x86: move get_segment_eip() to step.c
get_segment_eip has similarities to convert_rip_to_linear(),
and is used in a similar context. Move get_segment_eip to
step.c to allow easier consolidation.
Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
index 21ea22f..5884dd4 100644
--- a/arch/x86/kernel/step.c
+++ b/arch/x86/kernel/step.c
@@ -6,6 +6,87 @@
#include <linux/ptrace.h>
#ifdef CONFIG_X86_32
+#include <linux/uaccess.h>
+
+#include <asm/desc.h>
+
+/*
+ * Return EIP plus the CS segment base. The segment limit is also
+ * adjusted, clamped to the kernel/user address space (whichever is
+ * appropriate), and returned in *eip_limit.
+ *
+ * The segment is checked, because it might have been changed by another
+ * task between the original faulting instruction and here.
+ *
+ * If CS is no longer a valid code segment, or if EIP is beyond the
+ * limit, or if it is a kernel address when CS is not a kernel segment,
+ * then the returned value will be greater than *eip_limit.
+ *
+ * This is slow, but is very rarely executed.
+ */
+unsigned long get_segment_eip(struct pt_regs *regs,
+ unsigned long *eip_limit)
+{
+ unsigned long ip = regs->ip;
+ unsigned seg = regs->cs & 0xffff;
+ u32 seg_ar, seg_limit, base, *desc;
+
+ /* Unlikely, but must come before segment checks. */
+ if (unlikely(regs->flags & VM_MASK)) {
+ base = seg << 4;
+ *eip_limit = base + 0xffff;
+ return base + (ip & 0xffff);
+ }
+
+ /* The standard kernel/user address space limit. */
+ *eip_limit = user_mode(regs) ? USER_DS.seg : KERNEL_DS.seg;
+
+ /* By far the most common cases. */
+ if (likely(SEGMENT_IS_FLAT_CODE(seg)))
+ return ip;
+
+ /* Check the segment exists, is within the current LDT/GDT size,
+ that kernel/user (ring 0..3) has the appropriate privilege,
+ that it's a code segment, and get the limit. */
+ __asm__("larl %3,%0; lsll %3,%1"
+ : "=&r" (seg_ar), "=r" (seg_limit) : "0" (0), "rm" (seg));
+ if ((~seg_ar & 0x9800) || ip > seg_limit) {
+ *eip_limit = 0;
+ return 1; /* So that returned ip > *eip_limit. */
+ }
+
+ /* Get the GDT/LDT descriptor base.
+ When you look for races in this code remember that
+ LDT and other horrors are only used in user space. */
+ if (seg & (1<<2)) {
+ /* Must lock the LDT while reading it. */
+ mutex_lock(¤t->mm->context.lock);
+ desc = current->mm->context.ldt;
+ desc = (void *)desc + (seg & ~7);
+ } else {
+ /* Must disable preemption while reading the GDT. */
+ desc = (u32 *)get_cpu_gdt_table(get_cpu());
+ desc = (void *)desc + (seg & ~7);
+ }
+
+ /* Decode the code segment base from the descriptor */
+ base = get_desc_base((struct desc_struct *)desc);
+
+ if (seg & (1<<2))
+ mutex_unlock(¤t->mm->context.lock);
+ else
+ put_cpu();
+
+ /* Adjust EIP and segment limit, and clamp at the kernel limit.
+ It's legitimate for segments to wrap at 0xffffffff. */
+ seg_limit += base;
+ if (seg_limit < *eip_limit && seg_limit >= base)
+ *eip_limit = seg_limit;
+ return ip + base;
+}
+#endif
+
+#ifdef CONFIG_X86_32
static
#endif
unsigned long convert_rip_to_linear(struct task_struct *child, struct pt_regs *regs)