The patch titled
Subject: arm64: mte: add in-kernel tag fault handler
has been added to the -mm tree. Its filename is
arm64-mte-add-in-kernel-tag-fault-handler.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/arm64-mte-add-in-kernel-tag-fault-handler.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/arm64-mte-add-in-kernel-tag-fault-handler.patch
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------------------------------------------------------
From: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
Subject: arm64: mte: add in-kernel tag fault handler
Add the implementation of the in-kernel fault handler.
When a tag fault happens on a kernel address:
* 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.
The tag fault handler for kernel addresses is currently empty and will be
filled in by a future commit.
Link: https://lkml.kernel.org/r/96694ab6b5b64f4ab2de32cdc4773857966d62f1.1605046192.git.andreyknvl@xxxxxxxxxx
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
Co-developed-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Branislav Rankov <Branislav.Rankov@xxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Evgenii Stepanov <eugenis@xxxxxxxxxx>
Cc: Kevin Brodsky <kevin.brodsky@xxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/uaccess.h | 23 ++++++++++++++
arch/arm64/mm/fault.c | 45 +++++++++++++++++++++++++++++
2 files changed, 68 insertions(+)
--- a/arch/arm64/include/asm/uaccess.h~arm64-mte-add-in-kernel-tag-fault-handler
+++ a/arch/arm64/include/asm/uaccess.h
@@ -200,13 +200,36 @@ do { \
CONFIG_ARM64_PAN)); \
} while (0)
+/*
+ * The Tag Check Flag (TCF) mode for MTE is per EL, hence TCF0
+ * affects EL0 and TCF affects EL1 irrespective of which TTBR is
+ * used.
+ * The kernel accesses TTBR0 usually with LDTR/STTR instructions
+ * when UAO is available, so these would act as EL0 accesses using
+ * TCF0.
+ * However futex.h code uses exclusives which would be executed as
+ * EL1, this can potentially cause a tag check fault even if the
+ * user disables TCF0.
+ *
+ * To address the problem we set the PSTATE.TCO bit in uaccess_enable()
+ * and reset it in uaccess_disable().
+ *
+ * The Tag check override (TCO) bit disables temporarily the tag checking
+ * preventing the issue.
+ */
static inline void uaccess_disable(void)
{
+ asm volatile(ALTERNATIVE("nop", SET_PSTATE_TCO(0),
+ ARM64_MTE, CONFIG_KASAN_HW_TAGS));
+
__uaccess_disable(ARM64_HAS_PAN);
}
static inline void uaccess_enable(void)
{
+ asm volatile(ALTERNATIVE("nop", SET_PSTATE_TCO(1),
+ ARM64_MTE, CONFIG_KASAN_HW_TAGS));
+
__uaccess_enable(ARM64_HAS_PAN);
}
--- a/arch/arm64/mm/fault.c~arm64-mte-add-in-kernel-tag-fault-handler
+++ a/arch/arm64/mm/fault.c
@@ -34,6 +34,7 @@
#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>
@@ -297,6 +298,44 @@ static void die_kernel_fault(const char
do_exit(SIGKILL);
}
+static void report_tag_fault(unsigned long addr, unsigned int esr,
+ struct pt_regs *regs)
+{
+}
+
+static void do_tag_recovery(unsigned long addr, unsigned int esr,
+ struct pt_regs *regs)
+{
+ static bool reported = false;
+
+ if (!READ_ONCE(reported)) {
+ report_tag_fault(addr, esr, regs);
+ WRITE_ONCE(reported, true);
+ }
+
+ /*
+ * Disable MTE 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 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 void __do_kernel_fault(unsigned long addr, unsigned int esr,
struct pt_regs *regs)
{
@@ -313,6 +352,12 @@ static void __do_kernel_fault(unsigned l
"Ignoring spurious kernel translation fault at virtual address %016lx\n", addr))
return;
+ if (is_el1_mte_sync_tag_check_fault(esr)) {
+ do_tag_recovery(addr, esr, regs);
+
+ return;
+ }
+
if (is_el1_permission_fault(addr, esr, regs)) {
if (esr & ESR_ELx_WNR)
msg = "write to read-only memory";
_
Patches currently in -mm which might be from vincenzo.frascino@xxxxxxx are
mm-vmalloc-fix-kasan-shadow-poisoning-size.patch
arm64-enable-armv85-a-asm-arch-option.patch
arm64-mte-add-in-kernel-mte-helpers.patch
arm64-mte-reset-the-page-tag-in-page-flags.patch
arm64-mte-add-in-kernel-tag-fault-handler.patch
arm64-kasan-allow-enabling-in-kernel-mte.patch
arm64-mte-convert-gcr_user-into-an-exclude-mask.patch
arm64-mte-switch-gcr_el1-in-kernel-entry-and-exit.patch
kasan-mm-untag-page-address-in-free_reserved_area.patch
kselftest-arm64-check-gcr_el1-after-context-switch.patch
