linux-kernel - Re: [PATCH 1/1] x86/boot/compressed: Fix avoiding memmap in physical KASLR

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Message-ID: <CAMj1kXErKwmiM5AiGOCE5D39U+3o_MXz5vqJmE5pkjQV308d9w@mail.gmail.com>
Date: Sat, 21 Jun 2025 10:18:49 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Michal Clapinski <mclapinski@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Dan Williams <dan.j.williams@...el.com>, 
	Pasha Tatashin <pasha.tatashin@...een.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] x86/boot/compressed: Fix avoiding memmap in physical KASLR

Hi Michal,

On Tue, 10 Jun 2025 at 23:42, Michal Clapinski <mclapinski@...gle.com> wrote:
>
> The intent of the code was to cancel KASLR if there are more than 4
> memmap args. Unfortunately, it was only doing that if the memmap args
> were comma delimited, not if they were entirely separate.
> This change fixes it.
>
> Signed-off-by: Michal Clapinski <mclapinski@...gle.com>
> ---
> I would like KASLR to support more than 4 memmap args. Do you think
> I can just increase the MAX_MEMMAP_REGIONS or should I implement
> support for the general case?
>
>  arch/x86/boot/compressed/kaslr.c | 3 ---
>  1 file changed, 3 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index f03d59ea6e40..4aa9c9781ca7 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -162,9 +162,6 @@ static void mem_avoid_memmap(char *str)
>  {
>         static int i;
>
> -       if (i >= MAX_MEMMAP_REGIONS)
> -               return;
> -

It isn't obvious at all why simply dropping this condition is fine.
Could you elaborate?

>         while (str && (i < MAX_MEMMAP_REGIONS)) {
>                 int rc;
>                 u64 start, size;
> --
> 2.50.0.rc0.642.g800a2b2222-goog
>