efi/loongarch: Don't jump to kernel entry via the old image

Currently, the EFI entry code for LoongArch is set up to copy the
executable image to the preferred offset, but instead of branching
directly into that image, it branches to the local copy of kernel_entry,
and relies on the logic in that function to switch to the link time
address instead.

This is a bit sloppy, and not something we can support once we merge the
EFI decompressor with the EFI stub. So let's clean this up a bit, by
adding a helper that computes the offset of kernel_entry from the start
of the image, and simply adding the result to VMLINUX_LOAD_ADDRESS.

And considering that we cannot execute from anywhere else anyway, let's
avoid efi_relocate_kernel() and just allocate the pages instead.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

arch/loongarch/include/asm/efi.h

@@ -31,4 +31,6 @@ static inline unsigned long efi_get_kimg_min_align(void)
 
 #define EFI_KIMG_PREFERRED_ADDRESS	PHYSADDR(VMLINUX_LOAD_ADDRESS)
 
+unsigned long kernel_entry_address(void);
+
 #endif /* _ASM_LOONGARCH_EFI_H */

drivers/firmware/efi/libstub/loongarch-stub.c

@@ -29,18 +29,27 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
 				 efi_loaded_image_t *image,
 				 efi_handle_t image_handle)
 {
+	int nr_pages = round_up(kernel_asize, EFI_ALLOC_ALIGN) / EFI_PAGE_SIZE;
+	efi_physical_addr_t kernel_addr = EFI_KIMG_PREFERRED_ADDRESS;
 	efi_status_t status;
-	unsigned long kernel_addr = 0;
 
-	kernel_addr = (unsigned long)&kernel_offset - kernel_offset;
-
-	status = efi_relocate_kernel(&kernel_addr, kernel_fsize, kernel_asize,
-				     EFI_KIMG_PREFERRED_ADDRESS,
-				     efi_get_kimg_min_align(), 0x0);
+	/*
+	 * Allocate space for the kernel image at the preferred offset. This is
+	 * the only location in memory from where we can execute the image, so
+	 * no point in falling back to another allocation.
+	 */
+	status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
+			     EFI_LOADER_DATA, nr_pages, &kernel_addr);
+	if (status != EFI_SUCCESS)
+		return status;
 
-	*image_addr = kernel_addr;
+	*image_addr = EFI_KIMG_PREFERRED_ADDRESS;
 	*image_size = kernel_asize;
 
+	memcpy((void *)EFI_KIMG_PREFERRED_ADDRESS,
+	       (void *)&kernel_offset - kernel_offset,
+	       kernel_fsize);
+
 	return status;
 }
 
@@ -64,6 +73,13 @@ static efi_status_t exit_boot_func(struct efi_boot_memmap *map, void *priv)
 	return EFI_SUCCESS;
 }
 
+unsigned long kernel_entry_address(void)
+{
+	unsigned long base = (unsigned long)&kernel_offset - kernel_offset;
+
+	return (unsigned long)&kernel_entry - base + VMLINUX_LOAD_ADDRESS;
+}
+
 efi_status_t efi_boot_kernel(void *handle, efi_loaded_image_t *image,
 			     unsigned long kernel_addr, char *cmdline_ptr)
 {
@@ -95,8 +111,7 @@ efi_status_t efi_boot_kernel(void *handle, efi_loaded_image_t *image,
 	csr_write64(CSR_DMW0_INIT, LOONGARCH_CSR_DMWIN0);
 	csr_write64(CSR_DMW1_INIT, LOONGARCH_CSR_DMWIN1);
 
-	real_kernel_entry = (kernel_entry_t)
-		((unsigned long)&kernel_entry - kernel_addr + VMLINUX_LOAD_ADDRESS);
+	real_kernel_entry = (void *)kernel_entry_address();
 
 	real_kernel_entry(true, (unsigned long)cmdline_ptr,
 			  (unsigned long)efi_system_table);