| Message ID | 20240828170350.3422587-1-Jason@zx2c4.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Herbert Xu |
| Headers | show |
| Series | random: vDSO: assume key is 32-bit aligned on x86_64 | expand |
On Wed, Aug 28, 2024 at 7:03 PM Jason A. Donenfeld <Jason@zx2c4.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@zx2c4.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.
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 /* copy3 = counter || zero nonce */ movq 0x00(counter),copy3 /* one = 1 || 0 */
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@zx2c4.com> --- arch/x86/entry/vdso/vgetrandom-chacha.S | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)