[PATCH v4] arm64: mte: move register initialization to C

Evgenii Stepanov
2022-09-07T00:36:40Z

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@google.com>
Signed-off-by: Evgenii Stepanov <eugenis@google.com>
Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: kernel test robot <lkp@intel.com>
---
Changelong since v3:
- Removed extra isb barrier.
- Fixed build without CONFIG_ARM64_MTE.

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 | 5 ++++
arch/arm64/kernel/cpufeature.c | 3 +-
arch/arm64/kernel/mte.c | 51 ++++++++++++++++++++++++++++++++++
arch/arm64/kernel/suspend.c | 2 ++
arch/arm64/mm/proc.S | 46 ++++--------------------------
5 files changed, 65 insertions(+), 42 deletions(-)

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index aa523591a44e5..760c62f8e22f8 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,
@@ -72,6 +74,9 @@ static inline void mte_thread_switch(struct task_struct *next)
static inline void mte_suspend_enter(void)
{
}
+static inline void mte_suspend_exit(void)
+{
+}
static inline long set_mte_ctrl(struct task_struct *task, unsigned long arg)
{
return 0;
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index af4de817d7123..d7a077b5ccd1c 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2034,7 +2034,8 @@ static void bti_enable(const struct arm64_cpu_capabilities *__unused)
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
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