riscv: libstub: Implement KASLR by using generic functions

We can now use arm64 functions to handle the move of the kernel physical
mapping: if KASLR is enabled, we will try to get a random seed from the
firmware, if not possible, the kernel will be moved to a location that
suits its alignment constraints.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Tested-by: Conor Dooley <conor.dooley@microchip.com>
Tested-by: Song Shuai <songshuaishuai@tinylab.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://lore.kernel.org/r/20230722123850.634544-6-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/efi.h

@@ -51,4 +51,6 @@ void efi_virtmap_unload(void);
 
 unsigned long stext_offset(void);
 
+void efi_icache_sync(unsigned long start, unsigned long end);
+
 #endif /* _ASM_EFI_H */

arch/riscv/kernel/image-vars.h

@@ -27,6 +27,7 @@ __efistub__start		= _start;
 __efistub__start_kernel		= _start_kernel;
 __efistub__end			= _end;
 __efistub__edata		= _edata;
+__efistub___init_text_end	= __init_text_end;
 __efistub_screen_info		= screen_info;
 
 #endif

drivers/firmware/efi/libstub/Makefile

@@ -88,7 +88,7 @@ lib-$(CONFIG_EFI_GENERIC_STUB)	+= efi-stub.o string.o intrinsics.o systable.o \
 lib-$(CONFIG_ARM)		+= arm32-stub.o
 lib-$(CONFIG_ARM64)		+= kaslr.o arm64.o arm64-stub.o smbios.o
 lib-$(CONFIG_X86)		+= x86-stub.o
-lib-$(CONFIG_RISCV)		+= riscv.o riscv-stub.o
+lib-$(CONFIG_RISCV)		+= kaslr.o riscv.o riscv-stub.o
 lib-$(CONFIG_LOONGARCH)		+= loongarch.o loongarch-stub.o
 
 CFLAGS_arm32-stub.o		:= -DTEXT_OFFSET=$(TEXT_OFFSET)

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

@@ -30,32 +30,29 @@ efi_status_t handle_kernel_image(unsigned long *image_addr,
 				 efi_loaded_image_t *image,
 				 efi_handle_t image_handle)
 {
-	unsigned long kernel_size = 0;
-	unsigned long preferred_addr;
+	unsigned long kernel_size, kernel_codesize, kernel_memsize;
 	efi_status_t status;
 
 	kernel_size = _edata - _start;
+	kernel_codesize = __init_text_end - _start;
+	kernel_memsize = kernel_size + (_end - _edata);
 	*image_addr = (unsigned long)_start;
-	*image_size = kernel_size + (_end - _edata);
-
-	/*
-	 * RISC-V kernel maps PAGE_OFFSET virtual address to the same physical
-	 * address where kernel is booted. That's why kernel should boot from
-	 * as low as possible to avoid wastage of memory. Currently, dram_base
-	 * is occupied by the firmware. So the preferred address for kernel to
-	 * boot is next aligned address. If preferred address is not available,
-	 * relocate_kernel will fall back to efi_low_alloc_above to allocate
-	 * lowest possible memory region as long as the address and size meets
-	 * the alignment constraints.
-	 */
-	preferred_addr = EFI_KIMG_PREFERRED_ADDRESS;
-	status = efi_relocate_kernel(image_addr, kernel_size, *image_size,
-				     preferred_addr, efi_get_kimg_min_align(),
-				     0x0);
+	*image_size = kernel_memsize;
+	*reserve_size = *image_size;
 
+	status = efi_kaslr_relocate_kernel(image_addr,
+					   reserve_addr, reserve_size,
+					   kernel_size, kernel_codesize, kernel_memsize,
+					   efi_kaslr_get_phys_seed(image_handle));
 	if (status != EFI_SUCCESS) {
 		efi_err("Failed to relocate kernel\n");
 		*image_size = 0;
 	}
+
 	return status;
 }
+
+void efi_icache_sync(unsigned long start, unsigned long end)
+{
+	asm volatile ("fence.i" ::: "memory");
+}