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Date: Wed, 6 Oct 2021 16:47:50 +0100
From: Vincenzo Frascino <vincenzo.frascino@....com>
To: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
kasan-dev@...glegroups.com
Cc: vincenzo.frascino@....com,
Andrew Morton <akpm@...ux-foundation.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Dmitry Vyukov <dvyukov@...gle.com>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Alexander Potapenko <glider@...gle.com>,
Marco Elver <elver@...gle.com>,
Evgenii Stepanov <eugenis@...gle.com>,
Branislav Rankov <Branislav.Rankov@....com>,
Andrey Konovalov <andreyknvl@...il.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Subject: [PATCH v3 4/5] arm64: mte: Add asymmetric mode support
MTE provides an asymmetric mode for detecting tag exceptions. In
particular, when such a mode is present, the CPU triggers a fault
on a tag mismatch during a load operation and asynchronously updates
a register when a tag mismatch is detected during a store operation.
Add support for MTE asymmetric mode.
Note: If the CPU does not support MTE asymmetric mode the kernel falls
back on synchronous mode which is the default for kasan=on.
Cc: Will Deacon <will@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Andrey Konovalov <andreyknvl@...il.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
---
arch/arm64/include/asm/memory.h | 1 +
arch/arm64/include/asm/mte-kasan.h | 5 ++++
arch/arm64/include/asm/mte.h | 8 +++---
arch/arm64/include/asm/uaccess.h | 4 +--
arch/arm64/kernel/mte.c | 43 +++++++++++++++++++++++++-----
5 files changed, 49 insertions(+), 12 deletions(-)
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index f1745a843414..1b9a1e242612 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -243,6 +243,7 @@ static inline const void *__tag_set(const void *addr, u8 tag)
#ifdef CONFIG_KASAN_HW_TAGS
#define arch_enable_tagging_sync() mte_enable_kernel_sync()
#define arch_enable_tagging_async() mte_enable_kernel_async()
+#define arch_enable_tagging_asymm() mte_enable_kernel_asymm()
#define arch_force_async_tag_fault() mte_check_tfsr_exit()
#define arch_get_random_tag() mte_get_random_tag()
#define arch_get_mem_tag(addr) mte_get_mem_tag(addr)
diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
index 22420e1f8c03..478b9bcf69ad 100644
--- a/arch/arm64/include/asm/mte-kasan.h
+++ b/arch/arm64/include/asm/mte-kasan.h
@@ -130,6 +130,7 @@ 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_enable_kernel_asymm(void);
#else /* CONFIG_ARM64_MTE */
@@ -161,6 +162,10 @@ static inline void mte_enable_kernel_async(void)
{
}
+static inline void mte_enable_kernel_asymm(void)
+{
+}
+
#endif /* CONFIG_ARM64_MTE */
#endif /* __ASSEMBLY__ */
diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index 02511650cffe..075539f5f1c8 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -88,11 +88,11 @@ static inline int mte_ptrace_copy_tags(struct task_struct *child,
#ifdef CONFIG_KASAN_HW_TAGS
/* Whether the MTE asynchronous mode is enabled. */
-DECLARE_STATIC_KEY_FALSE(mte_async_mode);
+DECLARE_STATIC_KEY_FALSE(mte_async_or_asymm_mode);
-static inline bool system_uses_mte_async_mode(void)
+static inline bool system_uses_mte_async_or_asymm_mode(void)
{
- return static_branch_unlikely(&mte_async_mode);
+ return static_branch_unlikely(&mte_async_or_asymm_mode);
}
void mte_check_tfsr_el1(void);
@@ -121,7 +121,7 @@ static inline void mte_check_tfsr_exit(void)
mte_check_tfsr_el1();
}
#else
-static inline bool system_uses_mte_async_mode(void)
+static inline bool system_uses_mte_async_or_asymm_mode(void)
{
return false;
}
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 190b494e22ab..315354047d69 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -196,13 +196,13 @@ static inline void __uaccess_enable_tco(void)
*/
static inline void __uaccess_disable_tco_async(void)
{
- if (system_uses_mte_async_mode())
+ if (system_uses_mte_async_or_asymm_mode())
__uaccess_disable_tco();
}
static inline void __uaccess_enable_tco_async(void)
{
- if (system_uses_mte_async_mode())
+ if (system_uses_mte_async_or_asymm_mode())
__uaccess_enable_tco();
}
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index e5e801bc5312..d7da4e3924c4 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -26,9 +26,14 @@
static DEFINE_PER_CPU_READ_MOSTLY(u64, mte_tcf_preferred);
#ifdef CONFIG_KASAN_HW_TAGS
-/* Whether the MTE asynchronous mode is enabled. */
-DEFINE_STATIC_KEY_FALSE(mte_async_mode);
-EXPORT_SYMBOL_GPL(mte_async_mode);
+/*
+ * The MTE asynchronous and asymmetric mode have the same
+ * behavior for the store operations.
+ *
+ * Whether the MTE asynchronous or asymmetric mode is enabled.
+ */
+DEFINE_STATIC_KEY_FALSE(mte_async_or_asymm_mode);
+EXPORT_SYMBOL_GPL(mte_async_or_asymm_mode);
#endif
static void mte_sync_page_tags(struct page *page, pte_t old_pte,
@@ -116,7 +121,7 @@ void mte_enable_kernel_sync(void)
* Make sure we enter this function when no PE has set
* async mode previously.
*/
- WARN_ONCE(system_uses_mte_async_mode(),
+ WARN_ONCE(system_uses_mte_async_or_asymm_mode(),
"MTE async mode enabled system wide!");
__mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC);
@@ -134,8 +139,34 @@ void mte_enable_kernel_async(void)
* mode in between sync and async, this strategy needs
* to be reviewed.
*/
- if (!system_uses_mte_async_mode())
- static_branch_enable(&mte_async_mode);
+ if (!system_uses_mte_async_or_asymm_mode())
+ static_branch_enable(&mte_async_or_asymm_mode);
+}
+
+void mte_enable_kernel_asymm(void)
+{
+ if (cpus_have_cap(ARM64_MTE_ASYMM)) {
+ __mte_enable_kernel("asymmetric", SCTLR_ELx_TCF_ASYMM);
+
+ /*
+ * MTE asymm mode behaves as async mode for store
+ * operations. The mode is set system wide by the
+ * first PE that executes this function.
+ *
+ * Note: If in future KASAN acquires a runtime switching
+ * mode in between sync and async, this strategy needs
+ * to be reviewed.
+ */
+ if (!system_uses_mte_async_or_asymm_mode())
+ static_branch_enable(&mte_async_or_asymm_mode);
+ } else {
+ /*
+ * If the CPU does not support MTE asymmetric mode the
+ * kernel falls back on synchronous mode which is the
+ * default for kasan=on.
+ */
+ mte_enable_kernel_sync();
+ }
}
#endif
--
2.33.0
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