At Mon, 23 Mar 2015 12:32:54 -0700, Andy Lutomirski wrote: > > We currently have a race: if we're preempted during syscall exit, we > can fail to process syscall return work that is queued up while > we're preempted in ret_from_sys_call after checking ti.flags. > > Fix it by disabling interrupts before checking ti.flags. > > Fixes: 96b6352c1271 x86_64, entry: Remove the syscall exit audit and schedule > optimizations > Reported-by: Stefan Seyfried <stefan.seyfr...@googlemail.com> > Reported-by: Takashi Iwai <ti...@suse.de>
I tested the patch again and confirmed that it works with the latest Linus tree. Tested-by: Takashi Iwai <ti...@suse.de> thanks, Takashi > Signed-off-by: Andy Lutomirski <l...@kernel.org> > --- > > Ingo, I don't understand the LOCKDEP_SYS_EXIT stuff. Can you take a quick > look to confirm that it's okay to call it more than once? > > arch/x86/kernel/entry_64.S | 18 ++++++++++++++---- > 1 file changed, 14 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S > index 1d74d161687c..2babb393915e 100644 > --- a/arch/x86/kernel/entry_64.S > +++ b/arch/x86/kernel/entry_64.S > @@ -364,12 +364,21 @@ system_call_fastpath: > * Has incomplete stack frame and undefined top of stack. > */ > ret_from_sys_call: > - testl $_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET) > - jnz int_ret_from_sys_call_fixup /* Go the the slow path */ > - > LOCKDEP_SYS_EXIT > DISABLE_INTERRUPTS(CLBR_NONE) > TRACE_IRQS_OFF > + > + /* > + * We must check ti flags with interrupts (or at least preemption) > + * off because we must *never* return to userspace without > + * processing exit work that is enqueued if we're preempted here. > + * In particular, returning to userspace with any of the one-shot > + * flags (TIF_NOTIFY_RESUME, TIF_USER_RETURN_NOTIFY, etc) set is > + * very bad. > + */ > + testl $_TIF_ALLWORK_MASK,TI_flags+THREAD_INFO(%rsp,RIP-ARGOFFSET) > + jnz int_ret_from_sys_call_fixup /* Go the the slow path */ > + > CFI_REMEMBER_STATE > /* > * sysretq will re-enable interrupts: > @@ -386,7 +395,7 @@ ret_from_sys_call: > > int_ret_from_sys_call_fixup: > FIXUP_TOP_OF_STACK %r11, -ARGOFFSET > - jmp int_ret_from_sys_call > + jmp int_ret_from_sys_call_irqs_off > > /* Do syscall tracing */ > tracesys: > @@ -432,6 +441,7 @@ tracesys_phase2: > GLOBAL(int_ret_from_sys_call) > DISABLE_INTERRUPTS(CLBR_NONE) > TRACE_IRQS_OFF > +int_ret_from_sys_call_irqs_off: > movl $_TIF_ALLWORK_MASK,%edi > /* edi: mask to check */ > GLOBAL(int_with_check) > -- > 2.3.0 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
