From: Rob Gardner <rob.gardner@xxxxxxxxxx> Date: Wed, 23 Dec 2015 10:31:01 -0700 > On 12/23/2015 09:21 AM, David Miller wrote: >> From: Rob Gardner <rob.gardner@xxxxxxxxxx> >> Date: Tue, 22 Dec 2015 23:24:49 -0700 >> >>> Short story: Exception handlers used by some copy_to_user() and >>> copy_from_user() functions do not diligently clean up floating point >>> register usage, and this can result in a user process seeing invalid >>> values in floating point registers. This sometimes makes the process >>> fail. >> Can you show me a specific example where the FPU register contents >> actually matter? >> >> When we are copying to or from userspace, we are in a most of the time >> system call, and for that specific case all FPU registers are volatile >> across the system call. >> >> I guess it might matter for the perf stack backtrace stuff. >> > > It does matter for the perf stack backtrace case. Running "perf record > -g ..." can cause random processes to experience FP register > corruption. Most of the time this is not noticed, but once in a while > it can cause a process to get incorrect results or corrupted data. > > This bug seriously affects system stability when using perf, and was > discovered while studying the plethora of perf problems. Great, thanks for the info. I'll do some testing here and apply this to the sparc GIT tree. -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
