efi/libstub/arm: Make efi_entry() an ordinary PE/COFF entrypoint

Expose efi_entry() as the PE/COFF entrypoint directly, instead of
jumping into a wrapper that fiddles with stack buffers and other
stuff that the compiler is much better at. The only reason this
code exists is to obtain a pointer to the base of the image, but
we can get the same value from the loaded_image protocol, which
we already need for other reasons anyway.

Update the return type as well, to make it consistent with what
is required for a PE/COFF executable entrypoint.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

5 files changed, 31 insertions, 105 deletions

diff --git a/arch/arm/boot/compressed/efi-header.S b/arch/arm/boot/compressed/efi-header.S
index a5983588f96b..e38fbda02b93 100644
--- a/arch/arm/boot/compressed/efi-header.S
+++ b/arch/arm/boot/compressed/efi-header.S
@@ -60,7 +60,7 @@ optional_header:
 		.long	__pecoff_code_size		@ SizeOfCode
 		.long	__pecoff_data_size		@ SizeOfInitializedData
 		.long	0				@ SizeOfUninitializedData
-		.long	efi_stub_entry - start		@ AddressOfEntryPoint
+		.long	efi_entry - start		@ AddressOfEntryPoint
 		.long	start_offset			@ BaseOfCode
 		.long	__pecoff_data_start - start	@ BaseOfData
 
diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index 8487221bedb0..36ffbeecd30b 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -1437,33 +1437,15 @@ __enter_kernel:
 reloc_code_end:
 
 #ifdef CONFIG_EFI_STUB
-		.align	2
-_start:		.long	start - .
-
-ENTRY(efi_stub_entry)
-		@ allocate space on stack for passing current zImage address
-		@ and for the EFI stub to return of new entry point of
-		@ zImage, as EFI stub may copy the kernel. Pointer address
-		@ is passed in r2. r0 and r1 are passed through from the
-		@ EFI firmware to efi_entry
-		adr	ip, _start
-		ldr	r3, [ip]
-		add	r3, r3, ip
-		stmfd	sp!, {r3, lr}
-		mov	r2, sp			@ pass zImage address in r2
-		bl	efi_entry
-
-		@ Check for error return from EFI stub. r0 has FDT address
-		@ or error code.
-		cmn	r0, #1
-		beq	efi_load_fail
-
-		@ Preserve return value of efi_entry() in r4
-		mov	r4, r0
-		add	r1, r4, #SZ_2M			@ DT end
+ENTRY(efi_enter_kernel)
+		mov	r7, r0				@ preserve image base
+		mov	r4, r1				@ preserve DT pointer
+
+		mov	r0, r4				@ DT start
+		add	r1, r4, r2			@ DT end
 		bl	cache_clean_flush
 
-		ldr	r0, [sp]			@ relocated zImage
+		mov	r0, r7				@ relocated zImage
 		ldr	r1, =_edata			@ size of zImage
 		add	r1, r1, r0			@ end of zImage
 		bl	cache_clean_flush
@@ -1473,9 +1455,8 @@ ENTRY(efi_stub_entry)
 		@ 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	r0, [sp]			@ relocated zImage
 		ldr	r1, .Ljmp
-		sub	r1, r0, r1
+		sub	r1, r7, r1
 		mov	pc, r1				@ no mode switch
 0:
 		bl	cache_off
@@ -1487,12 +1468,7 @@ ENTRY(efi_stub_entry)
 		mov	r1, #0xFFFFFFFF
 		mov	r2, r4
 		b	__efi_start
-
-efi_load_fail:
-		@ Return EFI_LOAD_ERROR to EFI firmware on error.
-		ldr	r0, =0x80000001
-		ldmfd	sp!, {ip, pc}
-ENDPROC(efi_stub_entry)
+ENDPROC(efi_enter_kernel)
 		.align	2
 .Ljmp:		.long	start - 0b
 #endif
diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S
index 304d5b02ca67..4cfd03c35c49 100644
--- a/arch/arm64/kernel/efi-entry.S
+++ b/arch/arm64/kernel/efi-entry.S
@@ -10,81 +10,35 @@
 
 #include <asm/assembler.h>
 
-#define EFI_LOAD_ERROR 0x8000000000000001
-
 	__INIT
 
-	/*
-	 * We arrive here from the EFI boot manager with:
-	 *
-	 *    * CPU in little-endian mode
-	 *    * MMU on with identity-mapped RAM
-	 *    * Icache and Dcache on
-	 *
-	 * We will most likely be running from some place other than where
-	 * we want to be. The kernel image wants to be placed at TEXT_OFFSET
-	 * from start of RAM.
-	 */
-ENTRY(entry)
-	/*
-	 * Create a stack frame to save FP/LR with extra space
-	 * for image_addr variable passed to efi_entry().
-	 */
-	stp	x29, x30, [sp, #-32]!
-	mov	x29, sp
-
-	/*
-	 * Call efi_entry to do the real work.
-	 * x0 and x1 are already set up by firmware. Current runtime
-	 * address of image is calculated and passed via *image_addr.
-	 *
-	 * unsigned long efi_entry(void *handle,
-	 *                         efi_system_table_t *sys_table,
-	 *                         unsigned long *image_addr) ;
-	 */
-	adr_l	x8, _text
-	add	x2, sp, 16
-	str	x8, [x2]
-	bl	efi_entry
-	cmn	x0, #1
-	b.eq	efi_load_fail
-
+ENTRY(efi_enter_kernel)
 	/*
 	 * efi_entry() will have copied the kernel image if necessary and we
-	 * return here with device tree address in x0 and the kernel entry
-	 * point stored at *image_addr. Save those values in registers which
-	 * are callee preserved.
-	 */
-	mov	x20, x0		// DTB address
-	ldr	x0, [sp, #16]	// relocated _text address
-	ldr	w21, =stext_offset
-	add	x21, x0, x21
-
-	/*
-	 * Calculate size of the kernel Image (same for original and copy).
+	 * 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.
 	 */
-	adr_l	x1, _text
-	adr_l	x2, _edata
-	sub	x1, x2, x1
+	mov	x19, x0			// relocated Image address
+	mov	x20, x1			// DTB address
 
 	/*
 	 * Flush 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
 	ic	ialluis
+	dsb	sy
 
 	/*
-	 * Ensure that the rest of this function (in the original Image) is
-	 * visible when the caches are disabled. The I-cache can't have stale
-	 * entries for the VA range of the current image, so no maintenance is
-	 * necessary.
+	 * 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.
 	 */
-	adr	x0, entry
-	adr	x1, entry_end
-	sub	x1, x1, x0
-	bl	__flush_dcache_area
-
+	ldr	w0, .Ljmp
+	sub	x0, x19, w0, sxtw
+	br	x0
+0:
 	/* Turn off Dcache and MMU */
 	mrs	x0, CurrentEL
 	cmp	x0, #CurrentEL_EL2
@@ -109,12 +63,6 @@ ENTRY(entry)
 	mov	x1, xzr
 	mov	x2, xzr
 	mov	x3, xzr
-	br	x21
-
-efi_load_fail:
-	mov	x0, #EFI_LOAD_ERROR
-	ldp	x29, x30, [sp], #32
-	ret
-
-entry_end:
-ENDPROC(entry)
+	b	stext
+ENDPROC(efi_enter_kernel)
+.Ljmp:	.long	_text - 0b
diff --git a/arch/arm64/kernel/efi-header.S b/arch/arm64/kernel/efi-header.S
index a7cfacce3e15..40c704c5d3a5 100644
--- a/arch/arm64/kernel/efi-header.S
+++ b/arch/arm64/kernel/efi-header.S
@@ -27,7 +27,7 @@ optional_header:
 	.long	__initdata_begin - efi_header_end	// SizeOfCode
 	.long	__pecoff_data_size			// SizeOfInitializedData
 	.long	0					// SizeOfUninitializedData
-	.long	__efistub_entry - _head			// AddressOfEntryPoint
+	.long	__efistub_efi_entry - _head		// AddressOfEntryPoint
 	.long	efi_header_end - _head			// BaseOfCode
 
 extra_header_fields:
diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
index 25a2a9b479c2..87cb3d45b4bd 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -12,7 +12,8 @@
 
 #ifdef CONFIG_EFI
 
-__efistub_stext_offset = stext - _text;
+__efistub_kernel_size		= _edata - _text;
+
 
 /*
  * The EFI stub has its own symbol namespace prefixed by __efistub_, to
@@ -42,6 +43,7 @@ __efistub___memset		= __pi_memset;
 #endif
 
 __efistub__text			= _text;
+__efistub_stext			= stext;
 __efistub__end			= _end;
 __efistub__edata		= _edata;
 __efistub_screen_info		= screen_info;