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?
