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From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: Kairui Song <kasong@redhat.com>
Cc: linux-kernel@vger.kernel.org,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Matthew Garrett <matthewgarrett@google.com>,
	Baoquan He <bhe@redhat.com>, Dave Young <dyoung@redhat.com>,
	x86@kernel.org, linux-efi@vger.kernel.org
Subject: Re: [PATCH v2] x86, efi: never relocate kernel below lowest acceptable address
Date: Wed, 25 Sep 2019 12:51:14 +0300
Message-ID: <20190925095114.GB5173@linux.intel.com> (raw)
In-Reply-To: <20190919160521.13820-1-kasong@redhat.com>

On Fri, Sep 20, 2019 at 12:05:21AM +0800, Kairui Song wrote:
> Currently, kernel fails to boot on some HyperV VMs when using EFI.
> And it's a potential issue on all platforms.
> 
> It's caused a broken kernel relocation on EFI systems, when below three
> conditions are met:
> 
> 1. Kernel image is not loaded to the default address (LOAD_PHYSICAL_ADDR)
>    by the loader.
> 2. There isn't enough room to contain the kernel, starting from the
>    default load address (eg. something else occupied part the region).
> 3. In the memmap provided by EFI firmware, there is a memory region
>    starts below LOAD_PHYSICAL_ADDR, and suitable for containing the
>    kernel.
> 
> Efi stub will perform a kernel relocation when condition 1 is met. But
> due to condition 2, efi stub can't relocate kernel to the preferred
> address, so it fallback to query and alloc from EFI firmware for lowest
> usable memory region.
> 
> It's incorrect to use the lowest memory address. In later stage, kernel
> will assume LOAD_PHYSICAL_ADDR as the minimal acceptable relocate address,
> but efi stub will end up relocating kernel below it.
> 
> Then before the kernel decompressing. Kernel will do another relocation
> to address not lower than LOAD_PHYSICAL_ADDR, this time the relocate will
> over write the blockage at the default load address, which efi stub tried
> to avoid, and lead to unexpected behavior. Beside, the memory region it
> writes to is not allocated from EFI firmware, which is also wrong.
> 
> To fix it, just don't let efi stub relocate the kernel to any address
> lower than lowest acceptable address.
> 
> Signed-off-by: Kairui Song <kasong@redhat.com>

Acked-by:  <jarkko.sakkinen@linux.intel.com>

/Jarkko

  reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-19 16:05 Kairui Song
2019-09-25  9:51 ` Jarkko Sakkinen [this message]
2019-09-25 15:25 ` Ard Biesheuvel
2019-09-25 17:36   ` Kairui Song
2019-10-11 10:18     ` Kairui Song
2019-10-11 13:23 ` Borislav Petkov
2019-10-12  3:46   ` Kairui Song

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