x86: Extend #DF debugging aid to 64-bit

It is sometimes very helpful to be able to pinpoint the location which
causes a double fault before it turns into a triple fault and the
machine reboots. We have this for 32-bit already so extend it to 64-bit.
On 64-bit we get the register snapshot at #DF time and not from the
first exception which actually causes the #DF. It should be close
enough, though.

[ hpa: and definitely better than nothing, which is what we have now. ]

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/1368093749-31296-1-git-send-email-bp@alien8.de
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 84 insertions, 0 deletions

diff --git a/arch/x86/kernel/doublefault.c b/arch/x86/kernel/doublefault.c
new file mode 100644
index 000000000000..5d3fe8d36e4a
--- /dev/null
+++ b/arch/x86/kernel/doublefault.c
@@ -0,0 +1,84 @@
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/init.h>
+#include <linux/init_task.h>
+#include <linux/fs.h>
+
+#include <asm/uaccess.h>
+#include <asm/pgtable.h>
+#include <asm/processor.h>
+#include <asm/desc.h>
+
+#ifdef CONFIG_X86_32
+
+#define DOUBLEFAULT_STACKSIZE (1024)
+static unsigned long doublefault_stack[DOUBLEFAULT_STACKSIZE];
+#define STACK_START (unsigned long)(doublefault_stack+DOUBLEFAULT_STACKSIZE)
+
+#define ptr_ok(x) ((x) > PAGE_OFFSET && (x) < PAGE_OFFSET + MAXMEM)
+
+static void doublefault_fn(void)
+{
+        struct desc_ptr gdt_desc = {0, 0};
+        unsigned long gdt, tss;
+
+        native_store_gdt(&gdt_desc);
+        gdt = gdt_desc.address;
+
+        printk(KERN_EMERG "PANIC: double fault, gdt at %08lx [%d bytes]\n", gdt, gdt_desc.size);
+
+        if (ptr_ok(gdt)) {
+                gdt += GDT_ENTRY_TSS << 3;
+                tss = get_desc_base((struct desc_struct *)gdt);
+                printk(KERN_EMERG "double fault, tss at %08lx\n", tss);
+
+                if (ptr_ok(tss)) {
+                        struct x86_hw_tss *t = (struct x86_hw_tss *)tss;
+
+                        printk(KERN_EMERG "eip = %08lx, esp = %08lx\n",
+                               t->ip, t->sp);
+
+                        printk(KERN_EMERG "eax = %08lx, ebx = %08lx, ecx = %08lx, edx = %08lx\n",
+                                t->ax, t->bx, t->cx, t->dx);
+                        printk(KERN_EMERG "esi = %08lx, edi = %08lx\n",
+                                t->si, t->di);
+                }
+        }
+
+        for (;;)
+                cpu_relax();
+}
+
+struct tss_struct doublefault_tss __cacheline_aligned = {
+        .x86_tss = {
+                .sp0            = STACK_START,
+                .ss0            = __KERNEL_DS,
+                .ldt            = 0,
+                .io_bitmap_base = INVALID_IO_BITMAP_OFFSET,
+
+                .ip             = (unsigned long) doublefault_fn,
+                /* 0x2 bit is always set */
+                .flags          = X86_EFLAGS_SF | 0x2,
+                .sp             = STACK_START,
+                .es             = __USER_DS,
+                .cs             = __KERNEL_CS,
+                .ss             = __KERNEL_DS,
+                .ds             = __USER_DS,
+                .fs             = __KERNEL_PERCPU,
+
+                .__cr3          = __pa_nodebug(swapper_pg_dir),
+        }
+};
+
+/* dummy for do_double_fault() call */
+void df_debug(struct pt_regs *regs, long error_code) {}
+
+#else /* !CONFIG_X86_32 */
+
+void df_debug(struct pt_regs *regs, long error_code)
+{
+        pr_emerg("PANIC: double fault, error_code: 0x%lx\n", error_code);
+        show_regs(regs);
+        panic("Machine halted.");
+}
+#endif