On Thu, Nov 02, 2017 at 12:58:59AM -0700, Andy Lutomirski wrote:
> These code paths will diverge soon.
>
> Signed-off-by: Andy Lutomirski <l...@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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