[PATCH v2 24/37] arm64: mte: Add in-kernel tag fault handler

[Andrey Konovalov]

From: Vincenzo Frascino <vincenzo.frascino at arm.com>

Add the implementation of the in-kernel fault handler.

When a tag fault happens on a kernel address:
* a warning is logged,
* MTE is disabled on the current CPU,
* the execution continues.

When a tag fault happens on a user address:
* the kernel executes do_bad_area() and panics.

Signed-off-by: Vincenzo Frascino <vincenzo.frascino at arm.com>
Co-developed-by: Andrey Konovalov <andreyknvl at google.com>
Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
---
Change-Id: I9b8aa79567f7c45f4d6a1290efcf34567e620717
---
 arch/arm64/mm/fault.c | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index a3bd189602df..cdc23662691c 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -33,6 +33,7 @@
 #include <asm/debug-monitors.h>
 #include <asm/esr.h>
 #include <asm/kprobes.h>
+#include <asm/mte.h>
 #include <asm/processor.h>
 #include <asm/sysreg.h>
 #include <asm/system_misc.h>
@@ -294,6 +295,18 @@ static void die_kernel_fault(const char *msg, unsigned long addr,
 	do_exit(SIGKILL);
 }
 
+static void report_tag_fault(unsigned long addr, unsigned int esr,
+			     struct pt_regs *regs)
+{
+	bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
+
+	pr_alert("Memory Tagging Extension Fault in %pS\n", (void *)regs->pc);
+	pr_alert("  %s at address %lx\n", is_write ? "Write" : "Read", addr);
+	pr_alert("  Pointer tag: [%02x], memory tag: [%02x]\n",
+			mte_get_ptr_tag(addr),
+			mte_get_mem_tag((void *)addr));
+}
+
 static void __do_kernel_fault(unsigned long addr, unsigned int esr,
 			      struct pt_regs *regs)
 {
@@ -641,10 +654,31 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
 	return 0;
 }
 
+static void do_tag_recovery(unsigned long addr, unsigned int esr,
+			   struct pt_regs *regs)
+{
+	report_tag_fault(addr, esr, regs);
+
+	/*
+	 * Disable Memory Tagging Extension Tag Checking on the local CPU
+	 * for the current EL.
+	 * It will be done lazily on the other CPUs when they will hit a
+	 * tag fault.
+	 */
+	sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_NONE);
+	isb();
+}
+
+
 static int do_tag_check_fault(unsigned long addr, unsigned int esr,
 			      struct pt_regs *regs)
 {
-	do_bad_area(addr, esr, regs);
+	/* The tag check fault (TCF) is per TTBR */
+	if (is_ttbr0_addr(addr))
+		do_bad_area(addr, esr, regs);
+	else
+		do_tag_recovery(addr, esr, regs);
+
 	return 0;
 }
 
-- 
2.28.0.618.gf4bc123cb7-goog