On Fri, Feb 28, 2020 at 11:14:50AM +0000, Mark Rutland wrote:
> On Fri, Feb 28, 2020 at 11:02:43AM +0100, Ard Biesheuvel wrote:
> > Commit 9f9223778 ("efi/libstub/arm: Make efi_entry() an ordinary PE/COFF
> > entrypoint") modified the handover code written in assembler, and for
> > maintainability, aligned the logic with the logic used in the 32-bit ARM
> > version, which is to avoid cache maintenance on the remaining instructions
> > in the subroutine that will be executed with the MMU and caches off, and
> > instead, branch into the relocated copy of the kernel image.
> >
> > However, this assumes that this copy is executable, and this means we
> > expect EFI_LOADER_DATA regions to be executable as well, which is not
> > a reasonable assumption to make, even if this is true for most UEFI
> > implementations today.
> >
> > So change this back, and add a __flush_dcache_area() call to cover the
> > remaining code in the subroutine.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> > ---
> > arch/arm64/kernel/efi-entry.S | 18 +++++++++---------
> > arch/arm64/kernel/image-vars.h | 2 +-
> > 2 files changed, 10 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S
> > index 4cfd03c35c49..d5dee064975f 100644
> > --- a/arch/arm64/kernel/efi-entry.S
> > +++ b/arch/arm64/kernel/efi-entry.S
> > @@ -19,7 +19,8 @@ ENTRY(efi_enter_kernel)
> > * point stored in x0. Save those values in registers which are
> > * callee preserved.
> > */
> > - mov x19, x0 // relocated Image address
> > + ldr w2, =stext_offset
> > + add x19, x0, x2 // relocated Image entrypoint
> > mov x20, x1 // DTB address
> >
> > /*
> > @@ -29,15 +30,14 @@ ENTRY(efi_enter_kernel)
> > ldr w1, =kernel_size
> > bl __flush_dcache_area
> > ic ialluis
> > - dsb sy
> >
> > /*
> > - * Jump across, into the copy of the image that we just cleaned
> > - * to the PoC, so that we can safely disable the MMU and caches.
> > + * Flush the remainder of this routine to the PoC
>
> Minor nit, but could we please say 'Clean' rather than 'Flush' here?
>
> Even better, we now have __clean_dcache_area_poc(), and can use that
> too.
... or if that's better as a subsequent cleanup for consistency, that'd
also be fine, and needn't block this patch.
Thanks,
Mark.
