[PATCH 21/35] 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,
* the faulting instruction is skipped,
* 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>
---
 arch/arm64/mm/fault.c | 50 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 49 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 5e832b3387f1..c62c8ba85c0e 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>
@@ -222,6 +223,20 @@ int ptep_set_access_flags(struct vm_area_struct *vma,
 	return 1;
 }
 
+static bool is_el1_mte_sync_tag_check_fault(unsigned int esr)
+{
+	unsigned int ec = ESR_ELx_EC(esr);
+	unsigned int fsc = esr & ESR_ELx_FSC;
+
+	if (ec != ESR_ELx_EC_DABT_CUR)
+		return false;
+
+	if (fsc == ESR_ELx_FSC_MTE)
+		return true;
+
+	return false;
+}
+
 static bool is_el1_instruction_abort(unsigned int esr)
 {
 	return ESR_ELx_EC(esr) == ESR_ELx_EC_IABT_CUR;
@@ -294,6 +309,18 @@ 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)
 {
@@ -317,12 +344,16 @@ static void __do_kernel_fault(unsigned long addr, unsigned int esr,
 			msg = "execute from non-executable memory";
 		else
 			msg = "read from unreadable memory";
+	} else if (is_el1_mte_sync_tag_check_fault(esr)) {
+		report_tag_fault(addr, esr, regs);
+		msg = "memory tagging extension fault";
 	} else if (addr < PAGE_SIZE) {
 		msg = "NULL pointer dereference";
 	} else {
 		msg = "paging request";
 	}
 
+
 	die_kernel_fault(msg, addr, esr, regs);
 }
 
@@ -658,10 +689,27 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
 	return 0;
 }
 
+static int do_tag_recovery(unsigned long addr, unsigned int esr,
+			   struct pt_regs *regs)
+{
+	report_tag_fault(addr, esr, regs);
+
+	/* Skip over the faulting instruction and continue: */
+	arm64_skip_faulting_instruction(regs, AARCH64_INSN_SIZE);
+
+	return 0;
+}
+
+
 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;
 }
 
-- 
2.28.0.220.ged08abb693-goog