| Summary: | [1.36] SIGILL on accessing sha256 on some CPUs | ||
|---|---|---|---|
| Product: | Busybox | Reporter: | Tonis Tiigi <tonistiigi> |
| Component: | Other | Assignee: | unassigned |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | admwiggin+busyboxbugs, busybox-cvs, vda.linux |
| Priority: | P5 | ||
| Version: | unspecified | ||
| Target Milestone: | --- | ||
| Hardware: | All | ||
| OS: | Linux | ||
| Host: | Target: | ||
| Build: | |||
| Attachments: | patch which changes the sha extensions detection | ||
|
Description
Tonis Tiigi
2023-01-08 20:30:06 UTC
There has been some related discussion on the mailing list since this was opened, FWIW: - http://lists.busybox.net/pipermail/busybox/2023-January/090113.html - http://lists.busybox.net/pipermail/busybox/2023-March/090188.html - http://lists.busybox.net/pipermail/busybox/2023-March/090190.html - http://lists.busybox.net/pipermail/busybox/2023-March/090192.html Created attachment 9521 [details]
patch which changes the sha extensions detection
Intel has a documented C function (with inline assembly) to check for the SHA processor extensions: <https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sha-extensions.html#inpage-nav-5> ... in their CheckForIntelShaExtensions function after the CPUID call, the relevant bit is: > // Intel® SHA Extensions feature bit is EBX[29] > return ((b >> 29) & 1); BusyBox v1.36.0 seems to perform this check differently: shaNI = ((ebx >> 29) << 1) - 1; if (shaNI > 0) ... I was able to make the sha256sum function work on 8272CL by applying the attached patch. In one of my projects we recently stumbled for this issue (sha256sum running in Illegal instruction) as well and this project is using buildroot/busybox with latest busybox 1.36. See here for the related bugreport on github: https://github.com/jens-maus/RaspberryMatic/issues/2309 Too me this ready like this might be the exact same thing and even thought only affects very rarely some users with some CPU/setup types, I do feel this might be related as well. Any chance to get this patch merged if it really solves this issue? In your patch: - shaNI = ((ebx >> 29) << 1) - 1; + shaNI = ((ebx >> 29) & 1); This will set shaNI to 0 if bit is not set, instead of -1. Which will make sha1_begin/sha256_begin check it again on every single call. CPUID insn takes something like 300 cycles. Fixed in git. https://git.busybox.net/busybox/commit/?id=bd76b75f72f717150b909e8c64edfda725cabe11 - shaNI = ((ebx >> 29) << 1) - 1; + shaNI = ((ebx >> 28) & 2) - 1; /* bit 29 -> 1 or -1 */ Will be released in June. |