[Bug 1951470] Re: webkit javascript segmentation fault
Dmitry Shachnev
1951470 at bugs.launchpad.net
Sat Nov 27 13:22:30 UTC 2021
I have uploaded Focal, Impish and Hirsute debdiffs, they are now waiting
for approval in review queues.
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https://bugs.launchpad.net/bugs/1951470
Title:
webkit javascript segmentation fault
Status in Ubuntu on IBM z Systems:
In Progress
Status in qtwebkit-opensource-src package in Ubuntu:
Fix Released
Status in qtwebkit-opensource-src source package in Focal:
In Progress
Status in qtwebkit-opensource-src source package in Hirsute:
In Progress
Status in qtwebkit-opensource-src source package in Impish:
In Progress
Status in qtwebkit-opensource-src source package in Jammy:
Fix Released
Bug description:
SRU Justification:
[Impact]
* WebKit Javascript engine is causing a segmentation fault on big
endian (s390x) systems.
* This happens for example when transferring an html to a pdf file
using wkhtmltopdf.
* The fix is relatively simple with changing loadisFromInstruction to loadpFromInstruction
in macro getProperty(slow), which solves this unpleasant situation.
* The JIT ocde is 32bit (even on 64bit systems),
hence is crucial to make sure the lower part of a 64bit value is taken on big endian systems.
[Test Plan]
* Testing is very straight forward by following these steps:
* install the following packages (incl. their dependencies):
$ sudo apt install libqt5webkit5 wkhtmltopdf
* create an html file like this:
$ vi index.html
$ cat index.html
<!doctype html>
<html lang="de">
<head>
</head>
<body>
<script src="min.js"></script>
</body>
</html>
* create a JavaScript file like this:
$ vi min.js
$ cat min.js
var i = Math.max
* call wkhtmltopdf to process the local files:
$ wkhtmltopdf --enable-local-file-access index.html test.pdf
* if it's broken one gets this output:
Loading page (1/2)
Segmentation fault (core dumped) ] 50%
and no pdf file was generated:
$ ls *.pdf
ls: cannot access '*.pdf': No such file or directory
* in case it's fixed one gets this output:
Loading page (1/2)
Printing pages (2/2)
Done
and a pdf file was generated and in placed in the current directory (with more than 0 bytes size):
$ ls -l ./*.pdf
-rw-rw-r-- 1 ubuntu ubuntu 1339 Nov 24 11:48 ./test.pdf
[Where problems could occur]
* While this issue only affects big endian systems (like s390x),
a bad fix may have an impact on little endian systems, too
for example in case the wrong function got used in the macro.
* But loadpFromInstruction is known to work for LE and BE systems;
* and on top cross-architecture builds were done:
https://launchpad.net/~fheimes/+archive/ubuntu/lp1951470
* and tested on s390x (if the fix works) and on non-s390x (regression
testing).
* The changes are otherwise very limited, just:
macro getProperty(slow)
- loadisFromInstruction(6, t1)
+ loadpFromInstruction(6, t1)
hence I think there is not much more to say.
[Other Info]
* The maintainer of the Debian packages (Dmitry Shachnev)
is going to add this to the Debian package, too.
* This issue affects Ubuntu jammy, impish, hirsute and focal - SRUs
are ongoing.
* The issue does not occur with the very latest upstream version anymore,
and was fixed in a similar way as part of a commit
that fixes numerous other CLoop issues on top:
"Fix all CLoop JSC test failures (including some LLInt bugs due to recent bytecode format change)."
commit 3fdde71c7d95d758a61fcbc4c58168616794c102
__________
== Comment: #0 - Andreas Krebbel <Andreas.Krebbel at de.ibm.com> - 2021-11-15 09:29:44 ==
---Problem Description---
Segmentation fault from WebKit Javascript engine
Contact Information = andreas.krebbel at de.ibm.com
---uname output---
Linux 193438490afd 5.8.15-301.fc33.s390x #1 SMP Thu Oct 15 15:55:57 UTC 2020 s390x s390x s390x GNU/Linux
Machine Type = IBM Z
---Debugger---
A debugger is not configured
---Steps to Reproduce---
index.html:
<!doctype html>
<html lang="de">
<head>
</head>
<body>
<script src="min.js"></script>
</body>
</html>
min.js:
var i = Math.max
wkhtmltopdf index.html test.pdf
QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-root'
Loading page (1/2)
Segmentation fault (core dumped) ] 17%
Userspace tool common name: wkhtmltopdf
The userspace tool has the following bit modes: 64
Userspace rpm: libqt5webkit5
Userspace tool obtained from project website: na
*Additional Instructions for andreas.krebbel at de.ibm.com:
-Attach ltrace and strace of userspace application.
== Comment: #1 - Andreas Krebbel <Andreas.Krebbel at de.ibm.com> - 2021-11-15 09:44:04 ==
In CodeBlock.cpp the code preparing the operands of op_get_from_scope writes the property offset as pointer size (hence 64 bit) value:
2141: instructions[i + 6].u.pointer =
reinterpret_cast<void*>(op.operand);
while the same slot is accessed later by the jitted code as 32 bit
integer:
macro getProperty(slow)
loadisFromInstruction(6, t1)
This fails on big endian targets since the integer access takes the
higher part of the 64 bit value.
Changing:
macro getProperty(slow)
loadisFromInstruction(6, t1)
to
macro getProperty(slow)
loadpFromInstruction(6, t1)
in llint/LowLevelInterpreter64.asm fixes the problem for me.
I could not reproduce the problem on Ubuntu 20.10. In upstream webkit
the problem got fixed as a side effect of a larger change but in the
end quite similar to the change I'm proposing. The value resides
somewhere else now but it is accessed as 64 bit value in getProperty:
macro getProperty()
loadp OpGetFromScope::Metadata::m_operand[t5], t1
If you have the jsc binary from the webkit package available the
problem can be reproduced with just 'jsc -e "i=Math.min"'
== Comment: #2 - Andreas Krebbel <Andreas.Krebbel at de.ibm.com> -
2021-11-15 09:49:55 ==
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