[PATCH v8 30/43] arm64: kasan: Allow enabling in-kernel MTE

Andrey Konovalov
2020-11-04T23:20:26Z

Hardware tag-based KASAN relies on Memory Tagging Extension (MTE)
feature and requires it to be enabled. MTE supports

This patch adds a new mte_init_tags() helper, that enables MTE in
Synchronous mode in EL1 and is intended to be called from KASAN runtime
during initialization.

The Tag Checking operation causes a synchronous data abort as
a consequence of a tag check fault when MTE is configured in
synchronous mode.

As part of this change enable match-all tag for EL1 to allow the
kernel to access user pages without faulting. This is required because
the kernel does not have knowledge of the tags set by the user in a
page.

Note: For MTE, the TCF bit field in SCTLR_EL1 affects only EL1 in a
similar way as TCF0 affects EL0.

MTE that is built on top of the Top Byte Ignore (TBI) feature hence we
enable it as part of this patch as well.

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>
---
Change-Id: I4d67497268bb7f0c2fc5dcacefa1e273df4af71d
---
arch/arm64/include/asm/mte-kasan.h | 6 ++++++
arch/arm64/kernel/mte.c | 7 +++++++
arch/arm64/mm/proc.S | 23 ++++++++++++++++++++---
3 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
index 3a70fb1807fd..ae75feaea2d4 100644
--- a/arch/arm64/include/asm/mte-kasan.h
+++ b/arch/arm64/include/asm/mte-kasan.h
@@ -29,6 +29,8 @@ 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);

+void __init mte_init_tags(u64 max_tag);
+
#else /* CONFIG_ARM64_MTE */

static inline u8 mte_get_ptr_tag(void *ptr)
@@ -49,6 +51,10 @@ static inline void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
return addr;
}

+static inline void mte_init_tags(u64 max_tag)
+{
+}
+
#endif /* CONFIG_ARM64_MTE */

#endif /* __ASSEMBLY__ */
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 06ba6c923ab7..fcfbefcc3174 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -121,6 +121,13 @@ void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
return ptr;
}

+void __init mte_init_tags(u64 max_tag)
+{
+ /* Enable MTE Sync Mode for EL1. */
+ sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
+ isb();
+}
+
static void update_sctlr_el1_tcf0(u64 tcf0)
{
/* ISB required for the kernel uaccess routines */
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 23c326a06b2d..7c3304fb15d9 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -40,9 +40,15 @@
#define TCR_CACHE_FLAGS TCR_IRGN_WBWA | TCR_ORGN_WBWA

#ifdef CONFIG_KASAN_SW_TAGS
-#define TCR_KASAN_FLAGS TCR_TBI1
+#define TCR_KASAN_SW_FLAGS TCR_TBI1
#else
-#define TCR_KASAN_FLAGS 0
+#define TCR_KASAN_SW_FLAGS 0
+#endif
+
+#ifdef CONFIG_KASAN_HW_TAGS
+#define TCR_KASAN_HW_FLAGS SYS_TCR_EL1_TCMA1 | TCR_TBI1
+#else
+#define TCR_KASAN_HW_FLAGS 0
#endif

/*
@@ -427,6 +433,10 @@ SYM_FUNC_START(__cpu_setup)
*/
mov_q x5, MAIR_EL1_SET
#ifdef CONFIG_ARM64_MTE
+ mte_tcr .req x20
+
+ mov mte_tcr, #0
+
/*
* Update MAIR_EL1, GCR_EL1 and TFSR*_EL1 if MTE is supported
* (ID_AA64PFR1_EL1[11:8] > 1).
@@ -447,6 +457,9 @@ SYM_FUNC_START(__cpu_setup)
/* clear any pending tag check faults in TFSR*_EL1 */
msr_s SYS_TFSR_EL1, xzr
msr_s SYS_TFSRE0_EL1, xzr
+
+ /* set the TCR_EL1 bits */
+ mov_q mte_tcr, TCR_KASAN_HW_FLAGS
1:
#endif
msr mair_el1, x5
@@ -456,7 +469,11 @@ SYM_FUNC_START(__cpu_setup)
*/
mov_q x10, TCR_TxSZ(VA_BITS) | TCR_CACHE_FLAGS | TCR_SMP_FLAGS | \
TCR_TG_FLAGS | TCR_KASLR_FLAGS | TCR_ASID16 | \
- TCR_TBI0 | TCR_A1 | TCR_KASAN_FLAGS
+ TCR_TBI0 | TCR_A1 | TCR_KASAN_SW_FLAGS
+#ifdef CONFIG_ARM64_MTE
+ orr x10, x10, mte_tcr
+ .unreq mte_tcr
+#endif
tcr_clear_errata_bits x10, x9, x5

#ifdef CONFIG_ARM64_VA_BITS_52
--
2.29.1.341.ge80a0c044ae-goog