[PATCH 4/8] RISC-V: Filter ISA and MMU values in cpuinfo

[Palmer Dabbelt <palmer@sifive.com>]

We shouldn't be directly passing device tree values to userspace, both
because there could be mistakes in device trees and because the kernel
doesn't support arbitrary ISAs.

Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
---
 arch/riscv/kernel/cpu.c | 62 +++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 55 insertions(+), 7 deletions(-)

diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
index 19e98c1710dd..a18b4e3962a1 100644
--- a/arch/riscv/kernel/cpu.c
+++ b/arch/riscv/kernel/cpu.c
@@ -58,6 +58,57 @@ int riscv_of_processor_hartid(struct device_node *node)
 
 #ifdef CONFIG_PROC_FS
 
+static void print_isa(struct seq_file *f, const char *orig_isa)
+{
+    static const char *ext = "mafdc";
+    const char *isa = orig_isa;
+    const char *e;
+
+    /* Linux doesn't support rv32e or rv128i, and we only support booting
+     * kernels on harts with the same ISA that the kernel is compiled for. */
+#if defined(CONFIG_32BIT)
+    if (strncmp(isa, "rv32i", 5) != 0)
+        return;
+#elif defined(CONFIG_64BIT)
+    if (strncmp(isa, "rv64i", 5) != 0)
+        return;
+#endif
+
+    /* Print the base ISA, as we already know it's legal. */
+    seq_printf(f, "isa\t: ");
+    seq_write(f, isa, 5);
+    isa += 5;
+
+    /* Check the rest of the ISA string for valid extensions, printing those we
+     * find.  RISC-V ISA strings define an order, so we only print the
+     * extension bits when they're in order. */
+    for (e = ext; *e != '\0'; ++e) {
+        if (isa[0] == e[0]) {
+            seq_write(f, isa, 1);
+            isa++;
+        }
+    }
+
+    /* If we were given an unsupported ISA in the device tree then print a bit
+     * of info describing what went wrong. */
+    if (isa[0] != '\0')
+        pr_info("unsupported ISA \"%s\" in device tree", orig_isa);
+}
+
+static void print_mmu(struct seq_file *f, const char *mmu_type)
+{
+#if defined(CONFIG_32BIT)
+    if (strcmp(mmu_type, "riscv,sv32") != 0)
+        return;
+#elif defined(CONFIG_64BIT)
+    if ((strcmp(mmu_type, "riscv,sv39") != 0)
+        && (strcmp(mmu_type, "riscv,sv48") != 0))
+        return;
+#endif
+
+    seq_printf(f, "mmu\t: %s\n", mmu_type+6);
+}
+
 static void *c_start(struct seq_file *m, loff_t *pos)
 {
 	*pos = cpumask_next(*pos - 1, cpu_online_mask);
@@ -83,13 +134,10 @@ static int c_show(struct seq_file *m, void *v)
 	const char *compat, *isa, *mmu;
 
 	seq_printf(m, "hart\t: %lu\n", hart_id);
-	if (!of_property_read_string(node, "riscv,isa", &isa)
-	    && isa[0] == 'r'
-	    && isa[1] == 'v')
-		seq_printf(m, "isa\t: %s\n", isa);
-	if (!of_property_read_string(node, "mmu-type", &mmu)
-	    && !strncmp(mmu, "riscv,", 6))
-		seq_printf(m, "mmu\t: %s\n", mmu+6);
+	if (!of_property_read_string(node, "riscv,isa", &isa))
+        print_isa(m, isa);
+	if (!of_property_read_string(node, "mmu-type", &mmu))
+        print_mmu(m, mmu);
 	if (!of_property_read_string(node, "compatible", &compat)
 	    && strcmp(compat, "riscv"))
 		seq_printf(m, "uarch\t: %s\n", compat);
-- 
2.16.4