riscv: Introduce virtual kernel mapping KASLR

KASLR implementation relies on a relocatable kernel so that we can move
the kernel mapping.

The seed needed to virtually move the kernel is taken from the device tree,
so we rely on the bootloader to provide a correct seed. Zkr could be used
unconditionnally instead if implemented, but that's for another patch.

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/20230722123850.634544-2-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

3 files changed, 44 insertions, 1 deletions

diff --git a/arch/riscv/kernel/pi/Makefile b/arch/riscv/kernel/pi/Makefile
index 7b593d44c712..07915dc9279e 100644
--- a/arch/riscv/kernel/pi/Makefile
+++ b/arch/riscv/kernel/pi/Makefile
@@ -35,5 +35,5 @@ $(obj)/string.o: $(srctree)/lib/string.c FORCE
 $(obj)/ctype.o: $(srctree)/lib/ctype.c FORCE
 	$(call if_changed_rule,cc_o_c)
 
-obj-y		:= cmdline_early.pi.o string.pi.o ctype.pi.o lib-fdt.pi.o lib-fdt_ro.pi.o
+obj-y		:= cmdline_early.pi.o fdt_early.pi.o string.pi.o ctype.pi.o lib-fdt.pi.o lib-fdt_ro.pi.o
 extra-y		:= $(patsubst %.pi.o,%.o,$(obj-y))
diff --git a/arch/riscv/kernel/pi/cmdline_early.c b/arch/riscv/kernel/pi/cmdline_early.c
index 05652d13c746..68e786c84c94 100644
--- a/arch/riscv/kernel/pi/cmdline_early.c
+++ b/arch/riscv/kernel/pi/cmdline_early.c
@@ -14,6 +14,7 @@ static char early_cmdline[COMMAND_LINE_SIZE];
  * LLVM complain because the function is actually unused in this file).
  */
 u64 set_satp_mode_from_cmdline(uintptr_t dtb_pa);
+bool set_nokaslr_from_cmdline(uintptr_t dtb_pa);
 
 static char *get_early_cmdline(uintptr_t dtb_pa)
 {
@@ -60,3 +61,15 @@ u64 set_satp_mode_from_cmdline(uintptr_t dtb_pa)
 
 	return match_noXlvl(cmdline);
 }
+
+static bool match_nokaslr(char *cmdline)
+{
+	return strstr(cmdline, "nokaslr");
+}
+
+bool set_nokaslr_from_cmdline(uintptr_t dtb_pa)
+{
+	char *cmdline = get_early_cmdline(dtb_pa);
+
+	return match_nokaslr(cmdline);
+}
diff --git a/arch/riscv/kernel/pi/fdt_early.c b/arch/riscv/kernel/pi/fdt_early.c
new file mode 100644
index 000000000000..899610e042ab
--- /dev/null
+++ b/arch/riscv/kernel/pi/fdt_early.c
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/types.h>
+#include <linux/init.h>
+#include <linux/libfdt.h>
+
+/*
+ * Declare the functions that are exported (but prefixed) here so that LLVM
+ * does not complain it lacks the 'static' keyword (which, if added, makes
+ * LLVM complain because the function is actually unused in this file).
+ */
+u64 get_kaslr_seed(uintptr_t dtb_pa);
+
+u64 get_kaslr_seed(uintptr_t dtb_pa)
+{
+	int node, len;
+	fdt64_t *prop;
+	u64 ret;
+
+	node = fdt_path_offset((void *)dtb_pa, "/chosen");
+	if (node < 0)
+		return 0;
+
+	prop = fdt_getprop_w((void *)dtb_pa, node, "kaslr-seed", &len);
+	if (!prop || len != sizeof(u64))
+		return 0;
+
+	ret = fdt64_to_cpu(*prop);
+	*prop = 0;
+	return ret;
+}