Commit b9676962 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Ingo Molnar
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efi/arm64: Clean EFI stub exit code from cache instead of avoiding it 



Commit 9f922377 ("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 __clean_dcache_area_poc() call to cover
the remaining code in the subroutine. While at it, switch the other
call site over to __clean_dcache_area_poc() as well, and clean up the
terminology in comments to avoid using 'flush' in the context of cache
maintenance. Also, let's switch to the new style asm annotations.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: linux-efi@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20200228121408.9075-6-ardb@kernel.org
parent 0698fac4

arch/arm64/kernel/efi-entry.S

+13 −13
Original line number Diff line number Diff line
@@ -12,32 +12,32 @@ 


	__INIT



ENTRY(efi_enter_kernel)

SYM_CODE_START(efi_enter_kernel)

	/*

	 * efi_entry() will have copied the kernel image if necessary and we

	 * end up here with device tree address in x1 and the kernel entry

	 * 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



	/*

	 * Flush the copied Image to the PoC, and ensure it is not shadowed by

	 * Clean the copied Image to the PoC, and ensure it is not shadowed by

	 * stale icache entries from before relocation.

	 */

	ldr	w1, =kernel_size

	bl	__flush_dcache_area

	bl	__clean_dcache_area_poc

	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.

	 * Clean the remainder of this routine to the PoC

	 * 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	__clean_dcache_area_poc

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

ENDPROC(efi_enter_kernel)

.Ljmp:	.long	_text - 0b
 
	br	x19

SYM_CODE_END(efi_enter_kernel)

3:	.long	. - 0b

arch/arm64/kernel/image-vars.h

+2 −2
Original line number Diff line number Diff line
@@ -13,6 +13,7 @@ 
#ifdef CONFIG_EFI



__efistub_kernel_size		= _edata - _text;

__efistub_stext_offset		= stext - _text;





/*
@@ -34,7 +35,7 @@ __efistub_strnlen = __pi_strnlen; 
__efistub_strcmp		= __pi_strcmp;

__efistub_strncmp		= __pi_strncmp;

__efistub_strrchr		= __pi_strrchr;

__efistub___flush_dcache_area	= __pi___flush_dcache_area;

__efistub___clean_dcache_area_poc = __pi___clean_dcache_area_poc;



#ifdef CONFIG_KASAN

__efistub___memcpy		= __pi_memcpy;
@@ -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;

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