On Fri, Oct 27, 2017 at 11:05 AM, Dave Hansen <[email protected]> wrote: > On 10/26/2017 01:26 AM, Andy Lutomirski wrote: >> +GLOBAL(restore_regs_and_return_to_usermode) >> +#ifdef CONFIG_DEBUG_ENTRY >> + testl $3, CS(%rsp) >> + jnz 1f >> + ud2 > > A nit from the mere mortals in the audience: Could we start commenting > or make a constant for the user segment bits in CS?
Yeah. We have such a define, but it's not currently usable from asm. Also, we can't do the obvious: testl $SEGMENT_RPL_MASK, ... jump_if_not_equal_to_KERNEL_RPL because that makes no sense in asm :( > > Also, it would be nice to explain what's going on here. Maybe: > > /* > * We think we are returning to the kernel. Check the > * registers we are about to restore and if we appear to > * be returning to userspace, do something that will cause > * a fault and hopefully an oops report. > */ > > Otherwise, I really like this change. It's really hard to figure out > what the context is in the entry assembly in a lot of cases. It's a > place where code reuse actually makes things harder to follow.
