On 9/23/20 3:47 PM, Andy Lutomirski wrote: > On Wed, Sep 23, 2020 at 3:20 PM Yu, Yu-cheng <[email protected]> wrote: >> On 9/23/2020 3:08 PM, Dave Hansen wrote: >>> On 9/23/20 3:06 PM, Yu, Yu-cheng wrote: >>>> I think I'll add a check here for (r + 8) >= TASK_SIZE_MAX. It is >>>> better than getting a fault. >>> There's also wrmsr_safe(). >>> >> Yes, thanks. >> >> Since I am going to change this to: >> >> fpu__prepare_write(), then write to the XSAVES area. >> >> The kernel does not expect XRSTORS to fail ("Bad FPU state detected..." >> message). So maybe still check the address first. > Surely there are plenty of ways to use ptrace() to poke garbage into > the FPU state. We should be able to handle this type of failure > somewhat gracefully.
Yeah, agreed. I'd much rather make XRSTORS able to #GP gracefully than teach the kernel exhaustively about every possible error condition it can encounter. We *might* want to do something like to preserve the warning if the task hasn't been ptrace'd, or had the memory buffer written to directly or tainted in another way.
