Re: [PATCH] x86/paravirt: Add missing noinstr to arch_local*() helpers

Marco Elver
2020-08-05T16:56:30Z

On Wed, Aug 05, 2020 at 03:42PM +0200, peterz@infradead.org wrote:
> On Wed, Aug 05, 2020 at 03:26:29PM +0200, Marco Elver wrote:
> > Add missing noinstr to arch_local*() helpers, as they may be called from
> > noinstr code.
> >
> > On a KCSAN config with CONFIG_PARAVIRT=y, syzbot stumbled across corrupt
>
> Cute, so I've been working on adding objtool support for this a little:
>
> https://lkml.kernel.org/r/20200803143231.GE2674@hirez.programming.kicks-ass.net
>
> > diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> > index 3d2afecde50c..a606f2ba2b5e 100644
> > --- a/arch/x86/include/asm/paravirt.h
> > +++ b/arch/x86/include/asm/paravirt.h
> > @@ -760,27 +760,27 @@ bool __raw_callee_save___native_vcpu_is_preempted(long cpu);
> > ((struct paravirt_callee_save) { func })
> >
> > #ifdef CONFIG_PARAVIRT_XXL
> > -static inline notrace unsigned long arch_local_save_flags(void)
> > +static inline noinstr unsigned long arch_local_save_flags(void)
> > {
> > return PVOP_CALLEE0(unsigned long, irq.save_fl);
> > }
> >
> > -static inline notrace void arch_local_irq_restore(unsigned long f)
> > +static inline noinstr void arch_local_irq_restore(unsigned long f)
> > {
> > PVOP_VCALLEE1(irq.restore_fl, f);
> > }
> >
> > -static inline notrace void arch_local_irq_disable(void)
> > +static inline noinstr void arch_local_irq_disable(void)
> > {
> > PVOP_VCALLEE0(irq.irq_disable);
> > }
> >
> > -static inline notrace void arch_local_irq_enable(void)
> > +static inline noinstr void arch_local_irq_enable(void)
> > {
> > PVOP_VCALLEE0(irq.irq_enable);
> > }
> >
> > -static inline notrace unsigned long arch_local_irq_save(void)
> > +static inline noinstr unsigned long arch_local_irq_save(void)
> > {
> > unsigned long f;
> >
>
> Shouldn't we __always_inline those? They're going to be really small.

I can send a v2, and you can choose. For reference, though:

ffffffff86271ee0 <arch_local_save_flags>:
ffffffff86271ee0: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
ffffffff86271ee5: 48 83 3d 43 87 e4 01 cmpq $0x0,0x1e48743(%rip) # ffffffff880ba630 <pv_ops+0x120>
ffffffff86271eec: 00
ffffffff86271eed: 74 0d je ffffffff86271efc <arch_local_save_flags+0x1c>
ffffffff86271eef: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
ffffffff86271ef4: ff 14 25 30 a6 0b 88 callq *0xffffffff880ba630
ffffffff86271efb: c3 retq
ffffffff86271efc: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
ffffffff86271f01: 0f 0b ud2
ffffffff86271f03: 66 66 2e 0f 1f 84 00 data16 nopw %cs:0x0(%rax,%rax,1)
ffffffff86271f0a: 00 00 00 00
ffffffff86271f0e: 66 90 xchg %ax,%ax

[...]

ffffffff86271a90 <arch_local_irq_restore>:
ffffffff86271a90: 53 push %rbx
ffffffff86271a91: 48 89 fb mov %rdi,%rbx
ffffffff86271a94: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
ffffffff86271a99: 48 83 3d 97 8b e4 01 cmpq $0x0,0x1e48b97(%rip) # ffffffff880ba638 <pv_ops+0x128>
ffffffff86271aa0: 00
ffffffff86271aa1: 74 11 je ffffffff86271ab4 <arch_local_irq_restore+0x24>
ffffffff86271aa3: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
ffffffff86271aa8: 48 89 df mov %rbx,%rdi
ffffffff86271aab: ff 14 25 38 a6 0b 88 callq *0xffffffff880ba638
ffffffff86271ab2: 5b pop %rbx
ffffffff86271ab3: c3 retq
ffffffff86271ab4: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
ffffffff86271ab9: 0f 0b ud2
ffffffff86271abb: cc int3
ffffffff86271abc: cc int3
ffffffff86271abd: cc int3
ffffffff86271abe: cc int3
ffffffff86271abf: cc int3

[... and the rest looking of similar size.]

Thanks,
-- Marco