native kernel pointers tag */
#define KASAN_TAG_INVALID 0xFE /* inaccessible memory tag */
#define KASAN_TAG_MAX 0xFD /* maximum value for random tags */
#ifdef CONFIG_KASAN_HW_TAGS
#define KASAN_TAG_MIN 0xF0 /* minimum value for random tags */
#else
#define KASAN_TAG_MIN 0x00 /* minimum value for random tags */
#endif
#endif /* LINUX_KASAN_TAGS_H */

2
mm/kasan/hw_tags.c
View File

@ -142,8 +142,6 @@ void kasan_init_hw_tags_cpu(void)
if (kasan_arg == KASAN_ARG_OFF)
return;
hw_init_tags(KASAN_TAG_MAX);
/*
* Enable async mode only when explicitly requested through
* the command line.

15
mm/kasan/kasan.h
View File

@ -3,6 +3,7 @@
#define __MM_KASAN_KASAN_H
#include <linux/kasan.h>
#include <linux/kasan-tags.h>
#include <linux/kfence.h>
#include <linux/stackdepot.h>
@ -51,16 +52,6 @@ extern bool kasan_flag_async __ro_after_init;
#define KASAN_MEMORY_PER_SHADOW_PAGE (KASAN_GRANULE_SIZE << PAGE_SHIFT)
#define KASAN_TAG_KERNEL 0xFF /* native kernel pointers tag */
#define KASAN_TAG_INVALID 0xFE /* inaccessible memory tag */
#define KASAN_TAG_MAX 0xFD /* maximum value for random tags */
#ifdef CONFIG_KASAN_HW_TAGS
#define KASAN_TAG_MIN 0xF0 /* minimum value for random tags */
#else
#define KASAN_TAG_MIN 0x00 /* minimum value for random tags */
#endif
#ifdef CONFIG_KASAN_GENERIC
#define KASAN_FREE_PAGE 0xFF /* page was freed */
#define KASAN_PAGE_REDZONE 0xFE /* redzone for kmalloc_large allocations */
@ -299,9 +290,6 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
#ifndef arch_enable_tagging_async
#define arch_enable_tagging_async()
#endif
#ifndef arch_init_tags
#define arch_init_tags(max_tag)
#endif
#ifndef arch_set_tagging_report_once
#define arch_set_tagging_report_once(state)
#endif
@ -320,7 +308,6 @@ static inline const void *arch_kasan_set_tag(const void *addr, u8 tag)
#define hw_enable_tagging_sync() arch_enable_tagging_sync()
#define hw_enable_tagging_async() arch_enable_tagging_async()
#define hw_init_tags(max_tag) arch_init_tags(max_tag)
#define hw_set_tagging_report_once(state) arch_set_tagging_report_once(state)
#define hw_force_async_tag_fault() arch_force_async_tag_fault()
#define hw_get_random_tag() arch_get_random_tag()