[riscv] Avoid potentially overwriting the scratch area during relocation

We do not currently describe the temporary page table or the temporary
stack as areas to be avoided during relocation of the iPXE image to a
new physical address.

Perform the copy of the iPXE image and zeroing of the .bss within
libprefix.S, after we have no futher use for the temporary page table
or the temporary initial stack.  Perform the copy and registration of
the system device tree in C code after relocation is complete and the
new stack (within .bss) has been set up.

This provides a clean separation of responsibilities between the
RISC-V libprefix.S and the architecture-independent fdtmem.c.  The
prefix is responsible only for relocating iPXE to the new physical
address returned from fdtmem_relocate(), and doesn't need to know or
care where fdtmem.c is planning to place the copy of the device tree.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/riscv/prefix/libprefix.S

@@ -1023,6 +1023,21 @@ install:
 	la	s6, _prefix
 	sub	s6, s5, s6
 
+	/* Copy iPXE image to new location and zero .bss */
+	mv	t0, s5
+	la	t1, _prefix
+	la	t2, _edata
+1:	LOADN	t3, (t1)
+	STOREN	t3, (t0)
+	addi	t0, t0, ( __riscv_xlen / 8 )
+	addi	t1, t1, ( __riscv_xlen / 8 )
+	blt	t1, t2, 1b
+	la	t1, _ebss
+	add	t1, t1, s6
+2:	STOREN	zero, (t0)
+	addi	t0, t0, ( __riscv_xlen / 8 )
+	blt	t0, t1, 2b
+
 	/* Jump to relocated copy */
 	la	t0, 1f
 	add	t0, t0, s6
@@ -1042,11 +1057,9 @@ install:
 	/* Store boot hart */
 	STOREN	s0, boot_hart, t0
 
-	/* Register copy of device tree as system device tree */
-	la	a0, sysfdt
-	la	a1, _end
-	li	a2, -1
-	call	fdt_parse
+	/* Copy and register system device tree */
+	phys_to_virt a0, s1
+	call	fdtmem_register
 
 	/* Return to a virtual address in the relocated copy */
 	add	ra, s2, s6

src/core/fdtmem.c

@@ -41,20 +41,15 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 /** Start address of the iPXE image */
 extern char _prefix[];
 
-/** Initialised-data size of the iPXE image (defined by linker) */
-extern size_t ABS_SYMBOL ( _filesz );
-static size_t filesz = ABS_VALUE_INIT ( _filesz );
-
-/** In-memory size of the iPXE image (defined by linker) */
-extern size_t ABS_SYMBOL ( _memsz );
-static size_t memsz = ABS_VALUE_INIT ( _memsz );
+/** End address of the iPXE image */
+extern char _end[];
 
 /** Relocation required alignment (defined by prefix or linker) */
 extern physaddr_t ABS_SYMBOL ( _max_align );
 static physaddr_t max_align = ABS_VALUE_INIT ( _max_align );
 
 /** Colour for debug messages */
-#define colour &memsz
+#define colour &_prefix[0]
 
 /** A memory region descriptor */
 struct fdtmem_region {
@@ -278,8 +273,8 @@ physaddr_t fdtmem_relocate ( struct fdt_header *hdr, size_t limit ) {
 	physaddr_t old;
 	physaddr_t new;
 	physaddr_t try;
+	size_t memsz;
 	size_t len;
-	void *dest;
 	int rc;
 
 	/* Sanity check */
@@ -297,6 +292,7 @@ physaddr_t fdtmem_relocate ( struct fdt_header *hdr, size_t limit ) {
 	}
 
 	/* Determine required length */
+	memsz = ( _end - _prefix );
 	assert ( memsz > 0 );
 	assert ( ( memsz % FDT_MAX_ALIGN ) == 0 );
 	len = ( memsz + fdt.len );
@@ -355,15 +351,39 @@ physaddr_t fdtmem_relocate ( struct fdt_header *hdr, size_t limit ) {
 			break;
 	}
 
-	/* Copy iPXE and device tree to new location */
-	if ( new != old ) {
-		dest = phys_to_virt ( new );
-		memset ( dest, 0, len );
-		memcpy ( dest, _prefix, filesz );
-		memcpy ( ( dest + memsz ), hdr, fdt.len );
-	}
-
 	DBGC ( colour, "FDTMEM relocating %#08lx => [%#08lx,%#08lx]\n",
 	       old, new, ( ( physaddr_t ) ( new + len - 1 ) ) );
 	return new;
 }
+
+/**
+ * Copy and register system device tree
+ *
+ * @v hdr		FDT header
+ * @ret rc		Return status code
+ */
+int fdtmem_register ( struct fdt_header *hdr ) {
+	struct fdt_header *copy;
+	struct fdt fdt;
+	int rc;
+
+	/* Parse FDT to obtain length */
+	if ( ( rc = fdt_parse ( &fdt, hdr, -1UL ) ) != 0 ) {
+		DBGC ( colour, "FDTMEM could not parse FDT: %s\n",
+		       strerror ( rc ) );
+		return rc;
+	}
+
+	/* Copy device tree to end of iPXE image */
+	copy = ( ( void * ) _end );
+	memcpy ( copy, hdr, fdt.len );
+
+	/* Register copy as system device tree */
+	if ( ( rc = fdt_parse ( &sysfdt, copy, -1UL ) ) != 0 ) {
+		DBGC ( colour, "FDTMEM could not register FDT: %s\n",
+		       strerror ( rc ) );
+		return rc;
+	}
+
+	return 0;
+}

src/include/ipxe/fdtmem.h

@@ -13,5 +13,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <ipxe/fdt.h>
 
 extern physaddr_t fdtmem_relocate ( struct fdt_header *hdr, size_t limit );
+extern int fdtmem_register ( struct fdt_header *hdr );
 
 #endif /* _IPXE_FDTMEM_H */