| Date | Thu, 2 Nov 2017 11:50:18 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v2 02/20] x86/asm/64: Split the iret-to-user and iret-to-kernel paths |
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On Thu, Nov 02, 2017 at 12:58:59AM -0700, Andy Lutomirski wrote: > These code paths will diverge soon. > > Signed-off-by: Andy Lutomirski <luto@kernel.org> > --- > arch/x86/entry/entry_64.S | 34 +++++++++++++++++++++++++--------- > arch/x86/entry/entry_64_compat.S | 2 +- > arch/x86/kernel/head_64.S | 2 +- > 3 files changed, 27 insertions(+), 11 deletions(-) > > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S > index afe1f403fa0e..07fe816f0d28 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 > 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 +612,20 @@ 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 > + /* Assert that pt_regs indicates user mode. */ > + testl $3, CS(%rsp) > + jnz 1f > + ud2 > +1: > +#endif
Here's me arguing in v2:
If these paths are slow and adding a TEST and a Jcc would give us the additional sanity-checking, then I don't see any downside to it.
-- Regards/Gruss, Boris.
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) --
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