netdev - Re: Another regression in the af_alg series (s390x-specific)

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Date: Wed, 26 Jul 2023 16:38:32 +0100
From: David Howells <dhowells@...hat.com>
To: Ondrej Mosnáček <omosnacek@...il.com>
Cc: dhowells@...hat.com,
    Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
    Herbert Xu <herbert@...dor.apana.org.au>,
    Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
    regressions@...ts.linux.dev,
    Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Another regression in the af_alg series (s390x-specific)

Well, I can reproduce it fairly easily.  It seems to be:

	static inline void scatterwalk_start(struct scatter_walk *walk,
					     struct scatterlist *sg)
	{
		walk->sg = sg;
		walk->offset = sg->offset;  <----
	}

Presumably sg is rubbish.

Dump of assembler code for function gcm_walk_start:
   0x0000000000000038 <+0>:     jgnop   0x38 <gcm_walk_start>
   0x000000000000003e <+6>:     xc      8(64,%r2),8(%r2)
   0x0000000000000044 <+12>:    st      %r4,32(%r2)
   0x0000000000000048 <+16>:    stg     %r3,0(%r2)
   0x000000000000004e <+22>:    l       %r1,8(%r3)
   0x0000000000000052 <+26>:    st      %r1,8(%r2)
   0x0000000000000056 <+30>:    jg      0x56 <gcm_walk_start+30>

I'm don't know much about s390x assembly, but I'm guessing %r2 has "walk" and
%r3 has "sg".

AS:0000000116d50007 R3:0000000000000024 
Fault in home space mode while using kernel ASCE.
Failing address: 0026070200000000 TEID: 0026070200000803
Unable to handle kernel pointer dereference in virtual kernel address space

Krnl GPRS: 000000000000000c 0000038000000310 00000380002a7938 0026070200000000
           0000000000000000 0000000115593cb4 0000000000000000 0000000000000010
           0000000100000000 000000017e984690 000000000000000c 0000000000000000
           000003ffaf12cf98 0000000000000000 000003ff7fc536ba 00000380002a77e0

I'm not sure what to make of the 0026070200000000.

David