linux-kernel - Re: [PATCH] random: vDSO: assume key is 32-bit aligned on x86

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAHmME9qMCsAfqRR+p5CYj878R0EBGp+RbV8K=fz3XNfsK2gFXQ@mail.gmail.com>
Date: Wed, 28 Aug 2024 19:09:24 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org, 
	christophe.leroy@...roup.eu
Subject: Re: [PATCH] random: vDSO: assume key is 32-bit aligned on x86_64

On Wed, Aug 28, 2024 at 7:03 PM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> The prototype of this function ensures a u32* type for the key, and all
> uses of it are using state->key, which is a u32 array. When userspace
> slices up a memory region into an array of states, it does so using a
> state size that also ensures the alignment. So it's safe to assume that
> the key is always 32-bit aligned. That in turn means it's possible to
> use movaps instead of movups for loading the key.
>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
>  arch/x86/entry/vdso/vgetrandom-chacha.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/entry/vdso/vgetrandom-chacha.S b/arch/x86/entry/vdso/vgetrandom-chacha.S
> index bcba5639b8ee..07ae91dcdbda 100644
> --- a/arch/x86/entry/vdso/vgetrandom-chacha.S
> +++ b/arch/x86/entry/vdso/vgetrandom-chacha.S
> @@ -43,8 +43,8 @@ SYM_FUNC_START(__arch_chacha20_blocks_nostack)
>         /* copy0 = "expand 32-byte k" */
>         movaps          CONSTANTS(%rip),copy0
>         /* copy1,copy2 = key */
> -       movups          0x00(key),copy1
> -       movups          0x10(key),copy2
> +       movaps          0x00(key),copy1
> +       movaps          0x10(key),copy2

Zomg, no coffee today. movaps requires 128-bit alignment! So this
won't do. Forget you ever saw this.