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

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Date:   Mon, 27 Aug 2018 11:42:39 -0700
From:   Palmer Dabbelt <palmer@...ive.com>
To:      linux-riscv@...ts.infradead.org
Cc:     Palmer Dabbelt <palmer@...ive.com>, aou@...s.berkeley.edu,
        daniel.lezcano@...aro.org, tglx@...utronix.de,
        jason@...edaemon.net, marc.zyngier@....com, atish.patra@....com,
        dmitriy@...-tech.org, catalin.marinas@....com,
        ard.biesheuvel@...aro.org, Greg KH <gregkh@...uxfoundation.org>,
        jeremy.linton@....com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 4/8] RISC-V: Filter ISA and MMU values in cpuinfo

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@...ive.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