[9] RFR(L) 8158168: SIGSEGV: CollectedHeap::fill_with_objects(HeapWord*, unsigned long, bool)+0xa8 (original) (raw)

dean.long at oracle.com dean.long at oracle.com
Tue Mar 21 18:47:35 UTC 2017

On 3/21/17 9:37 AM, Vladimir Ivanov wrote:

and webrev.2 with it removed:

http://cr.openjdk.java.net/~dlong/8158168/webrev.2/ Thanks, Dean. I started with webrev.2 and tried to minimize the changes. I ended up with the following version: http://cr.openjdk.java.net/~vlivanov/dlong/8158168/webrev.00/

Thanks. The reason I didn't go with that approach from the beginning is because I couldn't convince myself that I could find all the missing bounds checks, and I wanted an interface to test against. With the bounds checks in AbstractStringBuilder, it is very hard to test all the possible race conditions, because some of the race conditions only happen when an ASB field changes half-way through the method.

Some clarifications:

============ src/java.base/share/classes/java/lang/String.java: The bounds check is needed only in String.nonSyncContentEquals when it extracts info from AbstractStringBuilder. I don't see how out of bounds access can happen in String.contentEquals: if (n != length()) { return false; } ... for (int i = 0; i < n; i++) { if (StringUTF16.getChar(val, i) != cs.charAt(i)) {

OK.

============ src/java.base/share/classes/java/lang/StringConcatHelper.java:

I think bounds checks in StringConcatHelper.prepend() are skipped intentionally, since java.lang.invoke.StringConcatFactory constructs method handle chains which already contain bounds checks: array length is precomputed based on argument values and all accesses are guaranteed to be in bounds.

This is calling the trusted version of getChars() with no bounds checks. It was a little more obvious when I had the Trusted inner class.

============ src/java.base/share/classes/java/lang/StringUTF16.java:

+ static void putChar(byte[] val, int index, int c) { + assert index >= 0 && index < length(val) : "Trusted caller missed bounds check"; Unfortunately, asserts can affect inlining decisions (since they increase bytecode size). In order to minimize possible performance impact, I suggest to remove them from the fix targeting 9.

Sure.

============ private static int indexOfSupplementary(byte[] value, int ch, int fromIndex, int max) { if (Character.isValidCodePoint(ch)) { final char hi = Character.highSurrogate(ch); final char lo = Character.lowSurrogate(ch); + checkBoundsBeginEnd(fromIndex, max, value);

The check is redundant here. fromIndex & max are always inbounds by construction: public static int indexOf(byte[] value, int ch, int fromIndex) { int max = value.length >> 1; if (fromIndex < 0) {_ _fromIndex = 0;_ _} else if (fromIndex >= max) { // Note: fromIndex might be near -1>>>1. return -1; } ... return indexOfSupplementary(value, ch, fromIndex, max);

OK.

============ I moved bounds checks from StringUTF16.lastIndexOf/indexOf to ABS.indexOf/lastIndexOf. I think it's enough to do range check on ABS.value & ABS.count. After that, all accesses should be inbounds by construction (in String.indexOf/lastIndexOf):

jdk/src/java.base/share/classes/java/lang/StringUTF16.java: static int lastIndexOf(byte[] src, byte srcCoder, int srcCount, String tgtStr, int fromIndex) { int rightIndex = srcCount - tgtCount; if (fromIndex > rightIndex) { fromIndex = rightIndex; } if (fromIndex < 0) {_ _return -1;_ _}_ _jdk/src/java.base/share/classes/java/lang/StringUTF16.java:_ _public static int lastIndexOf(byte[] src, int srcCount,_ _byte[] tgt, int tgtCount, int_ _fromIndex) {_ _int min = tgtCount - 1;_ _int i = min + fromIndex;_ _int strLastIndex = tgtCount - 1;_ _char strLastChar = getChar(tgt, strLastIndex);_ _startSearchForLastChar:_ _while (true) {_ _while (i >= min && getChar(src, i) != strLastChar) { There are 2 places: * getChar(tgt, strLastIndex) => getChar(tgt, tgtCount-1) - inbound * getChar(src, i); i in [ min; min+fromIndex ] min = tgtCount - 1 rightIndex = srcCount - tgtCount fromIndex <= rightIndex_ _0 <= min + fromIndex <= min + rightIndex == (tgtCount - 1)_ _+ (srcCount - tgtCount) == srcCount - 1_ _Hence, should be covered by the check on count & value:_ _public int lastIndexOf(String str, int fromIndex) {_ _+ byte[] value = this.value;_ _+ int count = this.count;_ _+ byte coder = this.coder;_ _+ checkIndex(count, value.length >> coder); return String.lastIndexOf(value, coder, count, str, fromIndex); }

OK, I will go with your version if it's OK with Sherman.

dl

Best regards, Vladimir Ivanov

On 3/17/17 5:58 AM, Vladimir Ivanov wrote:

I have the same concern. Can we fix the immediate problem in 9 and integrate verification logic in 10?

OK, Tobias is suggesting having verification logic only inside the intrinsics. Are you suggesting removing that as well? Yes and put them back in 10. I'm OK with removing all the verification, but that won't reduce the library changes much. I could undo the renaming to Trusted.getChar, but we would still have the bounds checks moved into StringUTF16. I suggest to go with a point fix for 9: just add missing range checks.

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