Re: [PATCH v2 05/20] x86: decompressor: Avoid the need for a stack in the 32-bit trampoline

[Kirill A. Shutemov]

On Mon, May 08, 2023 at 09:03:15AM +0200, Ard Biesheuvel wrote:
> The 32-bit trampoline no longer uses the stack for anything except
> performing a long return back to long mode. Currently, this stack is
> allocated in the same page that carries the trampoline code, which means
> this page must be mapped writable and executable, and the stack is
> therefore executable as well.
> 
> So let's do a long jump instead: that way, we can pre-calculate the
> return address and poke it into the code before we call it. In a later
> patch, we will take advantage of this by removing writable permissions
> (and adding executable ones) explicitly when booting via the EFI stub.
> 
> Not playing with the stack pointer also makes it more straight-forward
> to call the trampoline code as an ordinary 64-bit function from C code.
> 
> Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>

Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov