Messages in this thread |  | | Date | Sun, 1 Jan 2023 17:21:24 +0100 | From | "Jason A. Donenfeld" <> | Subject | Re: [PATCH v13 7/7] x86: vdso: Wire up getrandom() vDSO implementation |
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On Wed, Dec 21, 2022 at 03:27:04PM -0800, Eric Biggers wrote: > On Wed, Dec 21, 2022 at 03:23:27PM +0100, Jason A. Donenfeld wrote: > > diff --git a/arch/x86/entry/vdso/vgetrandom-chacha.S b/arch/x86/entry/vdso/vgetrandom-chacha.S > > new file mode 100644 > > index 000000000000..91fbb7ac7af4 > > --- /dev/null > > +++ b/arch/x86/entry/vdso/vgetrandom-chacha.S > > @@ -0,0 +1,177 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > +/* > > + * Copyright (C) 2022 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved. > > + */ > > + > > +#include <linux/linkage.h> > > +#include <asm/frame.h> > > + > > +.section .rodata.cst16.CONSTANTS, "aM", @progbits, 16 > > +.align 16 > > +CONSTANTS: .octa 0x6b20657479622d323320646e61707865 > > +.text > > For simplicity, maybe leave off the section mergeability stuff and just have > plain ".section .rodata"?
I guess nothing is going to get merged anyway, so sure, why not.
> It would be worth mentioning in the function comment that none of the xmm > registers are callee-save. That was not obvious to me. I know that on arm64, > *kernel* code doesn't need to save/restore NEON registers, so it's not something > that arch/arm64/crypto/ does. But, it *is* needed in arm64 userspace code. So > I was worried that something similar would apply to x86_64, but it seems not.
I'll add a comment.
> > > + /* state1[0,1,2,3] = state1[0,3,2,1] */ > > + pshufd $0x39,state1,state1 > > + /* state2[0,1,2,3] = state2[1,0,3,2] */ > > + pshufd $0x4e,state2,state2 > > + /* state3[0,1,2,3] = state3[2,1,0,3] */ > > + pshufd $0x93,state3,state3 > > The comments don't match the pshufd constants. The code is correct but the > comments are not. They should be:
Er, I swapped the endian when writing the comment. The code is fine though, yea. Fixed, thanks.
> The above sequence of 24 instructions is repeated twice, so maybe it should be a > macro (".chacha_round"?).
Not really a fan of the indirection when reading for something simple like this.
Thanks for the review.
Jason
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