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.
Thanks,
Mark.
> + * so that we can safely disable the MMU and caches.
> */
> - ldr w0, .Ljmp
> - sub x0, x19, w0, sxtw
> - br x0
> + adr x0, 0f
> + ldr w1, 3f
> + bl __flush_dcache_area
> 0:
> /* Turn off Dcache and MMU */
> mrs x0, CurrentEL
> @@ -63,6 +63,6 @@ ENTRY(efi_enter_kernel)
> mov x1, xzr
> mov x2, xzr
> mov x3, xzr
> - b stext
> + br x19
> ENDPROC(efi_enter_kernel)
> -.Ljmp: .long _text - 0b
> +3: .long . - 0b
> diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
> index 9a7aef0d6f70..28bf98f84adf 100644
> --- a/arch/arm64/kernel/image-vars.h
> +++ b/arch/arm64/kernel/image-vars.h
> @@ -13,6 +13,7 @@
> #ifdef CONFIG_EFI
>
> __efistub_kernel_size = _edata - _text;
> +__efistub_stext_offset = stext - _text;
>
>
> /*
> @@ -43,7 +44,6 @@ __efistub___memset = __pi_memset;
> #endif
>
> __efistub__text = _text;
> -__efistub_stext = stext;
> __efistub__end = _end;
> __efistub__edata = _edata;
> __efistub_screen_info = screen_info;
> --
> 2.17.1
>
