[PATCH 5/8] efi: Get the secure boot status [ver #6]
matt at codeblueprint.co.uk
Mon Jan 16 06:49:54 PST 2017
(Cc'ing Peter A. and Peter J. for boot params discussion)
On Wed, 11 Jan, at 03:27:23PM, David Howells wrote:
> Matt Fleming <matt at codeblueprint.co.uk> wrote:
> > > + movb $0, BP_secure_boot(%rsi)
> > > #ifdef CONFIG_EFI_STUB
> > > /*
> > > * The entry point for the PE/COFF executable is efi_pe_entry, so
> > Is clearing ::secure_boot really necessary? Any code path that goes
> > via efi_main() will set it correctly and all other code paths should
> > get it cleared in sanitize_boot_params(), no?
> The boot_params->secure_boot parameter exists whether or not efi_main() is
> traversed (ie. if EFI isn't enabled or CONFIG_EFI_STUB=n) and, if not cleared,
> is of uncertain value.
> Further, sanitize_boot_params() has to be modified by this patch so as not to
> clobber the secure_boot flag.
Any new parameters that boot loaders do not know about should be
cleared to zero by default in the boot loader because boot_params
itself should be zero'd when allocated.
There are two cases to consider:
1) boot_params is not zero'd
2) boot_params is zero'd
1) This is a broken boot loader implementation that violates the x86
boot specification and I would never expect ->secure_boot to have a
valid value. It should not be special-cased in sanitize_boot_params(),
it should be zero'd.
2) In this case ->secure_boot should be zero unless modified inside of
Did you hit the scenario where ->secure_boot has a garbage value while
developing these patches? I wouldn't expect to see it in practice.
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