Re: [PATCH 3/6] x86/entry_32: Add VERW just before userspace transition

Andi Kleen
2023-10-20T23:49:57Z

On Fri, Oct 20, 2023 at 01:45:09PM -0700, Pawan Gupta wrote:
> As done for entry_64, add support for executing VERW late in exit to
> user path for 32-bit mode.
>
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> ---
> arch/x86/entry/entry_32.S | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
> index 6e6af42e044a..bbf77d2aab2e 100644
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -886,6 +886,9 @@ SYM_FUNC_START(entry_SYSENTER_32)
> popfl
> popl %eax
>
> + /* Mitigate CPU data sampling attacks .e.g. MDS */
> + USER_CLEAR_CPU_BUFFERS
> +
> /*
> * Return back to the vDSO, which will pop ecx and edx.
> * Don't bother with DS and ES (they already contain __USER_DS).

Did you forget the INT 0x80 entry point?

-Andi