Coresight ETF NULL pointer dereference and ETM save/restore fixes

This 2 patch series provides fixes to ETF null pointer dereference crash and TRCVMIDCCTLR1 register save and restore fix.

Patch 1 is an RFC since I am not sure of the fix provided since it looks more like a band-aid than the actual fix.

Sai Prakash Ranjan (2):
coresight: tmc-etf: Fix NULL pointer dereference in
tmc_enable_etf_sink_perf()
coresight: etm4x: Fix save and restore of TRCVMIDCCTLR1 register

 drivers/hwtracing/coresight/coresight-etm4x-core.c | 4 ++--
 drivers/hwtracing/coresight/coresight-tmc-etf.c    | 3 +++
 2 files changed, 5 insertions(+), 2 deletions(-)

base-commit: e209e73bee253afe969410150248f0c300c13d84

QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation

There was a report of NULL pointer dereference in ETF enable path for perf CS mode with PID. It is almost 100% reproducible when the process to monitor is something very active such as chrome and only with ETF as the sink. Currently in a bid to find the pid, the owner is dereferenced via task_pid_nr() call in tmc_enable_etf_sink_perf(). With owner being NULL, we get a NULL pointer dereference, so check the owner before dereferencing it to prevent the system crash.

perf record -e cs_etm/@tmc_etf0/ -N -p <pid>

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000548

Mem abort info:
ESR = 0x96000006
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
Data abort info:
ISV = 0, ISS = 0x00000006
CM = 0, WnR = 0

Call trace:
 tmc_enable_etf_sink+0xe4/0x280
 coresight_enable_path+0x168/0x1fc
 etm_event_start+0x8c/0xf8
 etm_event_add+0x38/0x54
 event_sched_in+0x194/0x2ac
 group_sched_in+0x54/0x12c
 flexible_sched_in+0xd8/0x120
 visit_groups_merge+0x100/0x16c
 ctx_flexible_sched_in+0x50/0x74
 ctx_sched_in+0xa4/0xa8
 perf_event_sched_in+0x60/0x6c
 perf_event_context_sched_in+0x98/0xe0
 __perf_event_task_sched_in+0x5c/0xd8
 finish_task_switch+0x184/0x1cc
 schedule_tail+0x20/0xec
 ret_from_fork+0x4/0x18

---

I am not sure of this incomplete solution hence the RFC. This issue was also reported when this code was first added [1] but somehow it didn't get much notice at the time. So the NULL pointer is propagated from as far as flexible_sched_in() (might even be earlier than this) in events core and deferenced in ETF code where it crashes. So I am not sure if its a problem with the core code or the etf driver. Plus it is not reproducible with all the processes, just something which is quite active ones such as chrome. This is with 5.4 kernel with all the coresight patches backported, I did go through events/core code from latest kernel to see if we are missing any fixes related to this but I couldn't find any so I believe this problem should also exist on latest kernel as well.

[1] https://lists.linaro.org/pipermail/coresight/2019-March/002278.html

---
 drivers/hwtracing/coresight/coresight-tmc-etf.c | 3 +++
 1 file changed, 3 insertions(+)

index 44402d413ebb..32f141d943ca 100644
@@ -242,6 +242,9 @@ static int tmc_enable_etf_sink_perf(struct coresight_device *csdev, void *data)
 			break;
 		}
 
+		if (!handle->event->owner)
+			break;
+
 		/* Get a handle on the pid of the process to monitor */
 		pid = task_pid_nr(handle->event->owner);
 

QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation

In commit f188b5e76aae ("coresight: etm4x: Save/restore state across CPU low power states"), mistakenly TRCVMIDCCTLR1 register value was saved in trcvmidcctlr0 state variable which is used to store TRCVMIDCCTLR0 register value in etm4x_cpu_save() and then same value is written back to both TRCVMIDCCTLR0 and TRCVMIDCCTLR1 in etm4x_cpu_restore(). There is already a trcvmidcctlr1 state variable available for TRCVMIDCCTLR1, so use it.

---
 drivers/hwtracing/coresight/coresight-etm4x-core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index de76d57850bc..abd706b216ac 100644
@@ -1243,7 +1243,7 @@ static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
 	state->trccidcctlr1 = readl(drvdata->base + TRCCIDCCTLR1);
 
 	state->trcvmidcctlr0 = readl(drvdata->base + TRCVMIDCCTLR0);
-	state->trcvmidcctlr0 = readl(drvdata->base + TRCVMIDCCTLR1);
+	state->trcvmidcctlr1 = readl(drvdata->base + TRCVMIDCCTLR1);
 
 	state->trcclaimset = readl(drvdata->base + TRCCLAIMCLR);
 

@@ -1353,7 +1353,7 @@ static void etm4_cpu_restore(struct etmv4_drvdata *drvdata)
 	writel_relaxed(state->trccidcctlr1, drvdata->base + TRCCIDCCTLR1);
 
 	writel_relaxed(state->trcvmidcctlr0, drvdata->base + TRCVMIDCCTLR0);
-	writel_relaxed(state->trcvmidcctlr0, drvdata->base + TRCVMIDCCTLR1);
+	writel_relaxed(state->trcvmidcctlr1, drvdata->base + TRCVMIDCCTLR1);
 
 	writel_relaxed(state->trcclaimset, drvdata->base + TRCCLAIMSET);
 

QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation

Hi Sai,

Why is this commit in question ?

I believe this is the right fixes tag.

Hi Suzuki,

My bad sorry, I thought there are two commits which touch this hunk of code, but I see now that the module code just renamed the file, so this fixes tag is not required.

Yes, I will resend with only this fixes tag.

Thanks,
Sai

QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
of Code Aurora Forum, hosted by The Linux Foundation