KASAN issues with idle / hotplug area (was: Re: [PATCH v5sub1 7/8] arm64: move kernel image to base of vmalloc area)

[Mark Rutland]

On Wed, Feb 17, 2016 at 05:56:56PM +0000, Mark Rutland wrote:
> On Wed, Feb 17, 2016 at 05:01:11PM +0000, Mark Rutland wrote:
> > On Wed, Feb 17, 2016 at 02:39:51PM +0000, Mark Rutland wrote:
> > > Perhaps the simplest option is to not instrument invoke_psci_fn_* and
> > > psci_suspend_finisher. Do we have a per-function annotation to avoid
> > > KASAN instrumentation, like notrace? I need to investigate, but we may
> > > also need notrace for similar reasons.
> >
> > I came up with the patch below, per the reasoning above.
> > 
> > It _changes_ the KASAN splats (I see errors in tick_program_event rather
> > than find_busiest_group), but doesn't seem to get rid of them. I'm not
> > sure if I've missed something, or if we also have another latent issue.
> > 
> > Ideas?
> 
> I'd missed annotating __cpu_suspend_save. I've fixed that up locally
> (along with s/virt_to_phys/__virt_to_phys due to the inlining issue).

Thinking about it more, I shouldn't have to annotate __cpu_suspend_save,
as it returns (and hence should have cleaned up after itself).

Looking at the assembly, functions seem to get instrumented regardless
of the __no_sanitize_address annotation. The assembly of
__invoke_psci_fn_{smc,hvc} look identical, even if one has the
annotation and one does not.

In the case below, it looks like __invoke_psci_fn_hvc is storing to the
shadow area even though it's anotated with __no_sanitize_address.  Note
that the adrp symbol resolution is bogus; psci_to_linux_errno happens to
be at offset 0 in the as-yet unlinked psci.o object.

0000000000000420 <__invoke_psci_fn_hvc>:
 420:   d10283ff        sub     sp, sp, #0xa0
 424:   90000004        adrp    x4, 0 <psci_to_linux_errno>
 428:   91000084        add     x4, x4, #0x0
 42c:   90000005        adrp    x5, 0 <psci_to_linux_errno>
 430:   910000a5        add     x5, x5, #0x0
 434:   d2800007        mov     x7, #0x0                        // #0
 438:   a9017bfd        stp     x29, x30, [sp,#16]
 43c:   910043fd        add     x29, sp, #0x10
 440:   d2800006        mov     x6, #0x0                        // #0
 444:   a90253f3        stp     x19, x20, [sp,#32]
 448:   9100c3b3        add     x19, x29, #0x30
 44c:   d2dff214        mov     x20, #0xff9000000000            // #280993940373504
 450:   a90393a5        stp     x5, x4, [x29,#56]
 454:   f2fbfff4        movk    x20, #0xdfff, lsl #48
 458:   d343fe73        lsr     x19, x19, #3
 45c:   d2915664        mov     x4, #0x8ab3                     // #35507
 460:   f9001bf5        str     x21, [sp,#48]
 464:   f2a836a4        movk    x4, #0x41b5, lsl #16
 468:   8b140275        add     x21, x19, x20
 46c:   f9001ba4        str     x4, [x29,#48]
 470:   3204d3e4        mov     w4, #0xf1f1f1f1                 // #-235802127
 474:   b8346a64        str     w4, [x19,x20]
 478:   3204d7e4        mov     w4, #0xf3f3f3f3                 // #-202116109
 47c:   b9000aa4        str     w4, [x21,#8]
 480:   910143a4        add     x4, x29, #0x50
 484:   d2800005        mov     x5, #0x0                        // #0
 488:   f90003e4        str     x4, [sp]
 48c:   d2800004        mov     x4, #0x0                        // #0
 490:   94000000        bl      0 <arm_smccc_hvc>
 494:   f9402ba0        ldr     x0, [x29,#80]
 498:   910003bf        mov     sp, x29
 49c:   b8346a7f        str     wzr, [x19,x20]
 4a0:   b9000abf        str     wzr, [x21,#8]
 4a4:   a94153f3        ldp     x19, x20, [sp,#16]
 4a8:   f94013f5        ldr     x21, [sp,#32]
 4ac:   a8c97bfd        ldp     x29, x30, [sp],#144
 4b0:   d65f03c0        ret
 4b4:   d503201f        nop

For comparison, without KASAN __incoke_psci_fn_hvc looks like:

0000000000000280 <__invoke_psci_fn_hvc>:
 280:   d10103ff        sub     sp, sp, #0x40
 284:   d2800007        mov     x7, #0x0                        // #0
 288:   d2800006        mov     x6, #0x0                        // #0
 28c:   d2800005        mov     x5, #0x0                        // #0
 290:   a9017bfd        stp     x29, x30, [sp,#16]
 294:   910043fd        add     x29, sp, #0x10
 298:   910043a4        add     x4, x29, #0x10
 29c:   f90003e4        str     x4, [sp]
 2a0:   d2800004        mov     x4, #0x0                        // #0
 2a4:   94000000        bl      0 <arm_smccc_hvc>
 2a8:   910003bf        mov     sp, x29
 2ac:   f9400ba0        ldr     x0, [x29,#16]
 2b0:   a8c37bfd        ldp     x29, x30, [sp],#48
 2b4:   d65f03c0        ret

I also tried using __attribute__((no_sanitize_address)) directly, in
case there was some header issue, but that doesn't seem to be the case.

I'm using the Linaro 15.08 AArch64 GCC 5.1. Is anyone else able to
confirm whether they see the same? Does the same happen for x86?

Thanks,
Mark.