Re: [lkp-robot] [x86/kconfig] 81d3871900: BUG:unable_to_handle_kernel

[Josh Poimboeuf <jpoimboe@redhat.com>]

On Fri, Oct 13, 2017 at 04:56:43PM +0300, Andrey Ryabinin wrote:
> On 10/13/2017 07:45 AM, Josh Poimboeuf wrote:
> > On Thu, Oct 12, 2017 at 12:05:04PM -0500, Christopher Lameter wrote:
> >> On Wed, 11 Oct 2017, Josh Poimboeuf wrote:
> >>
> >>> I failed to add the slab maintainers to CC on the last attempt.  Trying
> >>> again.
> >>
> >>
> >> Hmmm... Yea. SLOB is rarely used and tested. Good illustration of a simple
> >> allocator and the K&R mechanism that was used in the early kernels.
> >>
> >>>> Adding the slub maintainers.  Is slob still supposed to work?
> >>
> >> Have not seen anyone using it in a decade or so.
> >>
> >> Does the same config with SLUB and slub_debug on the commandline run
> >> cleanly?
> >>
> >>>> I have no idea how that crypto panic could could be related to slob, but
> >>>> at least it goes away when I switch to slub.
> >>
> >> Can you run SLUB with full debug? specify slub_debug on the commandline or
> >> set CONFIG_SLUB_DEBUG_ON
> > 
> > Oddly enough, with CONFIG_SLUB+slub_debug, I get the same crypto panic I
> > got with CONFIG_SLOB.  The trapping instruction is:
> > 
> >   vmovdqa 0x140(%rdi),%xmm0
> 
> 
> It's unaligned access. Look at %rdi. vmovdqa requires 16-byte alignment.
> Apparently, something fed kmalloc()'ed data here. But kmalloc() guarantees only sizeof(unsigned long)
> alignment. slub_debug changes slub's objects layout, so what happened to be 16-bytes aligned
> without slub_debug, may become 8-byte aligned with slub_debg on.
> 
>    
> > I'll try to bisect it tomorrow.  It at least goes back to v4.10.
> 
> Probably no point. I bet this bug always was here (since this code added).
> 
> This could be fixed by s/vmovdqa/vmovdqu change like bellow, but maybe the right fix
> would be to align the data properly?
> 
> ---
>  arch/x86/crypto/sha256-mb/sha256_mb_mgr_flush_avx2.S | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/crypto/sha256-mb/sha256_mb_mgr_flush_avx2.S b/arch/x86/crypto/sha256-mb/sha256_mb_mgr_flush_avx2.S
> index 8fe6338bcc84..7fd5d9b568c7 100644
> --- a/arch/x86/crypto/sha256-mb/sha256_mb_mgr_flush_avx2.S
> +++ b/arch/x86/crypto/sha256-mb/sha256_mb_mgr_flush_avx2.S
> @@ -155,8 +155,8 @@ LABEL skip_ %I
>  .endr
>  
>  	# Find min length
> -	vmovdqa _lens+0*16(state), %xmm0
> -	vmovdqa _lens+1*16(state), %xmm1
> +	vmovdqu _lens+0*16(state), %xmm0
> +	vmovdqu _lens+1*16(state), %xmm1
>  
>  	vpminud %xmm1, %xmm0, %xmm2		# xmm2 has {D,C,B,A}
>  	vpalignr $8, %xmm2, %xmm3, %xmm3	# xmm3 has {x,x,D,C}
> @@ -176,8 +176,8 @@ LABEL skip_ %I
>  	vpsubd	%xmm2, %xmm0, %xmm0
>  	vpsubd	%xmm2, %xmm1, %xmm1
>  
> -	vmovdqa	%xmm0, _lens+0*16(state)
> -	vmovdqa	%xmm1, _lens+1*16(state)
> +	vmovdqu	%xmm0, _lens+0*16(state)
> +	vmovdqu	%xmm1, _lens+1*16(state)
>  
>  	# "state" and "args" are the same address, arg1
>  	# len is arg2
> -- 
> 2.13.6

Makes sense.  I can confirm that the above patch fixes the panic.

-- 
Josh

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