linux-kernel - [PATCH v2 25/37] arm64: kasan: Enable in-kernel MTE

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Date:   Tue, 15 Sep 2020 23:16:07 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        kasan-dev@...glegroups.com
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Elena Petrova <lenaptr@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH v2 25/37] arm64: kasan: Enable in-kernel MTE

From: Vincenzo Frascino <vincenzo.frascino@....com>

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

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

Enable MTE in Synchronous mode in EL1 to provide a more immediate
way of tag check failure detection in the kernel.

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.

Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
---
Change-Id: I4d67497268bb7f0c2fc5dcacefa1e273df4af71d
---
 arch/arm64/kernel/cpufeature.c |  7 +++++++
 arch/arm64/mm/proc.S           | 13 +++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index add9da5d8ea3..eca06b8c74db 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1718,6 +1718,13 @@ static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap)
 		cleared_zero_page = true;
 		mte_clear_page_tags(lm_alias(empty_zero_page));
 	}
+
+	/* Enable in-kernel MTE only if KASAN_HW_TAGS is enabled */
+	if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) {
+		/* Enable MTE Sync Mode for EL1 */
+		sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
+		isb();
+	}
 }
 #endif /* CONFIG_ARM64_MTE */
 
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 23c326a06b2d..5ba7ac5e9c77 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -427,6 +427,10 @@ SYM_FUNC_START(__cpu_setup)
 	 */
 	mov_q	x5, MAIR_EL1_SET
 #ifdef CONFIG_ARM64_MTE
+	mte_present	.req	x20
+
+	mov	mte_present, #0
+
 	/*
 	 * Update MAIR_EL1, GCR_EL1 and TFSR*_EL1 if MTE is supported
 	 * (ID_AA64PFR1_EL1[11:8] > 1).
@@ -447,6 +451,8 @@ 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
+
+	mov	mte_present, #1
 1:
 #endif
 	msr	mair_el1, x5
@@ -485,6 +491,13 @@ SYM_FUNC_START(__cpu_setup)
 	orr	x10, x10, #TCR_HA		// hardware Access flag update
 1:
 #endif	/* CONFIG_ARM64_HW_AFDBM */
+#ifdef CONFIG_ARM64_MTE
+	/* Update TCR_EL1 if MTE is supported (ID_AA64PFR1_EL1[11:8] > 1) */
+	cbz	mte_present, 1f
+	orr	x10, x10, #SYS_TCR_EL1_TCMA1
+1:
+	.unreq	mte_present
+#endif
 	msr	tcr_el1, x10
 	/*
 	 * Prepare SCTLR
-- 
2.28.0.618.gf4bc123cb7-goog