diff options
Diffstat (limited to 'share/man/man4/hwpmc.4')
| -rw-r--r-- | share/man/man4/hwpmc.4 | 72 |
1 files changed, 36 insertions, 36 deletions
diff --git a/share/man/man4/hwpmc.4 b/share/man/man4/hwpmc.4 index 7034cd4..6264bd0 100644 --- a/share/man/man4/hwpmc.4 +++ b/share/man/man4/hwpmc.4 @@ -450,42 +450,6 @@ These variables may be set in the kernel environment using before .Nm is loaded. -.Sh SECURITY CONSIDERATIONS -PMCs may be used to monitor the actual behavior of the system on hardware. -In situations where this constitutes an undesirable information leak, -the following options are available: -.Bl -enum -.It -Set the -.Xr sysctl 8 -tunable -.Va security.bsd.unprivileged_syspmcs -to 0. -This ensures that unprivileged processes cannot allocate system-wide -PMCs and thus cannot observe the hardware behavior of the system -as a whole. -This tunable may also be set at boot time using -.Xr loader 8 , -or with -.Xr kenv 1 -prior to loading the -.Nm -driver into the kernel. -.It -Set the -.Xr sysctl 8 -tunable -.Va security.bsd.unprivileged_proc_debug -to 0. -This will ensure that an unprivileged process cannot attach a PMC -to any process other than itself and thus cannot observe the hardware -behavior of other processes with the same credentials. -.El -.Pp -System administrators should note that on IA-32 platforms -.Fx -makes the content of the IA-32 TSC counter available to all processes -via the RDTSC instruction. .Sh IMPLEMENTATION NOTES .Ss SMP Symmetry The kernel driver requires all physical CPUs in an SMP system to have @@ -831,3 +795,39 @@ Many single-processor motherboards keep the APIC disabled in BIOS; on such systems .Nm will not support sampling PMCs. +.Sh SECURITY CONSIDERATIONS +PMCs may be used to monitor the actual behavior of the system on hardware. +In situations where this constitutes an undesirable information leak, +the following options are available: +.Bl -enum +.It +Set the +.Xr sysctl 8 +tunable +.Va security.bsd.unprivileged_syspmcs +to 0. +This ensures that unprivileged processes cannot allocate system-wide +PMCs and thus cannot observe the hardware behavior of the system +as a whole. +This tunable may also be set at boot time using +.Xr loader 8 , +or with +.Xr kenv 1 +prior to loading the +.Nm +driver into the kernel. +.It +Set the +.Xr sysctl 8 +tunable +.Va security.bsd.unprivileged_proc_debug +to 0. +This will ensure that an unprivileged process cannot attach a PMC +to any process other than itself and thus cannot observe the hardware +behavior of other processes with the same credentials. +.El +.Pp +System administrators should note that on IA-32 platforms +.Fx +makes the content of the IA-32 TSC counter available to all processes +via the RDTSC instruction. |
