[PATCH v3] arm64: mte: move register initialization to C

[Evgenii Stepanov]

If FEAT_MTE2 is disabled via the arm64.nomte command line argument on a
CPU that claims to support FEAT_MTE2, the kernel will use Tagged Normal
in the MAIR. If we interpret arm64.nomte to mean that the CPU does not
in fact implement FEAT_MTE2, setting the system register like this may
lead to UNSPECIFIED behavior. Fix it by arranging for MAIR to be set
in the C function cpu_enable_mte which is called based on the sanitized
version of the system register.

There is no need for the rest of the MTE-related system register
initialization to happen from assembly, with the exception of TCR_EL1,
which must be set to include at least TBI1 because the secondary CPUs
access KASan-allocated data structures early. Therefore, make the TCR_EL1
initialization unconditional and move the rest of the initialization to
cpu_enable_mte so that we no longer have a dependency on the unsanitized
ID register value.

Signed-off-by: Peter Collingbourne <pcc@xxxxxxxxxx>
Signed-off-by: Evgenii Stepanov <eugenis@xxxxxxxxxx>
Suggested-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Link: https://lore.kernel.org/linux-arm-kernel/YwCsIm2nCXCEEgAd@xxxxxxx/T/
Link: https://linux-review.googlesource.com/id/I2c7df6bd4ea2dfc59376a8b9b5d3562b015c7198
---
Changelog since v2:
- Fixed register initialization on cpu_resume code path.

Changelog since v1:
- Keep TBI1 off unless CONFIG_ARM64_MTE
- Fixed mask application in the RGSR_EL1 computation (bug found by Kenny
  Root).
- Changed code formatting

 arch/arm64/include/asm/mte.h   |  2 ++
 arch/arm64/kernel/cpufeature.c |  2 ++
 arch/arm64/kernel/mte.c        | 51 ++++++++++++++++++++++++++++++++++
 arch/arm64/kernel/suspend.c    |  2 ++
 arch/arm64/mm/proc.S           | 46 ++++--------------------------
 5 files changed, 62 insertions(+), 41 deletions(-)

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index aa523591a44e5..5e80315e71894 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -42,7 +42,9 @@ void mte_sync_tags(pte_t old_pte, pte_t pte);
 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_cpu_setup(void);
 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,
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index af4de817d7123..fdc28f8e3307b 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2036,6 +2036,8 @@ static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap)
 	sysreg_clear_set(sctlr_el1, 0, SCTLR_ELx_ATA | SCTLR_EL1_ATA0);
 	isb();
 
+	mte_cpu_setup();
+
 	/*
 	 * Clear the tags in the zero page. This needs to be done via the
 	 * linear map which has the Tagged attribute.
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index b2b730233274b..aca88470fb69d 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -285,6 +285,49 @@ void mte_thread_switch(struct task_struct *next)
 	mte_check_tfsr_el1();
 }
 
+void mte_cpu_setup(void)
+{
+	u64 rgsr;
+
+	/*
+	 * CnP must be enabled only after the MAIR_EL1 register has been set
+	 * up. Inconsistent MAIR_EL1 between CPUs sharing the same TLB may
+	 * lead to the wrong memory type being used for a brief window during
+	 * CPU power-up.
+	 *
+	 * CnP is not a boot feature so MTE gets enabled before CnP, but let's
+	 * make sure that is the case.
+	 */
+	BUG_ON(read_sysreg(ttbr0_el1) & TTBR_CNP_BIT);
+	BUG_ON(read_sysreg(ttbr1_el1) & TTBR_CNP_BIT);
+
+	/* Normal Tagged memory type at the corresponding MAIR index */
+	sysreg_clear_set(mair_el1,
+			 MAIR_ATTRIDX(MAIR_ATTR_MASK, MT_NORMAL_TAGGED),
+			 MAIR_ATTRIDX(MAIR_ATTR_NORMAL_TAGGED,
+				      MT_NORMAL_TAGGED));
+
+	write_sysreg_s(KERNEL_GCR_EL1, SYS_GCR_EL1);
+
+	/*
+	 * If GCR_EL1.RRND=1 is implemented the same way as RRND=0, then
+	 * RGSR_EL1.SEED must be non-zero for IRG to produce
+	 * pseudorandom numbers. As RGSR_EL1 is UNKNOWN out of reset, we
+	 * must initialize it.
+	 */
+	rgsr = (read_sysreg(CNTVCT_EL0) & SYS_RGSR_EL1_SEED_MASK) <<
+	       SYS_RGSR_EL1_SEED_SHIFT;
+	if (rgsr == 0)
+		rgsr = 1 << SYS_RGSR_EL1_SEED_SHIFT;
+	write_sysreg_s(rgsr, SYS_RGSR_EL1);
+
+	/* clear any pending tag check faults in TFSR*_EL1 */
+	write_sysreg_s(0, SYS_TFSR_EL1);
+	write_sysreg_s(0, SYS_TFSRE0_EL1);
+
+	local_flush_tlb_all();
+}
+
 void mte_suspend_enter(void)
 {
 	if (!system_supports_mte())
@@ -301,6 +344,14 @@ void mte_suspend_enter(void)
 	mte_check_tfsr_el1();
 }
 
+void mte_suspend_exit(void)
+{
+	if (!system_supports_mte())
+		return;
+
+	mte_cpu_setup();
+}
+
 long set_mte_ctrl(struct task_struct *task, unsigned long arg)
 {
 	u64 mte_ctrl = (~((arg & PR_MTE_TAG_MASK) >> PR_MTE_TAG_SHIFT) &
diff --git a/arch/arm64/kernel/suspend.c b/arch/arm64/kernel/suspend.c
index 9135fe0f3df53..8b02d310838f9 100644
--- a/arch/arm64/kernel/suspend.c
+++ b/arch/arm64/kernel/suspend.c
@@ -43,6 +43,8 @@ void notrace __cpu_suspend_exit(void)
 {
 	unsigned int cpu = smp_processor_id();
 
+	mte_suspend_exit();
+
 	/*
 	 * We are resuming from reset with the idmap active in TTBR0_EL1.
 	 * We must uninstall the idmap and restore the expected MMU
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 7837a69524c53..f38bccdd374a5 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -48,17 +48,19 @@
 
 #ifdef CONFIG_KASAN_HW_TAGS
 #define TCR_MTE_FLAGS TCR_TCMA1 | TCR_TBI1 | TCR_TBID1
-#else
+#elif defined(CONFIG_ARM64_MTE)
 /*
  * The mte_zero_clear_page_tags() implementation uses DC GZVA, which relies on
  * TBI being enabled at EL1.
  */
 #define TCR_MTE_FLAGS TCR_TBI1 | TCR_TBID1
+#else
+#define TCR_MTE_FLAGS 0
 #endif
 
 /*
  * Default MAIR_EL1. MT_NORMAL_TAGGED is initially mapped as Normal memory and
- * changed during __cpu_setup to Normal Tagged if the system supports MTE.
+ * changed during mte_cpu_setup to Normal Tagged if the system supports MTE.
  */
 #define MAIR_EL1_SET							\
 	(MAIR_ATTRIDX(MAIR_ATTR_DEVICE_nGnRnE, MT_DEVICE_nGnRnE) |	\
@@ -426,46 +428,8 @@ SYM_FUNC_START(__cpu_setup)
 	mov_q	mair, MAIR_EL1_SET
 	mov_q	tcr, TCR_TxSZ(VA_BITS) | TCR_CACHE_FLAGS | TCR_SMP_FLAGS | \
 			TCR_TG_FLAGS | TCR_KASLR_FLAGS | TCR_ASID16 | \
-			TCR_TBI0 | TCR_A1 | TCR_KASAN_SW_FLAGS
-
-#ifdef CONFIG_ARM64_MTE
-	/*
-	 * Update MAIR_EL1, GCR_EL1 and TFSR*_EL1 if MTE is supported
-	 * (ID_AA64PFR1_EL1[11:8] > 1).
-	 */
-	mrs	x10, ID_AA64PFR1_EL1
-	ubfx	x10, x10, #ID_AA64PFR1_MTE_SHIFT, #4
-	cmp	x10, #ID_AA64PFR1_MTE
-	b.lt	1f
-
-	/* Normal Tagged memory type at the corresponding MAIR index */
-	mov	x10, #MAIR_ATTR_NORMAL_TAGGED
-	bfi	mair, x10, #(8 *  MT_NORMAL_TAGGED), #8
+			TCR_TBI0 | TCR_A1 | TCR_KASAN_SW_FLAGS | TCR_MTE_FLAGS
 
-	mov	x10, #KERNEL_GCR_EL1
-	msr_s	SYS_GCR_EL1, x10
-
-	/*
-	 * If GCR_EL1.RRND=1 is implemented the same way as RRND=0, then
-	 * RGSR_EL1.SEED must be non-zero for IRG to produce
-	 * pseudorandom numbers. As RGSR_EL1 is UNKNOWN out of reset, we
-	 * must initialize it.
-	 */
-	mrs	x10, CNTVCT_EL0
-	ands	x10, x10, #SYS_RGSR_EL1_SEED_MASK
-	csinc	x10, x10, xzr, ne
-	lsl	x10, x10, #SYS_RGSR_EL1_SEED_SHIFT
-	msr_s	SYS_RGSR_EL1, x10
-
-	/* 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	x10, TCR_MTE_FLAGS
-	orr	tcr, tcr, x10
-1:
-#endif
 	tcr_clear_errata_bits tcr, x9, x5
 
 #ifdef CONFIG_ARM64_VA_BITS_52
-- 
2.37.2.789.g6183377224-goog