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Prevent CPU migration when checking the DTrace nofault flag on x86.

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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 <rlibby@gmail.com>
MFC after:	3 days
Sponsored by:	Dell EMC Isilon
This commit is contained in:
markj 2017-02-16 23:05:20 +00:00
parent 5e6a848492
commit 2a3b2874a6
2 changed files with 16 additions and 2 deletions
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9
sys/cddl/dev/dtrace/amd64/dtrace_subr.c
View File

@ -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_int type)
*
* 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.

9
sys/cddl/dev/dtrace/i386/dtrace_subr.c
View File

@ -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_int type)
*
* 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.