linux-kernel - Re: [PATCH v2] arm64, kaslr: export offset in VMCOREINFO ELF notes

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Message-ID: <303e32f7-ff47-ea9b-d5a0-45a22e44d0a9@arm.com>
Date:   Tue, 31 Jul 2018 10:19:35 +0100
From:   James Morse <james.morse@....com>
To:     Bhupesh Sharma <bhsharma@...hat.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org, bhupesh.linux@...il.com,
        takahiro.akashi@...aro.org, catalin.marinas@....com,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v2] arm64, kaslr: export offset in VMCOREINFO ELF notes

Hi Bhupesh,

On 30/07/18 07:24, Bhupesh Sharma wrote:
> Include KASLR offset in arm64 VMCOREINFO ELF notes to assist in
> debugging. vmcore parsing in user-space already expects this value in
> the notes and we are providing it for portability of those existing
> tools with x86.
> 
> Ideally we would like core code to do this (so that way this
> information won't be missed when an architecture adds KASLR support),
> but mips has CONFIG_RANDOMIZE_BASE, and doesn't provide kaslr_offset(),
> so I am not sure if this is needed for mips (and other such similar arch
> cases in future). So, lets keep this architecture specific for now.

(heh, I assumed you would rewrite my train-of-thought, but I guess this works!)


> As an example of a user-space use-case, consider the
> makedumpfile user-space utility which will need fixup to use this
> KASLR offset to work with cases where we need to find a way to
> translate symbol address from vmlinux to kernel run time address
> in case of KASLR boot on arm64.

Acked-by: James Morse <james.morse@....com>

If we want to send this to stable, it looks like it should have been part of the
KASLR series, f80fb3a3d5084 ("arm64: add support for kernel ASLR") was merged
for v4.6.
CC: <stable@...r.kernel.org> # 4.6.x


Thanks,

James


> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
> index f62effc6e064..028df356a5fd 100644
> --- a/arch/arm64/kernel/machine_kexec.c
> +++ b/arch/arm64/kernel/machine_kexec.c
> @@ -360,4 +360,5 @@ void arch_crash_save_vmcoreinfo(void)
>  						kimage_voffset);
>  	vmcoreinfo_append_str("NUMBER(PHYS_OFFSET)=0x%llx\n",
>  						PHYS_OFFSET);
> +	vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset());
>  }
>