Re: [PATCH] powerpc: Enable UBSAN support

[Daniel Axtens <dja@axtens.net>]

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>> Have you tried running with KVM?

OK, I ran a UBSAN kvm guest on a UBSAN host and I ran trinity inside the
guest. It all appears to work as usual.

I really don't have the knowledge to determine what we should exclude,
but I'm very very happy to respin with a greater list of excludes if you
think that's a good idea.

Regards,
Daniel


>>
>> I'm wondering if we should be excluding some of the KVM code that runs in real mode, eg:
>>
>>   arch/powerpc/kvm/book3s_hv_rm_mmu.c
>>   arch/powerpc/kvm/book3s_hv_rm_xics.c
>>
>> And maybe some other bits.
>>
>> Also the early setup code, a/p/k/setup*.c might be dicey.
>
> My philosphy was just to copy the GCOV excludes, although you're right
> that perhaps we want to be more aggressive in excluding here given that
> the UBSAN handlers print a bunch of stuff. I'm happy to respin with
> further exclusions - they're really easy to add.
>
>> In all of the above it's probably OK unless you actually hit a warning at the
>> wrong point, so testing will probably not find problems. Although I guess we
>> could add some deliberatly incorrect code at certain points and check we
>> survive the warning.
>
> Yep. I'll run a kvm guest on an instrumented kernel and let you know
> what happens!
>
>>
>> Is there an easy way to spot the calls to UBSAN in the generated code?
>
> Yes - because of the handler functions, they're *really* easy to spot.
> Here's some assembly for GregorianDay():
>
>
> c00000000002924c:       6d 26 7e 48     bl      c00000000080b8b8 <__ubsan_handle_mul_overflow+0x8>
> c000000000029250:       00 00 00 60     nop
> c000000000029254:       38 fe ff 4b     b       c00000000002908c <GregorianDay+0xdc>
> c000000000029258:       8c ff 62 3c     addis   r3,r2,-116
> c00000000002925c:       01 00 a0 38     li      r5,1
> c000000000029260:       78 db 64 7f     mr      r4,r27
> c000000000029264:       50 9c 63 38     addi    r3,r3,-25520
> c000000000029268:       41 26 7e 48     bl      c00000000080b8a8 <__ubsan_handle_sub_overflow+0x8>
> c00000000002926c:       00 00 00 60     nop
> c000000000029270:       44 fe ff 4b     b       c0000000000290b4 <GregorianDay+0x104>
> c000000000029274:       8c ff 62 3c     addis   r3,r2,-116
> c000000000029278:       78 d3 45 7f     mr      r5,r26
> c00000000002927c:       e0 9c 63 38     addi    r3,r3,-25376
> c000000000029280:       19 26 7e 48     bl      c00000000080b898 <__ubsan_handle_add_overflow+0x8>
> c000000000029284:       00 00 00 60     nop
> c000000000029288:       94 fe ff 4b     b       c00000000002911c <GregorianDay+0x16c>
> c00000000002928c:       8c ff 62 3c     addis   r3,r2,-116
> c000000000029290:       78 f3 c4 7f     mr      r4,r30
> c000000000029294:       68 9c 63 38     addi    r3,r3,-25496
> c000000000029298:       b1 21 7e 48     bl      c00000000080b448 <__ubsan_handle_out_of_bounds+0x8>
> c00000000002929c:       00 00 00 60     nop
> c0000000000292a0:       20 fe ff 4b     b       c0000000000290c0 <GregorianDay+0x110>
> c0000000000292a4:       14 4a 24 7d     add     r9,r4,r9
> c0000000000292a8:       40 48 a4 7f     cmpld   cr7,r4,r9
> c0000000000292ac:       2c fe fd 41     bgt+    cr7,c0000000000290d8 <GregorianDay+0x128>
>
> You can see that there are lots of calls to __ubsan_handle_blah_blah
> inserted.
>
> Regards,
> Daniel
>
>>
>> cheers
>>
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