RFR: 8279545: Buffer overrun in reverse_words of sharedRuntime_x86_64.cpp:3517

[Coleen Phillimore]

On Wed, 12 Jan 2022 18:21:52 GMT, Harold Seigel <hseigel at openjdk.org> wrote:

> Please review this small fix to prevent a potential integer overflow that can cause a buffer overrun.  The fix was tested with Mach5 tiers 1-2 on Linux, Mac OS, and Windows, Mach5 tiers 3-5 on Linux x64, and Mach5 builds of the JDK on PPC and S390.
> 
> Thanks, Harold

src/hotspot/cpu/ppc/sharedRuntime_ppc.cpp line 3249:

> 3247:   // overflow. 512 jints corresponds to an 16384-bit integer and
> 3248:   // will use here a total of 6k bytes of stack space.
> 3249:   guarantee(longwords <= 341, "must be");

I was mystified about this number.  Can you make this instead like:

int thing = sizeof (unsigned long) * 3;
guarantee(longwords <= 8192 / thing, "must be");

Or is division just as unsafe?

Should this be uint64_t, not long ?  Or change it to julong if it's a small change to match the x86 version.

-------------

PR: https://git.openjdk.java.net/jdk/pull/7053