On Sat, Jul 18, 2020 at 11:25 AM Yu-cheng Yu <[email protected]> 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. > > >
This is going to be impossible to diagnose, given that the upstream kernel doesn't know about these MSRs at all. If you point to a git tree, maybe I can spot the issue.
