linux-kernel - Re: [RFC PATCH] x86/Kconfig: Disable KASLR on debug builds

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Message-ID: <20231130181051.GA3357088@dev-arch.thelio-3990X>
Date:   Thu, 30 Nov 2023 11:10:51 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] x86/Kconfig: Disable KASLR on debug builds

On Thu, Nov 30, 2023 at 01:05:52PM +0100, Borislav Petkov wrote:
> From: "Borislav Petkov (AMD)" <bp@...en8.de>
> 
> Having KASLR enabled makes debugging a kernel completely useless because
> virtual addresses are not stable, leading to people poking at kernel
> internals to have to go and rebuild with RANDOMIZE_BASE=off.
> 
> Just disable it on debugging builds where it is not needed anyway.
> 
> Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>

I know Peter pointed out that there is a runtime switch for this, which
should make this patch obsolete but in case there is more reasons needed
for why this might be a bad idea, most distribution configurations have
CONFIG_DEBUG_KERNEL enabled because CONFIG_EXPERT selects it:

archlinux/x86_64.config:CONFIG_DEBUG_KERNEL=y
debian/amd64.config:CONFIG_DEBUG_KERNEL=y
fedora/x86_64.config:CONFIG_DEBUG_KERNEL=y
opensuse/x86_64.config:CONFIG_DEBUG_KERNEL=y

> ---
>  arch/x86/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index c456c9b1fc7c..da94354b1b75 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -2159,7 +2159,7 @@ config RELOCATABLE
>  
>  config RANDOMIZE_BASE
>  	bool "Randomize the address of the kernel image (KASLR)"
> -	depends on RELOCATABLE
> +	depends on RELOCATABLE && !DEBUG_KERNEL
>  	default y
>  	help
>  	  In support of Kernel Address Space Layout Randomization (KASLR),
> -- 
> 2.42.0.rc0.25.ga82fb66fed25
>