linux-kernel - Re: [PATCH 7/7] s390/vdso: Wire up getrandom() vdso implementation

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Message-ID: <20240913173206.30385-C-hca@linux.ibm.com>
Date: Fri, 13 Sep 2024 19:32:06 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: "Jason A. Donenfeld" <Jason@...c4.com>
Cc: Alexander Gordeev <agordeev@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Harald Freudenberger <freude@...ux.ibm.com>,
        Stefan Liebler <stli@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH 7/7] s390/vdso: Wire up getrandom() vdso implementation

On Fri, Sep 13, 2024 at 05:22:09PM +0200, Jason A. Donenfeld wrote:
> On Fri, Sep 13, 2024 at 05:13:28PM +0200, Jason A. Donenfeld wrote:
> > On Fri, Sep 13, 2024 at 03:05:43PM +0200, Heiko Carstens wrote:
> > > The vdso testcases vdso_test_getrandom and vdso_test_chacha pass.
> > 
> > I'm trying to cross compile this but I'm getting:
> > 
> >   CC       vdso_test_chacha
> > /home/zx2c4/Projects/random-linux/tools/testing/selftests/../../../tools/arch/s390/vdso/vgetrandom-chacha.S: Assembler messages:
> > /home/zx2c4/Projects/random-linux/tools/testing/selftests/../../../tools/arch/s390/vdso/vgetrandom-chacha.S:147: Error: Unrecognized opcode: `alsih'
> > 
> > Any idea what's up?
> 
> Looks like I needed `-march=arch9`. I can potentially rebuild my
> toolchains to do this by default, though, if that's a normal thing to
> have and this is just my toolchain being crappy. Or, if it's not a
> normal thing to have, do we need to add it to the selftests Makefile?

That needs to be fixed differently, since the kernel build would also
fail when building for z10. Could you squash the below fix into this
patch, please?

That way the compiler will still generate the correct code even if
compiled with a lower march flag. There is already a guard in place
(test_facility()), which prevents that this code will be executed if
the machine does not know the instruction.

So for the kernel itself including the vdso code, everything is
correct now. But similar checks are missing within vdso_test_chacha.c.
I'll provide something for that, so that the test case will be skipped
if the required instructions are missing, but not today.

diff --git a/arch/s390/kernel/vdso64/vgetrandom-chacha.S b/arch/s390/kernel/vdso64/vgetrandom-chacha.S
index ecd44cf0eaba..d802b0a96f41 100644
--- a/arch/s390/kernel/vdso64/vgetrandom-chacha.S
+++ b/arch/s390/kernel/vdso64/vgetrandom-chacha.S
@@ -144,7 +144,8 @@ SYM_FUNC_START(__arch_chacha20_blocks_nostack)
 .Lstoredone:
 
 	/* ++COPY3.COUNTER */
-	alsih	%r3,1
+	/* alsih %r3,1 */
+	.insn	rilu,0xcc0a00000000,%r3,1
 	alcr	%r3,%r1
 	VLVGG	COPY3,%r3,0