On Wed, Feb 14, 2018 at 08:39:11AM +0100, Ingo Molnar wrote:
>
> * Dave Hansen <dave.han...@intel.com> wrote:
>
> > On 02/13/2018 06:27 PM, Josh Poimboeuf wrote:
> > > --- a/arch/x86/entry/entry_64.S
> > > +++ b/arch/x86/entry/entry_64.S
> > > @@ -1167,10 +1167,10 @@ ENTRY(paranoid_exit)
> > > UNWIND_HINT_REGS
> > > DISABLE_INTERRUPTS(CLBR_ANY)
> > > TRACE_IRQS_OFF_DEBUG
> > > + RESTORE_CR3 scratch_reg=%r15 save_reg=%r14
> > > testl %ebx, %ebx /* swapgs needed? */
> > > jnz .Lparanoid_exit_no_swapgs
> > > TRACE_IRQS_IRETQ
> > > - RESTORE_CR3 scratch_reg=%rbx save_reg=%r14
> > > SWAPGS_UNSAFE_STACK
> > > jmp .Lparanoid_exit_restore
> > > .Lparanoid_exit_no_swapgs:
> >
> > TRACE_IRQS_* call non-entry functions that are not mapped by the user
> > CR3. How can this possibly work? What am I missing?
>
> How about something like the patch below? (Totally untested)
>
> Thanks,
>
> Ingo
> ---
> arch/x86/entry/entry_64.S | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index cd216c9431e1..8971bd64d515 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -1175,6 +1175,7 @@ ENTRY(paranoid_exit)
> jmp .Lparanoid_exit_restore
> .Lparanoid_exit_no_swapgs:
> TRACE_IRQS_IRETQ_DEBUG
> + RESTORE_CR3 scratch_reg=%rbx save_reg=%r14
> .Lparanoid_exit_restore:
> jmp restore_regs_and_return_to_kernel
> END(paranoid_exit)
Dave was right, my patch was obviously bogus. I couldn't figure out a
real reproducer, so I made an artificial one (see below) and can confirm
that your patch fixes it.
I would resubmit the patch, but now you're the author, so I'm not sure
how that works with the SOB.
Feel free to add my
Reported-and-tested-by: Josh Poimboeuf <jpoim...@redhat.com>
Thanks!
-------------
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 68c95a09b48d..c181eb23109b 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -325,6 +325,8 @@ syscall_return_via_sysret:
*/
SWITCH_TO_USER_CR3_STACK scratch_reg=%rdi
+ int3
+
popq %rdi
popq %rsp
USERGS_SYSRET64
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 3d9b2308e7fa..74fabcdf6c36 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -605,6 +605,8 @@ dotraplinkage void notrace do_int3(struct pt_regs *regs,
long error_code)
goto exit;
#endif
+ goto exit;
+
if (notify_die(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
SIGTRAP) == NOTIFY_STOP)
goto exit;
