Re: [PATCH] mm/vmalloc: widen guard region to defeat ENTER-based stack pivot

[Matthew Wilcox]

On Sun, Jun 28, 2026 at 07:09:37PM -0700, H. Peter Anvin wrote:
> On 2026-06-26 13:05, Xiang Mei wrote:
> > 
> > Thanks for your questions and attention.
> > 
> > 1) `enter` can do big enough stack pivoting (where we can't find many
> > `add/sub/adc/sbb rsp, ` doing so)
> 
> Say what?
> 
> Using add/sub/lea on %rsp is probably more common than enter, because enter is
> considered kind of slow.
> 
> gcc, I believe, will generate "leave" but not "enter" as a result.
> 
> 
> > 2) `enter` is not rare since we can take part in the instruction.
> 
> This sentence doesn't parse.

They mean that we can jump into the middle of an instruction, and it is
not rare to see a 'c8' byte in the instruction stream.