Re: [PATCH] x86/boot: efistub: Assign global boot_params variable

[Ingo Molnar <mingo@kernel.org>]

* Ard Biesheuvel <ardb@kernel.org> wrote:

> On Tue, 17 Oct 2023 at 13:34, Ingo Molnar <mingo@kernel.org> wrote:
> >
> >
> > * Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > > On Mon, 16 Oct 2023 at 18:46, Ard Biesheuvel <ardb@google.com> wrote:
> > > >
> > > > From: Ard Biesheuvel <ardb@kernel.org>
> > > >
> > > > Now that the x86 EFI stub calls into some APIs exposed by the
> > > > decompressor (e.g., kaslr_get_random_long()), it is necessary to ensure
> > > > that the global boot_params variable is set correctly before doing so.
> > > >
> > > > Note that the decompressor and the kernel proper carry conflicting
> > > > declarations for the global variable 'boot_params' so refer to it via an
> > > > alias to work around this.
> > > >
> > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > > > ---
> > > >  drivers/firmware/efi/libstub/x86-stub.c | 3 +++
> > > >  1 file changed, 3 insertions(+)
> > > >
> > > > diff --git a/drivers/firmware/efi/libstub/x86-stub.c b/drivers/firmware/efi/libstub/x86-stub.c
> > > > index 3bfc59637dd1..51407207ded5 100644
> > > > --- a/drivers/firmware/efi/libstub/x86-stub.c
> > > > +++ b/drivers/firmware/efi/libstub/x86-stub.c
> > > > @@ -812,12 +812,15 @@ void __noreturn efi_stub_entry(efi_handle_t handle,
> > > >                                efi_system_table_t *sys_table_arg,
> > > >                                struct boot_params *boot_params)
> > > >  {
> > > > +       extern struct boot_params *bpp asm("boot_params");
> > >
> > > I am getting hatemail from the bots about this extern declaration, so
> > > I will move that into x86-stub.h.
> >
> > Hm, it would be better if we moved all of x86-stub.h into
> > arch/x86/include/asm/ or so. We don't really encourage "deep" driver-level
> > exports like that, and there's little reason why this couldn't be in the
> > x86 headers, right?
> >
> 
> Yes, there is.
> 
> arch/x86/boot/compressed/misc.h:extern struct boot_params *boot_params;
> arch/x86/include/asm/setup.h:extern struct boot_params boot_params;
> 
> Ideally, we should get rid of the first one.
> 
> Happy to send a patch that replaces all conflicting uses in the
> decompressor, so we can just access the global pointer without these
> tricks.

Yeah, that would be lovely, thanks.

> But I'd like to get the fix in for v6.6 in any case.

Sure:

  Acked-by: Ingo Molnar <mingo@kernel.org>

Thanks,

	Ingo