linux-kernel - Re: [PATCH] x86/mm, efi: Check for valid image type

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Date:	Wed, 29 Jul 2015 17:37:52 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	josh@...htriplett.org, Matt Fleming <matt@...eblueprint.co.uk>,
	Matt Fleming <matt.fleming@...el.com>, x86@...nel.org,
	linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/mm, efi: Check for valid image type

Hi,

> 
> >  As you pointed out above, a wild pointer could cause a
> > WARN from early_ioremap.  We need to never follow the pointer in the
> > first place after a kexec, unless we have some way to know that it's
> > actually valid.
> 
> So you assume that the information from ACPI is always correct then?
> The pointer is correct, the information it points to is no longer.
> 
> If we run always under EFI then it looks like the variable efi_setup
> which is checked in efi_enter_virtual_mode() is 0 during normal boot
> and != 0 on kexec entry. This hint is set via setup_data / SETUP_EFI
> since commit 1fec053369 ("x86/efi: Pass necessary EFI data for kexec
> via setup_data"). So maybe we could use this to check if we run under
> kexec or not.

Not sure if BGRT is useful in kexec kernel, it seems not worth to copy
it between kernels.

IMO just return in case if (efi_setup) is true make sense.

Thanks
Dave
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