On Sat, 2020-07-18 at 15:41 -0700, Dave Hansen wrote: > On 7/18/20 11:24 AM, Yu-cheng Yu wrote: > > On Sat, 2020-07-18 at 11:00 -0700, Andy Lutomirski wrote: > > > On Sat, Jul 18, 2020 at 10:58 AM Yu-cheng Yu <[email protected]> > > > wrote: > > > > Hi, > > > > > > > > My shadow stack tests start to have random shadow stack pointer > > > > corruption after > > > > v5.7 (excluding). The symptom looks like some locking issue or the > > > > kernel is > > > > confused about which CPU a task is on. In later tip/master, this can be > > > > triggered by creating two tasks and each does continuous > > > > pthread_create()/pthread_join(). If the kernel has max_cpus=1, the > > > > issue goes > > > > away. I also checked XSAVES/XRSTORS, but this does not seem to be an > > > > issue > > > > coming from there. > > > > > > What do you mean "shadow stack pointer corruption"? Is SSP itself > > > corrupt while running in the kernel? Is one of the MSRs getting > > > corrupted? Is the memory to which the shadow stack points getting > > > corrupted? Is the CPU rejecting an attempt to change SSP? > > > > What I see is, a new thread after ret_from_fork() and iret back to ring-3, > > its shadow stack pointer (MSR_IA32_PL3_SSP) is corrupted. > > Does corrupt mean random? Or is it a valid stack address, just not for > _this_ thread? Or NULL? Or is it a kernel address? Have you tried > tracing *ALL* the WRMSR's and XRSTOR's that write to the MSR?
When a shadow stack address is changed, the address appears to be other task's. I traced all WRMSR's and XRSTOR's. I also verified there have not been any XRSTORS from a wrong buffer. When rc6 is tagged, I will re-base, test, and share current patches.
