Subject: [PATCH] efi/libstub/arm: make efi_entry() an ordinary PE/COFF entrypoint

From: Ard Biesheuvel <[email-masked]>
Date: Mon, 17 Feb 2020 13:49:04 +0100

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 <[email-masked]>
---
Apologies to Atish for making him track a moving target, but this is another
bit of cleanup work that I would like to merge before taking the RISC-V
changes on top.

On RISC-V, I would expect efi_enter_kernel() to be implemented as a C routine
that finds the hart id in the DT (which is passed as an argument), and pass
it to the startup code of the kernel proper.

 arch/arm/boot/compressed/efi-header.S     |  2 +-
 arch/arm/boot/compressed/head.S           | 44 +++-----------
 arch/arm64/kernel/efi-entry.S             | 64 +++-----------------
 arch/arm64/kernel/efi-header.S            |  2 +-
 drivers/firmware/efi/libstub/arm-stub.c   | 37 +++++------
 drivers/firmware/efi/libstub/arm32-stub.c |  1 +
 drivers/firmware/efi/libstub/arm64-stub.c |  3 +-
 7 files changed, 42 insertions(+), 111 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 088b0a060876..941cd28a13c3 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -1437,50 +1437,22 @@ __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
+ENTRY(efi_enter_kernel)
+		mov	r4, r0			@ preserve entrypoint
+		mov	r5, r1			@ preserve DT pointer
 		bl	cache_clean_flush
 		bl	cache_off
 
 		@ Set parameters for booting zImage according to boot protocol
-		@ put FDT address in r2, it was returned by efi_entry()
-		@ r1 is the machine type, and r0 needs to be 0
 		mov	r0, #0
 		mov	r1, #0xFFFFFFFF
-		mov	r2, r4
+		mov	r2, r5
 
-		@ Branch to (possibly) relocated zImage that is in [sp]
-		ldr	lr, [sp]
+		@ Branch to (possibly) relocated zImage @ [r4]
 		ldr	ip, =start_offset
-		add	lr, lr, ip
-		mov	pc, lr				@ no mode switch
-
-efi_load_fail:
-		@ Return EFI_LOAD_ERROR to EFI firmware on error.
-		ldr	r0, =0x80000001
-		ldmfd	sp!, {ip, pc}
-ENDPROC(efi_stub_entry)
+		add	r4, r4, ip
+		mov	pc, r4			@ no mode switch
+ENDPROC(efi_enter_kernel)
 #endif
 
 		.align
diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S
index 304d5b02ca67..49e3b1ad1b36 100644
--- a/arch/arm64/kernel/efi-entry.S
+++ b/arch/arm64/kernel/efi-entry.S
@@ -10,55 +10,18 @@
 
 #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.
+	 * 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	x20, x0		// DTB address
-	ldr	x0, [sp, #16]	// relocated _text address
+	mov	x20, x1			// DTB address
 	ldr	w21, =stext_offset
-	add	x21, x0, x21
+	add	x21, x0, x21		// relocated Image address
 
 	/*
 	 * Calculate size of the kernel Image (same for original and copy).
@@ -80,9 +43,8 @@ ENTRY(entry)
 	 * entries for the VA range of the current image, so no maintenance is
 	 * necessary.
 	 */
-	adr	x0, entry
-	adr	x1, entry_end
-	sub	x1, x1, x0
+	adr	x0, efi_enter_kernel
+	mov	x1, efi_enter_kernel_size
 	bl	__flush_dcache_area
 
 	/* Turn off Dcache and MMU */
@@ -110,11 +72,5 @@ ENTRY(entry)
 	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)
+ENDPROC(efi_enter_kernel)
+	.set	efi_enter_kernel_size, . - efi_enter_kernel
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/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
index 56e475c1aa55..439c094f7bf2 100644
--- a/drivers/firmware/efi/libstub/arm-stub.c
+++ b/drivers/firmware/efi/libstub/arm-stub.c
@@ -133,17 +133,20 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
 				 unsigned long *reserve_size,
 				 unsigned long dram_base,
 				 efi_loaded_image_t *image);
+
+void __noreturn efi_enter_kernel(unsigned long entrypoint, unsigned long fdt);
+
 /*
  * EFI entry point for the arm/arm64 EFI stubs.  This is the entrypoint
  * that is described in the PE/COFF header.  Most of the code is the same
  * for both archictectures, with the arch-specific code provided in the
  * handle_kernel_image() function.
  */
-unsigned long efi_entry(void *handle, efi_system_table_t *sys_table_arg,
-			       unsigned long *image_addr)
+efi_status_t efi_entry(efi_handle_t handle, efi_system_table_t *sys_table_arg)
 {
 	efi_loaded_image_t *image;
 	efi_status_t status;
+	unsigned long image_addr;
 	unsigned long image_size = 0;
 	unsigned long dram_base;
 	/* addr/point and size pairs for memory management*/
@@ -153,7 +156,6 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table_arg,
 	unsigned long fdt_size = 0;
 	char *cmdline_ptr = NULL;
 	int cmdline_size = 0;
-	unsigned long new_fdt_addr;
 	efi_guid_t loaded_image_proto = LOADED_IMAGE_PROTOCOL_GUID;
 	unsigned long reserve_addr = 0;
 	unsigned long reserve_size = 0;
@@ -165,8 +167,10 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table_arg,
 	sys_table = sys_table_arg;
 
 	/* Check if we were booted by the EFI firmware */
-	if (sys_table->hdr.signature != EFI_SYSTEM_TABLE_SIGNATURE)
+	if (sys_table->hdr.signature != EFI_SYSTEM_TABLE_SIGNATURE) {
+		status = EFI_INVALID_PARAMETER;
 		goto fail;
+	}
 
 	status = check_platform_features();
 	if (status != EFI_SUCCESS)
@@ -187,6 +191,7 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table_arg,
 	dram_base = get_dram_base();
 	if (dram_base == EFI_ERROR) {
 		pr_efi_err("Failed to find DRAM base\n");
+		status = EFI_LOAD_ERROR;
 		goto fail;
 	}
 
@@ -198,6 +203,7 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table_arg,
 	cmdline_ptr = efi_convert_cmdline(image, &cmdline_size, ULONG_MAX);
 	if (!cmdline_ptr) {
 		pr_efi_err("getting command line via LOADED_IMAGE_PROTOCOL\n");
+		status = EFI_OUT_OF_RESOURCES;
 		goto fail;
 	}
 
@@ -213,7 +219,7 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table_arg,
 
 	si = setup_graphics();
 
-	status = handle_kernel_image(image_addr, &image_size,
+	status = handle_kernel_image(&image_addr, &image_size,
 				     &reserve_addr,
 				     &reserve_size,
 				     dram_base, image);
@@ -260,7 +266,7 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table_arg,
 		pr_efi("Generating empty DTB\n");
 
 	if (!noinitrd()) {
-		max_addr = efi_get_max_initrd_addr(dram_base, *image_addr);
+		max_addr = efi_get_max_initrd_addr(dram_base, image_addr);
 		status = efi_load_initrd_dev_path(&initrd_addr, &initrd_size,
 						  max_addr);
 		if (status == EFI_SUCCESS) {
@@ -311,33 +317,30 @@ unsigned long efi_entry(void *handle, efi_system_table_t *sys_table_arg,
 
 	install_memreserve_table();
 
-	new_fdt_addr = fdt_addr;
 	status = allocate_new_fdt_and_exit_boot(handle,
-				&new_fdt_addr, efi_get_max_fdt_addr(dram_base),
+				&fdt_addr, efi_get_max_fdt_addr(dram_base),
 				initrd_addr, initrd_size, cmdline_ptr,
 				fdt_addr, fdt_size);
+	if (status != EFI_SUCCESS)
+		goto fail_free_initrd;
 
-	/*
-	 * If all went well, we need to return the FDT address to the
-	 * calling function so it can be passed to kernel as part of
-	 * the kernel boot protocol.
-	 */
-	if (status == EFI_SUCCESS)
-		return new_fdt_addr;
+	efi_enter_kernel(image_addr, fdt_addr);
+	/* not reached */
 
+fail_free_initrd:
 	pr_efi_err("Failed to update FDT and exit boot services\n");
 
 	efi_free(initrd_size, initrd_addr);
 	efi_free(fdt_size, fdt_addr);
 
 fail_free_image:
-	efi_free(image_size, *image_addr);
+	efi_free(image_size, image_addr);
 	efi_free(reserve_size, reserve_addr);
 fail_free_cmdline:
 	free_screen_info(si);
 	efi_free(cmdline_size, (unsigned long)cmdline_ptr);
 fail:
-	return EFI_ERROR;
+	return status;
 }
 
 /*
diff --git a/drivers/firmware/efi/libstub/arm32-stub.c b/drivers/firmware/efi/libstub/arm32-stub.c
index 7b2a6382b647..113298b8ea65 100644
--- a/drivers/firmware/efi/libstub/arm32-stub.c
+++ b/drivers/firmware/efi/libstub/arm32-stub.c
@@ -227,6 +227,7 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
 	 * Relocate the zImage, so that it appears in the lowest 128 MB
 	 * memory window.
 	 */
+	*image_addr = image->image_base;
 	*image_size = image->image_size;
 	status = efi_relocate_kernel(image_addr, *image_size, *image_size,
 				     kernel_base + MAX_UNCOMP_KERNEL_SIZE, 0, 0);
diff --git a/drivers/firmware/efi/libstub/arm64-stub.c b/drivers/firmware/efi/libstub/arm64-stub.c
index 719d03a64329..9254cd8ab2d3 100644
--- a/drivers/firmware/efi/libstub/arm64-stub.c
+++ b/drivers/firmware/efi/libstub/arm64-stub.c
@@ -43,7 +43,6 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
 {
 	efi_status_t status;
 	unsigned long kernel_size, kernel_memsize = 0;
-	void *old_image_addr = (void *)*image_addr;
 	unsigned long preferred_offset;
 	u64 phys_seed = 0;
 
@@ -141,7 +140,7 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
 		}
 		*image_addr = *reserve_addr + TEXT_OFFSET;
 	}
-	memcpy((void *)*image_addr, old_image_addr, kernel_size);
+	memcpy((void *)*image_addr, image->image_base, kernel_size);
 
 	return EFI_SUCCESS;
 }
-- 
2.17.1

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