Pages allocated by the kernel are not guaranteed to have the tags
zeroed, especially as the kernel does not (yet) use MTE itself. To
ensure the user can still access such pages when mapped into its address
space, clear the tags via set_pte_at(). A new page flag - PG_mte_tagged
(PG_arch_2) - is used to track pages with valid allocation tags.
Since the zero page is mapped as pte_special(), it won't be covered by
the above set_pte_at() mechanism. Clear its tags during early MTE
initialisation.
Co-developed-by: Steven Price <steven.price@xxxxxxx>
Signed-off-by: Steven Price <steven.price@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
---
Notes:
v8:
- Introduce the cpu_enable_mte() function in this patch as it was no
longer present in the previous ones.
v5:
- Fix the handling of compound pages. Previously, set_pte_at() could
have erased already valid tags if the first page in a compound one
did not have the PG_mte_tagged flag set.
- Move the multi_tag_transfer_size macro from assembler.h to mte.S.
- Ignore pte_special() mappings and clear the tags in the zero page
separately (since it's mapped as a special pte).
- Clearing the tags of the zero page was moved to this patch from an
earlier one since mte_clear_page_tags() was not available.
New in v4. Replacing a previous page zeroing the tags in clear_page().
arch/arm64/include/asm/mte.h | 16 +++++++++++++++
arch/arm64/include/asm/pgtable.h | 7 +++++++
arch/arm64/kernel/cpufeature.c | 18 +++++++++++++++++
arch/arm64/kernel/mte.c | 14 +++++++++++++
arch/arm64/lib/Makefile | 2 ++
arch/arm64/lib/mte.S | 34 ++++++++++++++++++++++++++++++++
6 files changed, 91 insertions(+)
create mode 100644 arch/arm64/lib/mte.S
diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index a0bf310da74b..1716b3d02489 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -7,12 +7,28 @@
#ifndef __ASSEMBLY__
+#include <linux/page-flags.h>
+
+#include <asm/pgtable-types.h>
+
+void mte_clear_page_tags(void *addr);
+
#ifdef CONFIG_ARM64_MTE
+/* track which pages have valid allocation tags */
+#define PG_mte_tagged PG_arch_2
+
+void mte_sync_tags(pte_t *ptep, pte_t pte);
void flush_mte_state(void);
#else
+/* unused if !CONFIG_ARM64_MTE, silence the compiler */
+#define PG_mte_tagged 0
+
+static inline void mte_sync_tags(pte_t *ptep, pte_t pte)
+{
+}
static inline void flush_mte_state(void)
{
}
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index d5d3fbe73953..0a205a8e91b2 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -9,6 +9,7 @@
#include <asm/proc-fns.h>
#include <asm/memory.h>
+#include <asm/mte.h>
#include <asm/pgtable-hwdef.h>
#include <asm/pgtable-prot.h>
#include <asm/tlbflush.h>
@@ -90,6 +91,8 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
#define pte_user_exec(pte) (!(pte_val(pte) & PTE_UXN))
#define pte_cont(pte) (!!(pte_val(pte) & PTE_CONT))
#define pte_devmap(pte) (!!(pte_val(pte) & PTE_DEVMAP))
+#define pte_tagged(pte) ((pte_val(pte) & PTE_ATTRINDX_MASK) == \
+ PTE_ATTRINDX(MT_NORMAL_TAGGED))
#define pte_cont_addr_end(addr, end) \
({ unsigned long __boundary = ((addr) + CONT_PTE_SIZE) & CONT_PTE_MASK; \
@@ -284,6 +287,10 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
if (pte_present(pte) && pte_user_exec(pte) && !pte_special(pte))
__sync_icache_dcache(pte);
+ if (system_supports_mte() &&
+ pte_present(pte) && pte_tagged(pte) && !pte_special(pte))
+ mte_sync_tags(ptep, pte);
+
__check_racy_pte_update(mm, ptep, pte);
set_pte(ptep, pte);
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 00cdf8c2e8c1..36c12439c2af 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -75,6 +75,7 @@
#include <asm/cpu_ops.h>
#include <asm/fpsimd.h>
#include <asm/mmu_context.h>
+#include <asm/mte.h>
#include <asm/processor.h>
#include <asm/sysreg.h>
#include <asm/traps.h>
@@ -1704,6 +1705,22 @@ static void bti_enable(const struct arm64_cpu_capabilities *__unused)
}
#endif /* CONFIG_ARM64_BTI */
+#ifdef CONFIG_ARM64_MTE
+static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap)
+{
+ static bool cleared_zero_page = false;
+
+ /*
+ * Clear the tags in the zero page. This needs to be done via the
+ * linear map which has the Tagged attribute.
+ */
+ if (!cleared_zero_page) {
+ cleared_zero_page = true;
+ mte_clear_page_tags(lm_alias(empty_zero_page));
+ }
+}
+#endif /* CONFIG_ARM64_MTE */
+
/* Internal helper functions to match cpu capability type */
static bool
cpucap_late_cpu_optional(const struct arm64_cpu_capabilities *cap)
@@ -2133,6 +2150,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.field_pos = ID_AA64PFR1_MTE_SHIFT,
.min_field_value = ID_AA64PFR1_MTE,
.sign = FTR_UNSIGNED,
+ .cpu_enable = cpu_enable_mte,
},
#endif /* CONFIG_ARM64_MTE */
{},
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 032016823957..5bf9bbed5a25 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -3,12 +3,26 @@
* Copyright (C) 2020 ARM Ltd.
*/
+#include <linux/bitops.h>
+#include <linux/mm.h>
#include <linux/thread_info.h>
#include <asm/cpufeature.h>
#include <asm/mte.h>
#include <asm/sysreg.h>
+void mte_sync_tags(pte_t *ptep, pte_t pte)
+{
+ struct page *page = pte_page(pte);
+ long i, nr_pages = compound_nr(page);
+
+ /* if PG_mte_tagged is set, tags have already been initialised */
+ for (i = 0; i < nr_pages; i++, page++) {
+ if (!test_and_set_bit(PG_mte_tagged, &page->flags))
+ mte_clear_page_tags(page_address(page));
+ }
+}
+
void flush_mte_state(void)
{
if (!system_supports_mte())
diff --git a/arch/arm64/lib/Makefile b/arch/arm64/lib/Makefile
index 2fc253466dbf..d31e1169d9b8 100644
--- a/arch/arm64/lib/Makefile
+++ b/arch/arm64/lib/Makefile
@@ -16,3 +16,5 @@ lib-$(CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE) += uaccess_flushcache.o
obj-$(CONFIG_CRC32) += crc32.o
obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
+
+obj-$(CONFIG_ARM64_MTE) += mte.o
diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S
new file mode 100644
index 000000000000..a36705640086
--- /dev/null
+++ b/arch/arm64/lib/mte.S
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 ARM Ltd.
+ */
+#include <linux/linkage.h>
+
+#include <asm/assembler.h>
+#include <asm/sysreg.h>
+
+ .arch armv8.5-a+memtag
+
+/*
+ * multitag_transfer_size - set \reg to the block size that is accessed by the
+ * LDGM/STGM instructions.
+ */
+ .macro multitag_transfer_size, reg, tmp
+ mrs_s \reg, SYS_GMID_EL1
+ ubfx \reg, \reg, #SYS_GMID_EL1_BS_SHIFT, #SYS_GMID_EL1_BS_SIZE
+ mov \tmp, #4
+ lsl \reg, \tmp, \reg
+ .endm
+
+/*
+ * Clear the tags in a page
+ * x0 - address of the page to be cleared
+ */
+SYM_FUNC_START(mte_clear_page_tags)
+ multitag_transfer_size x1, x2
+1: stgm xzr, [x0]
+ add x0, x0, x1
+ tst x0, #(PAGE_SIZE - 1)
+ b.ne 1b
+ ret
+SYM_FUNC_END(mte_clear_page_tags)
