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Stack walk loop breaker for ASGCT
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Prevent potential endless loop in the stack walker when examining the
stack of a thread which has been interrupted when not at a safe point.

Signed-off-by: Graham Chapman <graham_chapman@ca.ibm.com>
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@gacholio
gacholio committed Nov 9, 2022
1 parent fafe184 commit c4b3775
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Showing 3 changed files with 64 additions and 34 deletions.
14 changes: 6 additions & 8 deletions runtime/oti/j9consts.h
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Original file line number Diff line number Diff line change
Expand Up @@ -375,16 +375,14 @@ extern "C" {
#define J9_STARTPC_DLT_READY 0x8
#define J9_STARTPC_STATUS 0xF

/* Frame iterator return values */
#define J9_STACKWALK_STOP_ITERATING 0x0
#define J9_STACKWALK_KEEP_ITERATING 0x1

/* Stackwalk return values */
#define J9_STACKWALK_RC_NONE 0x0
#define J9_STACKWALK_RC_NO_MEMORY 0x1
#define J9_STACKWALK_RC_FRAME_NOT_FOUND 0x2
#define J9_STACKWALK_RC_BAD_STATE_BUFFER 0x3
#define J9_STACKWALK_RC_STACK_CORRUPT 0x4
#define J9_STACKWALK_STOP_ITERATING 0x0 /* Must be the same as no error */
#define J9_STACKWALK_KEEP_ITERATING 0x1
#define J9_STACKWALK_RC_NO_MEMORY 0x2
#define J9_STACKWALK_RC_FRAME_NOT_FOUND 0x3
#define J9_STACKWALK_RC_BAD_STATE_BUFFER 0x4
#define J9_STACKWALK_RC_STACK_CORRUPT 0x5

/* Tag for JIT artifact search cache */
#define J9_STACKWALK_NO_JIT_CACHE 0x1
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1 change: 1 addition & 0 deletions runtime/oti/j9nonbuilder.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2537,6 +2537,7 @@ typedef struct J9StackWalkState {
void* inlinedCallSite;
void* stackMap;
void* inlineMap;
UDATA loopBreaker;
/* The size of J9StackWalkState must be a multiple of 8 because it is inlined into
* J9VMThread where alignment assumotions are being made.
*/
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83 changes: 57 additions & 26 deletions runtime/vm/swalk.c
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Original file line number Diff line number Diff line change
Expand Up @@ -91,9 +91,40 @@ static void dropToCurrentFrame (J9StackWalkState * walkState);
/* The minimum number of stack slots that a stack frame can occupy */
#define J9_STACKWALK_MIN_FRAME_SLOTS (OMR_MIN(sizeof(J9JITFrame), sizeof(J9SFStackFrame)) / sizeof(UDATA))

static VMINLINE UDATA
maxFramesOnStack(J9StackWalkState *walkState)
{
J9VMThread *walkThread = walkState->walkThread;
J9JITConfig *jitConfig = walkThread->javaVM->jitConfig;
UDATA * endOfStack = walkThread->stackObject->end;
UDATA * sp = walkState->walkThread->sp;
UDATA maxFrames = (endOfStack - sp) / J9_STACKWALK_MIN_FRAME_SLOTS;

if (NULL != jitConfig) {
if (J9_ARE_NO_BITS_SET(walkState->flags, J9_STACKWALK_SKIP_INLINES)) {
/* It's possible every frame on the stack is a fully inlined JIT frame */
maxFrames *= (jitConfig->maxInlineDepth + 1);
}
}

if (J9_ARE_NO_BITS_SET(walkState->flags, J9_STACKWALK_NO_ERROR_REPORT)) {
UDATA * stackStart = J9_LOWEST_STACK_SLOT(walkState->walkThread);
#if defined(J9VM_INTERP_STACKWALK_TRACING)
Assert_VRB_true(sp >= stackStart);
Assert_VRB_true(sp <= endOfStack);
#else /* J9VM_INTERP_STACKWALK_TRACING */
Assert_VM_true(sp >= stackStart);
Assert_VM_true(sp <= endOfStack);
#endif /* J9VM_INTERP_STACKWALK_TRACING */
}

return maxFrames;
}

UDATA walkStackFrames(J9VMThread *currentThread, J9StackWalkState *walkState)
{
UDATA rc = (walkState->walkThread->privateFlags & J9_PRIVATE_FLAGS_STACK_CORRUPT) ? J9_STACKWALK_RC_STACK_CORRUPT : J9_STACKWALK_RC_NONE;
UDATA rc = J9_STACKWALK_RC_NONE;
UDATA walkRC = 0;
J9Method * nextLiterals;
UDATA * nextA0;
UDATA savedFlags = walkState->flags;
Expand All @@ -120,9 +151,15 @@ UDATA walkStackFrames(J9VMThread *currentThread, J9StackWalkState *walkState)
walkState->flags &= ~J9_STACKWALK_RESUME;
goto resumeInterpreterWalk;
}
if (currentThread != NULL) {

walkState->loopBreaker = 0;
if (NULL != currentThread) {
oldState = currentThread->activeWalkState;
currentThread->activeWalkState = walkState;
if (J9_ARE_ANY_BITS_SET(currentThread->privateFlags2, J9_PRIVATE_FLAGS2_ASYNC_GET_CALL_TRACE)) {
/* Add one because walkFrames decrements loopBreaker and bails when it reaches 0 */
walkState->loopBreaker = maxFramesOnStack(walkState) + 1;
}
}

walkState->javaVM = walkState->walkThread->javaVM;
Expand Down Expand Up @@ -330,7 +367,9 @@ UDATA walkStackFrames(J9VMThread *currentThread, J9StackWalkState *walkState)

/* Walk the frame */

if (walkFrame(walkState) != J9_STACKWALK_KEEP_ITERATING) {
walkRC = walkFrame(walkState);
if (J9_STACKWALK_KEEP_ITERATING != walkRC) {
rc = walkRC;
goto terminationPoint;
}
resumeInterpreterWalk:
Expand All @@ -342,7 +381,9 @@ UDATA walkStackFrames(J9VMThread *currentThread, J9StackWalkState *walkState)
#ifdef J9VM_INTERP_NATIVE_SUPPORT
if (walkState->frameFlags & J9_STACK_FLAGS_JIT_TRANSITION_TO_INTERPRETER_MASK) {
resumeJitWalk:
if (jitWalkStackFrames(walkState) != J9_STACKWALK_KEEP_ITERATING) {
walkRC = jitWalkStackFrames(walkState);
if (J9_STACKWALK_KEEP_ITERATING != walkRC) {
rc = walkRC;
goto terminationPoint;
}
walkState->decompilationRecord = NULL;
Expand Down Expand Up @@ -400,12 +441,23 @@ UDATA walkStackFrames(J9VMThread *currentThread, J9StackWalkState *walkState)
currentThread->activeWalkState = oldState;
}

if (J9_ARE_ANY_BITS_SET(walkState->walkThread->privateFlags, J9_PRIVATE_FLAGS_STACK_CORRUPT)) {
rc = J9_STACKWALK_RC_STACK_CORRUPT;
}

return rc;
}


UDATA walkFrame(J9StackWalkState * walkState)
{
if (0 != walkState->loopBreaker) {
walkState->loopBreaker -= 1;
if (0 == walkState->loopBreaker) {
return J9_STACKWALK_RC_STACK_CORRUPT;
}
}

if (walkState->flags & J9_STACKWALK_VISIBLE_ONLY) {

if ((((UDATA) walkState->pc == J9SF_FRAME_TYPE_NATIVE_METHOD) || ((UDATA) walkState->pc == J9SF_FRAME_TYPE_JNI_NATIVE_METHOD)) && !(walkState->flags & J9_STACKWALK_INCLUDE_NATIVES)) {
Expand Down Expand Up @@ -519,38 +571,17 @@ UDATA walkFrame(J9StackWalkState * walkState)
static UDATA allocateCache(J9StackWalkState * walkState)
{
PORT_ACCESS_FROM_WALKSTATE(walkState);
UDATA * endOfStack = walkState->walkThread->stackObject->end;
UDATA framesPresent = 0;
UDATA framesPresent = maxFramesOnStack(walkState);
UDATA cacheElementSize = 0;
UDATA cacheSize = 0;
UDATA * stackStart = J9_LOWEST_STACK_SLOT(walkState->walkThread);
UDATA * sp = walkState->walkThread->sp;

if (J9_ARE_NO_BITS_SET(walkState->flags, J9_STACKWALK_NO_ERROR_REPORT)) {
#if defined(J9VM_INTERP_STACKWALK_TRACING)
Assert_VRB_true(sp >= stackStart);
Assert_VRB_true(sp <= endOfStack);
#else /* J9VM_INTERP_STACKWALK_TRACING */
Assert_VM_true(sp >= stackStart);
Assert_VM_true(sp <= endOfStack);
#endif /* J9VM_INTERP_STACKWALK_TRACING */
}

framesPresent = (endOfStack - sp) / J9_STACKWALK_MIN_FRAME_SLOTS;

if (walkState->flags & J9_STACKWALK_CACHE_PCS) ++cacheElementSize;
if (walkState->flags & J9_STACKWALK_CACHE_CPS) ++cacheElementSize;
if (walkState->flags & J9_STACKWALK_CACHE_METHODS) ++cacheElementSize;

cacheSize = framesPresent * cacheElementSize;
#ifdef J9VM_INTERP_NATIVE_SUPPORT
if (walkState->walkThread->javaVM->jitConfig) {
if (!(walkState->flags & J9_STACKWALK_SKIP_INLINES)) {
/* computations above assume 1 cacheElement per frame, in reality there may be (maxInlinedMethods + 1) elements per frame */
cacheSize *= (walkState->walkThread->javaVM->jitConfig->maxInlineDepth + 1);
}
}
#endif

if ((walkState != walkState->walkThread->stackWalkState) || ((UDATA) (sp - stackStart) < cacheSize)
#if defined (J9VM_INTERP_VERBOSE) || defined (J9VM_PROF_EVENT_REPORTING)
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