x86: single_step moved

This moves the single-step support code from ptrace_64.c into a new file
step.c, verbatim.  This paves the way for consolidating this code between
64-bit and 32-bit versions.

Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

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;
+        }
+}