linux-kernel - Re: [PATCH v3 4/5] x86/xen: Avoid relocatable quantities in Xen ELF notes

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Message-ID: <03b3647b-49f9-4a9a-be65-3170bde65730@amd.com>
Date: Wed, 9 Oct 2024 13:16:36 -0400
From: Jason Andryuk <jason.andryuk@....com>
To: Ard Biesheuvel <ardb+git@...gle.com>, <linux-kernel@...r.kernel.org>
CC: Ard Biesheuvel <ardb@...nel.org>, Juergen Gross <jgross@...e.com>, "Boris
 Ostrovsky" <boris.ostrovsky@...cle.com>, <x86@...nel.org>,
	<xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH v3 4/5] x86/xen: Avoid relocatable quantities in Xen ELF
 notes

On 2024-10-09 12:04, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
> 
> Xen puts virtual and physical addresses into ELF notes that are treated
> by the linker as relocatable by default. Doing so is not only pointless,
> given that the ELF notes are only intended for consumption by Xen before
> the kernel boots. It is also a KASLR leak, given that the kernel's ELF
> notes are exposed via the world readable /sys/kernel/notes.
> 
> So emit these constants in a way that prevents the linker from marking
> them as relocatable. This involves place-relative relocations (which
> subtract their own virtual address from the symbol value) and linker
> provided absolute symbols that add the address of the place to the
> desired value.
> 
> Tested-by: Jason Andryuk <jason.andryuk@....com>
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>

Reviewed-by: Jason Andryuk <jason.andryuk@....com>

Thanks,
Jason