1 files changed, 140 insertions, 0 deletions
diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c
new file mode 100644
index 000000000000..cb3c8bc2939a
--- /dev/null
+++ b/arch/x86/kernel/step.c
@@ -0,0 +1,140 @@
+/*
+ * x86 single-step support code, common to 32-bit and 64-bit.
+ */
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/ptrace.h>
+
+#define LDT_SEGMENT 4
+
+unsigned long convert_rip_to_linear(struct task_struct *child, struct pt_regs *regs)
+{
+	unsigned long addr, seg;
+
+	addr = regs->rip;
+	seg = regs->cs & 0xffff;
+
+	/*
+	 * We'll assume that the code segments in the GDT
+	 * are all zero-based. That is largely true: the
+	 * TLS segments are used for data, and the PNPBIOS
+	 * and APM bios ones we just ignore here.
+	 */
+	if (seg & LDT_SEGMENT) {
+		u32 *desc;
+		unsigned long base;
+
+		seg &= ~7UL;
+
+		mutex_lock(&child->mm->context.lock);
+		if (unlikely((seg >> 3) >= child->mm->context.size))
+			addr = -1L; /* bogus selector, access would fault */
+		else {
+			desc = child->mm->context.ldt + seg;
+			base = ((desc[0] >> 16) |
+				((desc[1] & 0xff) << 16) |
+				(desc[1] & 0xff000000));
+
+			/* 16-bit code segment? */
+			if (!((desc[1] >> 22) & 1))
+				addr &= 0xffff;
+			addr += base;
+		}
+		mutex_unlock(&child->mm->context.lock);
+	}
+
+	return addr;
+}
+
+static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs)
+{
+	int i, copied;
+	unsigned char opcode[15];
+	unsigned long addr = convert_rip_to_linear(child, regs);
+
+	copied = access_process_vm(child, addr, opcode, sizeof(opcode), 0);
+	for (i = 0; i < copied; i++) {
+		switch (opcode[i]) {
+		/* popf and iret */
+		case 0x9d: case 0xcf:
+			return 1;
+
+			/* CHECKME: 64 65 */
+
+		/* opcode and address size prefixes */
+		case 0x66: case 0x67:
+			continue;
+		/* irrelevant prefixes (segment overrides and repeats) */
+		case 0x26: case 0x2e:
+		case 0x36: case 0x3e:
+		case 0x64: case 0x65:
+		case 0xf2: case 0xf3:
+			continue;
+
+		case 0x40 ... 0x4f:
+			if (regs->cs != __USER_CS)
+				/* 32-bit mode: register increment */
+				return 0;
+			/* 64-bit mode: REX prefix */
+			continue;
+
+			/* CHECKME: f2, f3 */
+
+		/*
+		 * pushf: NOTE! We should probably not let
+		 * the user see the TF bit being set. But
+		 * it's more pain than it's worth to avoid
+		 * it, and a debugger could emulate this
+		 * all in user space if it _really_ cares.
+		 */
+		case 0x9c:
+		default:
+			return 0;
+		}
+	}
+	return 0;
+}
+
+void user_enable_single_step(struct task_struct *child)
+{
+	struct pt_regs *regs = task_pt_regs(child);
+
+	/*
+	 * Always set TIF_SINGLESTEP - this guarantees that
+	 * we single-step system calls etc..  This will also
+	 * cause us to set TF when returning to user mode.
+	 */
+	set_tsk_thread_flag(child, TIF_SINGLESTEP);
+
+	/*
+	 * If TF was already set, don't do anything else
+	 */
+	if (regs->eflags & X86_EFLAGS_TF)
+		return;
+
+	/* Set TF on the kernel stack.. */
+	regs->eflags |= X86_EFLAGS_TF;
+
+	/*
+	 * ..but if TF is changed by the instruction we will trace,
+	 * don't mark it as being "us" that set it, so that we
+	 * won't clear it by hand later.
+	 */
+	if (is_setting_trap_flag(child, regs))
+		return;
+
+	child->ptrace |= PT_DTRACE;
+}
+
+void user_disable_single_step(struct task_struct *child)
+{
+	/* Always clear TIF_SINGLESTEP... */
+	clear_tsk_thread_flag(child, TIF_SINGLESTEP);
+
+	/* But touch TF only if it was set by us.. */
+	if (child->ptrace & PT_DTRACE) {
+		struct pt_regs *regs = task_pt_regs(child);
+		regs->eflags &= ~X86_EFLAGS_TF;
+		child->ptrace &= ~PT_DTRACE;
+	}
+}