coresight: etm4x: Use Trace Filtering controls dynamically

The Trace Filtering support (FEAT_TRF) ensures that the ETM
can be prohibited from generating any trace for a given EL.
This is much stricter knob, than the TRCVICTLR exception level
masks, which doesn't prevent the ETM from generating Context
packets for an "excluded" EL. At the moment, we do a onetime
enable trace at user and kernel and leave it untouched for the
kernel life time. This implies that the ETM could potentially
generate trace packets containing the kernel addresses, and
thus leaking the kernel virtual address in the trace.

This patch makes the switch dynamic, by honoring the filters
set by the user and enforcing them in the TRFCR controls.
We also rename the cpu_enable_tracing() appropriately to
cpu_detect_trace_filtering() and the drvdata member
trfc => trfcr to indicate the "value" of the TRFCR_EL1.

Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Al Grant <al.grant@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20210914102641.1852544-3-suzuki.poulose@arm.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

1 files changed, 47 insertions, 16 deletions

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 537c0d7ee1ed..d9a85ca25b60 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -239,6 +239,45 @@ struct etm4_enable_arg {
 	int rc;
 };
 
+/*
+ * etm4x_prohibit_trace - Prohibit the CPU from tracing at all ELs.
+ * When the CPU supports FEAT_TRF, we could move the ETM to a trace
+ * prohibited state by filtering the Exception levels via TRFCR_EL1.
+ */
+static void etm4x_prohibit_trace(struct etmv4_drvdata *drvdata)
+{
+	/* If the CPU doesn't support FEAT_TRF, nothing to do */
+	if (!drvdata->trfcr)
+		return;
+	cpu_prohibit_trace();
+}
+
+/*
+ * etm4x_allow_trace - Allow CPU tracing in the respective ELs,
+ * as configured by the drvdata->config.mode for the current
+ * session. Even though we have TRCVICTLR bits to filter the
+ * trace in the ELs, it doesn't prevent the ETM from generating
+ * a packet (e.g, TraceInfo) that might contain the addresses from
+ * the excluded levels. Thus we use the additional controls provided
+ * via the Trace Filtering controls (FEAT_TRF) to make sure no trace
+ * is generated for the excluded ELs.
+ */
+static void etm4x_allow_trace(struct etmv4_drvdata *drvdata)
+{
+	u64 trfcr = drvdata->trfcr;
+
+	/* If the CPU doesn't support FEAT_TRF, nothing to do */
+	if (!trfcr)
+		return;
+
+	if (drvdata->config.mode & ETM_MODE_EXCL_KERN)
+		trfcr &= ~TRFCR_ELx_ExTRE;
+	if (drvdata->config.mode & ETM_MODE_EXCL_USER)
+		trfcr &= ~TRFCR_ELx_E0TRE;
+
+	write_trfcr(trfcr);
+}
+
 #ifdef CONFIG_ETM4X_IMPDEF_FEATURE
 
 #define HISI_HIP08_AMBA_ID		0x000b6d01
@@ -443,6 +482,7 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
 	if (etm4x_is_ete(drvdata))
 		etm4x_relaxed_write32(csa, TRCRSR_TA, TRCRSR);
 
+	etm4x_allow_trace(drvdata);
 	/* Enable the trace unit */
 	etm4x_relaxed_write32(csa, 1, TRCPRGCTLR);
 
@@ -738,7 +778,6 @@ static int etm4_enable(struct coresight_device *csdev,
 static void etm4_disable_hw(void *info)
 {
 	u32 control;
-	u64 trfcr;
 	struct etmv4_drvdata *drvdata = info;
 	struct etmv4_config *config = &drvdata->config;
 	struct coresight_device *csdev = drvdata->csdev;
@@ -765,12 +804,7 @@ static void etm4_disable_hw(void *info)
 	 * If the CPU supports v8.4 Trace filter Control,
 	 * set the ETM to trace prohibited region.
 	 */
-	if (drvdata->trfc) {
-		trfcr = read_sysreg_s(SYS_TRFCR_EL1);
-		write_sysreg_s(trfcr & ~(TRFCR_ELx_ExTRE | TRFCR_ELx_E0TRE),
-			       SYS_TRFCR_EL1);
-		isb();
-	}
+	etm4x_prohibit_trace(drvdata);
 	/*
 	 * Make sure everything completes before disabling, as recommended
 	 * by section 7.3.77 ("TRCVICTLR, ViewInst Main Control Register,
@@ -786,9 +820,6 @@ static void etm4_disable_hw(void *info)
 	if (coresight_timeout(csa, TRCSTATR, TRCSTATR_PMSTABLE_BIT, 1))
 		dev_err(etm_dev,
 			"timeout while waiting for PM stable Trace Status\n");
-	if (drvdata->trfc)
-		write_sysreg_s(trfcr, SYS_TRFCR_EL1);
-
 	/* read the status of the single shot comparators */
 	for (i = 0; i < drvdata->nr_ss_cmp; i++) {
 		config->ss_status[i] =
@@ -990,15 +1021,15 @@ static bool etm4_init_csdev_access(struct etmv4_drvdata *drvdata,
 	return false;
 }
 
-static void cpu_enable_tracing(struct etmv4_drvdata *drvdata)
+static void cpu_detect_trace_filtering(struct etmv4_drvdata *drvdata)
 {
 	u64 dfr0 = read_sysreg(id_aa64dfr0_el1);
 	u64 trfcr;
 
+	drvdata->trfcr = 0;
 	if (!cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_TRACE_FILT_SHIFT))
 		return;
 
-	drvdata->trfc = true;
 	/*
 	 * If the CPU supports v8.4 SelfHosted Tracing, enable
 	 * tracing at the kernel EL and EL0, forcing to use the
@@ -1012,7 +1043,7 @@ static void cpu_enable_tracing(struct etmv4_drvdata *drvdata)
 	if (is_kernel_in_hyp_mode())
 		trfcr |= TRFCR_EL2_CX;
 
-	write_trfcr(trfcr);
+	drvdata->trfcr = trfcr;
 }
 
 static void etm4_init_arch_data(void *info)
@@ -1203,7 +1234,7 @@ static void etm4_init_arch_data(void *info)
 	/* NUMCNTR, bits[30:28] number of counters available for tracing */
 	drvdata->nr_cntr = BMVAL(etmidr5, 28, 30);
 	etm4_cs_lock(drvdata, csa);
-	cpu_enable_tracing(drvdata);
+	cpu_detect_trace_filtering(drvdata);
 }
 
 static inline u32 etm4_get_victlr_access_type(struct etmv4_config *config)
@@ -1699,7 +1730,7 @@ static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
 	int ret = 0;
 
 	/* Save the TRFCR irrespective of whether the ETM is ON */
-	if (drvdata->trfc)
+	if (drvdata->trfcr)
 		drvdata->save_trfcr = read_trfcr();
 	/*
 	 * Save and restore the ETM Trace registers only if
@@ -1808,7 +1839,7 @@ static void __etm4_cpu_restore(struct etmv4_drvdata *drvdata)
 
 static void etm4_cpu_restore(struct etmv4_drvdata *drvdata)
 {
-	if (drvdata->trfc)
+	if (drvdata->trfcr)
 		write_trfcr(drvdata->save_trfcr);
 	if (drvdata->state_needs_restore)
 		__etm4_cpu_restore(drvdata);