On Fri, Oct 27, 2017 at 1:04 PM, Borislav Petkov <b...@suse.de> wrote: > On Thu, Oct 26, 2017 at 01:26:34AM -0700, Andy Lutomirski wrote: >> These code paths will diverge soon. >> >> Signed-off-by: Andy Lutomirski <l...@kernel.org> >> --- >> arch/x86/entry/entry_64.S | 32 +++++++++++++++++++++++--------- >> arch/x86/entry/entry_64_compat.S | 2 +- >> arch/x86/kernel/head_64.S | 2 +- >> 3 files changed, 25 insertions(+), 11 deletions(-) >> >> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S >> index afe1f403fa0e..493e5e234d36 100644 >> --- a/arch/x86/entry/entry_64.S >> +++ b/arch/x86/entry/entry_64.S >> @@ -321,7 +321,7 @@ syscall_return_via_sysret: >> >> opportunistic_sysret_failed: >> SWAPGS >> - jmp restore_regs_and_iret >> + jmp restore_regs_and_return_to_usermode > > rstor_regs_ret_user > > still sounds pretty ok to me and it is shorter and it is using the > *RSTOR spelling the respective FPU insns use, so should be recognizable. :-) > > And the other one could be > > rstor_regs_ret_kernel > > of course. > >> END(entry_SYSCALL_64) >> >> ENTRY(stub_ptregs_64) >> @@ -423,7 +423,7 @@ ENTRY(ret_from_fork) >> call syscall_return_slowpath /* returns with IRQs disabled */ >> TRACE_IRQS_ON /* user mode is traced as IRQS on */ >> SWAPGS >> - jmp restore_regs_and_iret >> + jmp restore_regs_and_return_to_usermode >> >> 1: >> /* kernel thread */ >> @@ -612,7 +612,19 @@ GLOBAL(retint_user) >> call prepare_exit_to_usermode >> TRACE_IRQS_IRETQ >> SWAPGS >> - jmp restore_regs_and_iret >> + >> +GLOBAL(restore_regs_and_return_to_usermode) >> +#ifdef CONFIG_DEBUG_ENTRY >> + testl $3, CS(%rsp) > > testb > > ditto for the other spot. > >> + jnz 1f >> + ud2 >> +1: >> +#endif > > Why aren't we exploding here unconditionally? I mean, we don't want to > return with RPL != 3 CS for whatever reason...
Performance? I'll admit that both of these paths are extremely slow no matter what, but it's nice to get a real dump if we screw it up. I'll leave it as is for v2. Feel free to argue more in v2 :)
