Messages in this thread | | | Date | Fri, 27 Oct 2017 22:04:47 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH 02/18] x86/asm/64: Split the iret-to-user and iret-to-kernel paths |
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On Thu, Oct 26, 2017 at 01:26:34AM -0700, Andy Lutomirski wrote: > These code paths will diverge soon. > > Signed-off-by: Andy Lutomirski <luto@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...
> + RESTORE_EXTRA_REGS > + RESTORE_C_REGS > + REMOVE_PT_GPREGS_FROM_STACK 8 > + INTERRUPT_RETURN > + > > /* Returning to kernel space */ > retint_kernel: > @@ -632,11 +644,13 @@ retint_kernel: > */ > TRACE_IRQS_IRETQ > > -/* > - * At this label, code paths which return to kernel and to user, > - * which come from interrupts/exception and from syscalls, merge. > - */ > -GLOBAL(restore_regs_and_iret) > +GLOBAL(restore_regs_and_return_to_kernel) > +#ifdef CONFIG_DEBUG_ENTRY > + testl $3, CS(%rsp) > + jz 1f > + ud2 > +1: > +#endif
I guess here too, as a sanity-check. TEST and Jcc should be very cheap compared to everything else jumping-through-hoops we'll be doing :-\
-- Regards/Gruss, Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --
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