Author: markj
Date: Thu Feb 16 23:05:20 2017
New Revision: 313841
URL: https://svnweb.freebsd.org/changeset/base/313841
Log:
Prevent CPU migration when checking the DTrace nofault flag on x86.
dtrace_trap() consumes page and protection faults triggered by code running
in DTrace probe context. Such faults occur with interrupts disabled and are
detected using a per-CPU flag. Regular faults cause dtrace_trap() to be
called with interrupts enabled, and nothing was ensuring that the flag was
read from the correct CPU. This may result in dtrace_trap() consuming
unrelated page and protection faults when DTrace is enabled, causing the
fault handler to return without actually having handled the fault.
Diagnosed by: Ryan Libby <rli...@gmail.com>
MFC after: 3 days
Sponsored by: Dell EMC Isilon
Modified:
head/sys/cddl/dev/dtrace/amd64/dtrace_subr.c
head/sys/cddl/dev/dtrace/i386/dtrace_subr.c
Modified: head/sys/cddl/dev/dtrace/amd64/dtrace_subr.c
==============================================================================
--- head/sys/cddl/dev/dtrace/amd64/dtrace_subr.c Thu Feb 16 22:29:37
2017 (r313840)
+++ head/sys/cddl/dev/dtrace/amd64/dtrace_subr.c Thu Feb 16 23:05:20
2017 (r313841)
@@ -384,6 +384,8 @@ dtrace_gethrestime(void)
int
dtrace_trap(struct trapframe *frame, u_int type)
{
+ uint16_t nofault;
+
/*
* A trap can occur while DTrace executes a probe. Before
* executing the probe, DTrace blocks re-scheduling and sets
@@ -393,7 +395,12 @@ dtrace_trap(struct trapframe *frame, u_i
*
* Check if DTrace has enabled 'no-fault' mode:
*/
- if ((cpu_core[curcpu].cpuc_dtrace_flags & CPU_DTRACE_NOFAULT) != 0) {
+ sched_pin();
+ nofault = cpu_core[curcpu].cpuc_dtrace_flags & CPU_DTRACE_NOFAULT;
+ sched_unpin();
+ if (nofault) {
+ KASSERT((read_rflags() & PSL_I) == 0, ("interrupts enabled"));
+
/*
* There are only a couple of trap types that are expected.
* All the rest will be handled in the usual way.
Modified: head/sys/cddl/dev/dtrace/i386/dtrace_subr.c
==============================================================================
--- head/sys/cddl/dev/dtrace/i386/dtrace_subr.c Thu Feb 16 22:29:37 2017
(r313840)
+++ head/sys/cddl/dev/dtrace/i386/dtrace_subr.c Thu Feb 16 23:05:20 2017
(r313841)
@@ -386,6 +386,8 @@ dtrace_gethrestime(void)
int
dtrace_trap(struct trapframe *frame, u_int type)
{
+ uint16_t nofault;
+
/*
* A trap can occur while DTrace executes a probe. Before
* executing the probe, DTrace blocks re-scheduling and sets
@@ -395,7 +397,12 @@ dtrace_trap(struct trapframe *frame, u_i
*
* Check if DTrace has enabled 'no-fault' mode:
*/
- if ((cpu_core[curcpu].cpuc_dtrace_flags & CPU_DTRACE_NOFAULT) != 0) {
+ sched_pin();
+ nofault = cpu_core[curcpu].cpuc_dtrace_flags & CPU_DTRACE_NOFAULT;
+ sched_unpin();
+ if (nofault) {
+ KASSERT((read_eflags() & PSL_I) == 0, ("interrupts enabled"));
+
/*
* There are only a couple of trap types that are expected.
* All the rest will be handled in the usual way.
_______________________________________________
svn-src-head@freebsd.org mailing list
https://lists.freebsd.org/mailman/listinfo/svn-src-head
To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
