Drivers: hv: vmbus: Deactivate sysctl_record_panic_msg by default in isolated guests

[ Upstream commit 9f8b577f7b43b2170628d6c537252785dcc2dcea ]

hv_panic_page might contain guest-sensitive information, do not dump it
over to Hyper-V by default in isolated guests.

While at it, update some comments in hyperv_{panic,die}_event().

Reported-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Link: https://lore.kernel.org/r/20220301141135.2232-1-parri.andrea@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index a939ca1..aea8125 100644 (file)
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -76,8 +76,8 @@ static int hyperv_panic_event(struct notifier_block *nb, unsigned long val,
 
        /*
         * Hyper-V should be notified only once about a panic.  If we will be
-        * doing hyperv_report_panic_msg() later with kmsg data, don't do
-        * the notification here.
+        * doing hv_kmsg_dump() with kmsg data later, don't do the notification
+        * here.
         */
        if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE
            && hyperv_report_reg()) {
@@ -99,8 +99,8 @@ static int hyperv_die_event(struct notifier_block *nb, unsigned long val,
 
        /*
         * Hyper-V should be notified only once about a panic.  If we will be
-        * doing hyperv_report_panic_msg() later with kmsg data, don't do
-        * the notification here.
+        * doing hv_kmsg_dump() with kmsg data later, don't do the notification
+        * here.
         */
        if (hyperv_report_reg())
                hyperv_report_panic(regs, val, true);
@@ -1545,14 +1545,20 @@ static int vmbus_bus_init(void)
        if (ret)
                goto err_connect;
 
+       if (hv_is_isolation_supported())
+               sysctl_record_panic_msg = 0;
+
        /*
         * Only register if the crash MSRs are available
         */
        if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE) {
                u64 hyperv_crash_ctl;
                /*
-                * Sysctl registration is not fatal, since by default
-                * reporting is enabled.
+                * Panic message recording (sysctl_record_panic_msg)
+                * is enabled by default in non-isolated guests and
+                * disabled by default in isolated guests; the panic
+                * message recording won't be available in isolated
+                * guests should the following registration fail.
                 */
                hv_ctl_table_hdr = register_sysctl_table(hv_root_table);
                if (!hv_ctl_table_hdr)