linux-kernel - Re: [PATCH v3 02/60] arm64: mm: Take potential load offset into account when KASLR is off

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Message-ID: <ZEuiyaINUp+bXgx2@FVFF77S0Q05N>
Date:   Fri, 28 Apr 2023 11:41:13 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Ryan Roberts <ryan.roberts@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v3 02/60] arm64: mm: Take potential load offset into
 account when KASLR is off

On Tue, Mar 07, 2023 at 03:04:24PM +0100, Ard Biesheuvel wrote:
> We enable CONFIG_RELOCATABLE even when CONFIG_RANDOMIZE_BASE is
> disabled, and this permits the loader (i.e., EFI) to place the kernel
> anywhere in physical memory as long as the base address is 64k aligned.
> 
> This means that the 'KASLR' case described in the header that defines
> the size of the statically allocated page tables could take effect even
> when CONFIG_RANDMIZE_BASE=n. So check for CONFIG_RELOCATABLE instead.

Could we pleqase update the comment to describe that? As of this commit it'll
be left describing a KASLR-specific case, and it'd be good to have it mention
the case described in this commit message.

Thanks,
Mark.

> 
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
> ---
>  arch/arm64/include/asm/kernel-pgtable.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
> index fcd14197756f0619..4d13c73171e1e360 100644
> --- a/arch/arm64/include/asm/kernel-pgtable.h
> +++ b/arch/arm64/include/asm/kernel-pgtable.h
> @@ -53,7 +53,7 @@
>   * address is just pushed over a boundary and the start address isn't).
>   */
>  
> -#ifdef CONFIG_RANDOMIZE_BASE
> +#ifdef CONFIG_RELOCATABLE
>  #define EARLY_KASLR	(1)
>  #else
>  #define EARLY_KASLR	(0)
> -- 
> 2.39.2
> 
>