From 0698fac4ac2ae84ecec2a826cc97803af564aa95 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Fri, 28 Feb 2020 13:14:06 +0100 Subject: [PATCH] efi/arm: Clean EFI stub exit code from cache instead of avoiding it The following commit: c7225494b ("efi/arm: Work around missing cache maintenance in decompressor handover") modified the EFI handover code written in assembler to work around the missing cache maintenance of the piece of code that is executed after the MMU and caches are turned off. Due to the fact that this sequence incorporates a subroutine call, cleaning that code from the cache is not a matter of simply passing the start and end of the currently running subroutine into cache_clean_flush(), which is why instead, the code jumps across into the cleaned copy of the 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 cache_clean_flush() call to cover the remaining code in the subroutine, and any code it may execute in the context of cache_off(). Signed-off-by: Ard Biesheuvel Signed-off-by: Ingo Molnar Cc: linux-efi@vger.kernel.org Cc: Ingo Molnar Cc: Thomas Gleixner Cc: David Hildenbrand Cc: Heinrich Schuchardt Cc: Tom Lendacky Link: https://lore.kernel.org/r/20200228121408.9075-5-ardb@kernel.org --- arch/arm/boot/compressed/head.S | 18 ++++++++---------- 1 file changed, 8 insertions(+), 10 deletions(-) diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S index 36ffbeecd30b..04f77214f050 100644 --- a/arch/arm/boot/compressed/head.S +++ b/arch/arm/boot/compressed/head.S @@ -1452,13 +1452,11 @@ ENTRY(efi_enter_kernel) @ The PE/COFF loader might not have cleaned the code we are @ running beyond the PoU, and so calling cache_off below from - @ inside the PE/COFF loader allocated region is unsafe. Let's - @ assume our own zImage relocation code did a better job, and - @ jump into its version of this routine before proceeding. - ldr r1, .Ljmp - sub r1, r7, r1 - mov pc, r1 @ no mode switch -0: + @ inside the PE/COFF loader allocated region is unsafe unless + @ we explicitly clean it to the PoC. + adr r0, call_cache_fn @ region of code we will + adr r1, 0f @ run with MMU off + bl cache_clean_flush bl cache_off @ Set parameters for booting zImage according to boot protocol @@ -1467,10 +1465,10 @@ ENTRY(efi_enter_kernel) mov r0, #0 mov r1, #0xFFFFFFFF mov r2, r4 - b __efi_start + add r7, r7, #(__efi_start - start) + mov pc, r7 @ no mode switch ENDPROC(efi_enter_kernel) - .align 2 -.Ljmp: .long start - 0b +0: #endif .align -- 2.34.1