On 10/28/2024 9:07 AM, Alexander Shishkin wrote:
> Since EMULATE mode of vsyscall disables LASS, because fixing the LASS
> violations during the EMULATE mode would need complex instruction
> decoding, document this fact in kernel-parameters.txt.
>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Suggested-by: Dave Hansen <dave.hansen@xxxxxxxxx>
> Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
It might be better to combine this patch with the previous one. Both the
patches are small enough and related to the same thing.
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 1518343bbe22..4091dc48670a 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -7391,7 +7391,9 @@
>
> emulate Vsyscalls turn into traps and are emulated
> reasonably safely. The vsyscall page is
> - readable.
> + readable. This also disables the LASS
> + feature to allow userspace to poke around
> + the vsyscall page.
>
I am not sure if the person reading this guide would be aware of LASS.
Also the way the sentence is structured it might be easy to misinterpret
its meaning.
How about something like:
emulate Vsyscalls turn into traps and are emulated
reasonably safely. The vsyscall page is
readable. This disables the linear
address space separation (LASS) security
feature and makes the system less secure.
> xonly [default] Vsyscalls turn into traps and are
> emulated reasonably safely. The vsyscall
