[PATCH v2 3/3] RISC-V: Use Zkr to seed KASLR base address

[Jesse Taube]

Parse the device tree for Zkr in isa string.
If Zkr is present, use it to seed the kernel base address.

Signed-off-by: Jesse Taube <jesse at rivosinc.com>
---
 arch/riscv/kernel/pi/Makefile           |  2 +-
 arch/riscv/kernel/pi/archrandom_early.c | 30 ++++++++
 arch/riscv/kernel/pi/fdt_early.c        | 94 +++++++++++++++++++++++++
 arch/riscv/kernel/pi/pi.h               |  3 +
 arch/riscv/mm/init.c                    |  5 +-
 5 files changed, 132 insertions(+), 2 deletions(-)
 create mode 100644 arch/riscv/kernel/pi/archrandom_early.c

diff --git a/arch/riscv/kernel/pi/Makefile b/arch/riscv/kernel/pi/Makefile
index 1ef7584be0c3..dba902f2a538 100644
--- a/arch/riscv/kernel/pi/Makefile
+++ b/arch/riscv/kernel/pi/Makefile
@@ -33,5 +33,5 @@ $(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 fdt_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 archrandom_early.pi.o
 extra-y		:= $(patsubst %.pi.o,%.o,$(obj-y))
diff --git a/arch/riscv/kernel/pi/archrandom_early.c b/arch/riscv/kernel/pi/archrandom_early.c
new file mode 100644
index 000000000000..c6261165e8a6
--- /dev/null
+++ b/arch/riscv/kernel/pi/archrandom_early.c
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <asm/csr.h>
+#include <linux/processor.h>
+
+#include "pi.h"
+
+/*
+ * To avoid rewriting code include asm/archrandom.h and create macros
+ * for the functions that won't be included.
+ */
+#undef riscv_has_extension_unlikely
+#define riscv_has_extension_likely(...) false
+#undef pr_err_once
+#define pr_err_once(...)
+
+#include <asm/archrandom.h>
+
+u64 get_kaslr_seed_zkr(const uintptr_t dtb_pa)
+{
+	unsigned long seed = 0;
+
+	if (!early_isa_str((const void *)dtb_pa, "zkr"))
+		return 0;
+
+	if (!csr_seed_long(&seed))
+		return 0;
+
+	return seed;
+}
diff --git a/arch/riscv/kernel/pi/fdt_early.c b/arch/riscv/kernel/pi/fdt_early.c
index 40ee299702bf..ba76197b44d1 100644
--- a/arch/riscv/kernel/pi/fdt_early.c
+++ b/arch/riscv/kernel/pi/fdt_early.c
@@ -23,3 +23,97 @@ u64 get_kaslr_seed(uintptr_t dtb_pa)
 	*prop = 0;
 	return ret;
 }
+
+/* Based off of fdt_stringlist_contains */
+static int isa_string_contains(const char *strlist, int listlen, const char *str)
+{
+	int len = strlen(str);
+	const char *p;
+
+	while (listlen >= len) {
+		if (strncasecmp(str, strlist, len) == 0)
+			return 1;
+		p = memchr(strlist, '_', listlen);
+		if (!p)
+			p = memchr(strlist, '\0', listlen);
+		if (!p)
+			return 0; /* malformed strlist.. */
+		listlen -= (p - strlist) + 1;
+		strlist = p + 1;
+	}
+
+	return 0;
+}
+
+/* Based off of fdt_nodename_eq_ */
+static int fdt_node_name_eq(const void *fdt, int offset,
+			    const char *s)
+{
+	int olen;
+	int len = strlen(s);
+	const char *p = fdt_get_name(fdt, offset, &olen);
+
+	if (!p || olen < len)
+		/* short match */
+		return 0;
+
+	if (memcmp(p, s, len) != 0)
+		return 0;
+
+	if (p[len] == '\0')
+		return 1;
+	else if (!memchr(s, '@', len) && (p[len] == '@'))
+		return 1;
+	else
+		return 0;
+}
+
+/*
+ * Returns true if the extension is in the isa string
+ * Returns false if the extension is not found
+ */
+static bool get_ext_named(const void *fdt, int node, const char *name)
+{
+	const void *prop;
+	int len;
+
+	prop = fdt_getprop(fdt, node, "riscv,isa-base", &len);
+	if (prop && isa_string_contains(prop, len, name))
+		return true;
+
+	prop = fdt_getprop(fdt, node, "riscv,isa-extensions", &len);
+	if (prop && isa_string_contains(prop, len, name))
+		return true;
+
+	prop = fdt_getprop(fdt, node, "riscv,isa", &len);
+	if (prop && isa_string_contains(prop, len, name))
+		return true;
+
+	return false;
+}
+
+/*
+ * Returns true if the extension is in the isa string on all cpus
+ * Returns false if the extension is not found
+ */
+bool early_isa_str(const void *fdt, const char *ext_name)
+{
+	int node, parent;
+	bool ret = false;
+
+	parent = fdt_path_offset(fdt, "/cpus");
+	if (parent < 0)
+		return false;
+
+	fdt_for_each_subnode(node, fdt, parent) {
+		if (!fdt_node_name_eq(fdt, node, "cpu"))
+			continue;
+
+		if (!get_ext_named(fdt, node, ext_name))
+			return false;
+
+		ret = true;
+	}
+
+	return ret;
+}
diff --git a/arch/riscv/kernel/pi/pi.h b/arch/riscv/kernel/pi/pi.h
index 65da99466baf..26e7e5f84a30 100644
--- a/arch/riscv/kernel/pi/pi.h
+++ b/arch/riscv/kernel/pi/pi.h
@@ -4,6 +4,8 @@
 
 #include <linux/types.h>
 
+bool early_isa_str(const void *fdt, const char *ext_name);
+
 /*
  * The folowing functions are exported (but prefixed) declare them here so
  * that LLVM does not complain it lacks the 'static' keyword (which, if
@@ -11,6 +13,7 @@
  */
 
 u64 get_kaslr_seed(uintptr_t dtb_pa);
+u64 get_kaslr_seed_zkr(const uintptr_t dtb_pa);
 bool set_nokaslr_from_cmdline(uintptr_t dtb_pa);
 u64 set_satp_mode_from_cmdline(uintptr_t dtb_pa);
 
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 9940171c79f0..bfb068dc4a64 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -1025,6 +1025,7 @@ static void __init pt_ops_set_late(void)
 #ifdef CONFIG_RANDOMIZE_BASE
 extern bool __init __pi_set_nokaslr_from_cmdline(uintptr_t dtb_pa);
 extern u64 __init __pi_get_kaslr_seed(uintptr_t dtb_pa);
+extern u64 __init __pi_get_kaslr_seed_zkr(const uintptr_t dtb_pa);
 
 static int __init print_nokaslr(char *p)
 {
@@ -1045,10 +1046,12 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 
 #ifdef CONFIG_RANDOMIZE_BASE
 	if (!__pi_set_nokaslr_from_cmdline(dtb_pa)) {
-		u64 kaslr_seed = __pi_get_kaslr_seed(dtb_pa);
+		u64 kaslr_seed = __pi_get_kaslr_seed_zkr(dtb_pa);
 		u32 kernel_size = (uintptr_t)(&_end) - (uintptr_t)(&_start);
 		u32 nr_pos;
 
+		if (kaslr_seed == 0)
+			kaslr_seed = __pi_get_kaslr_seed(dtb_pa);
 		/*
 		 * Compute the number of positions available: we are limited
 		 * by the early page table that only has one PUD and we must
-- 
2.45.2