Release 4.14 arch/x86/kernel/step.c
// SPDX-License-Identifier: GPL-2.0
/*
* x86 single-step support code, common to 32-bit and 64-bit.
*/
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/mm.h>
#include <linux/ptrace.h>
#include <asm/desc.h>
#include <asm/mmu_context.h>
unsigned long convert_ip_to_linear(struct task_struct *child, struct pt_regs *regs)
{
unsigned long addr, seg;
addr = regs->ip;
seg = regs->cs;
if (v8086_mode(regs)) {
addr = (addr & 0xffff) + (seg << 4);
return addr;
}
#ifdef CONFIG_MODIFY_LDT_SYSCALL
/*
* 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 & SEGMENT_TI_MASK) == SEGMENT_LDT) {
struct desc_struct *desc;
unsigned long base;
seg >>= 3;
mutex_lock(&child->mm->context.lock);
if (unlikely(!child->mm->context.ldt ||
seg >= child->mm->context.ldt->nr_entries))
addr = -1L; /* bogus selector, access would fault */
else {
desc = &child->mm->context.ldt->entries[seg];
base = get_desc_base(desc);
/* 16-bit code segment? */
if (!desc->d)
addr &= 0xffff;
addr += base;
}
mutex_unlock(&child->mm->context.lock);
}
#endif
return addr;
}
Contributors
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| Andrew Lutomirski | 21 | 10.94% | 2 | 20.00% |
| Akinobu Mita | 7 | 3.65% | 1 | 10.00% |
| H. Peter Anvin | 4 | 2.08% | 1 | 10.00% |
| Juergen Gross | 2 | 1.04% | 1 | 10.00% |
| Harvey Harrison | 1 | 0.52% | 1 | 10.00% |
| Borislav Petkov | 1 | 0.52% | 1 | 10.00% |
| Total | 192 | 100.00% | 10 | 100.00% |
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_ip_to_linear(child, regs);
copied = access_process_vm(child, addr, opcode, sizeof(opcode),
FOLL_FORCE);
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 0xf0: case 0xf2: case 0xf3:
continue;
#ifdef CONFIG_X86_64
case 0x40 ... 0x4f:
if (!user_64bit_mode(regs))
/* 32-bit mode: register increment */
return 0;
/* 64-bit mode: REX prefix */
continue;
#endif
/* 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;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Roland McGrath | 159 | 96.36% | 3 | 50.00% |
| Andrew Lutomirski | 4 | 2.42% | 1 | 16.67% |
| Lorenzo Stoakes | 1 | 0.61% | 1 | 16.67% |
| Harvey Harrison | 1 | 0.61% | 1 | 16.67% |
| Total | 165 | 100.00% | 6 | 100.00% |
/*
* Enable single-stepping. Return nonzero if user mode is not using TF itself.
*/
static int enable_single_step(struct task_struct *child)
{
struct pt_regs *regs = task_pt_regs(child);
unsigned long oflags;
/*
* If we stepped into a sysenter/syscall insn, it trapped in
* kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP.
* If user-mode had set TF itself, then it's still clear from
* do_debug() and we need to set it again to restore the user
* state so we don't wrongly set TIF_FORCED_TF below.
* If enable_single_step() was used last and that is what
* set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are
* already set and our bookkeeping is fine.
*/
if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP)))
regs->flags |= X86_EFLAGS_TF;
/*
* 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);
oflags = regs->flags;
/* Set TF on the kernel stack.. */
regs->flags |= 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.
*
* Note that if we don't actually execute the popf because
* of a signal arriving right now or suchlike, we will lose
* track of the fact that it really was "us" that set it.
*/
if (is_setting_trap_flag(child, regs)) {
clear_tsk_thread_flag(child, TIF_FORCED_TF);
return 0;
}
/*
* If TF was already set, check whether it was us who set it.
* If not, we should never attempt a block step.
*/
if (oflags & X86_EFLAGS_TF)
return test_tsk_thread_flag(child, TIF_FORCED_TF);
set_tsk_thread_flag(child, TIF_FORCED_TF);
return 1;
}
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| Person | Tokens | Prop | Commits | CommitProp |
| Roland McGrath | 110 | 98.21% | 5 | 83.33% |
| H. Peter Anvin | 2 | 1.79% | 1 | 16.67% |
| Total | 112 | 100.00% | 6 | 100.00% |
void set_task_blockstep(struct task_struct *task, bool on)
{
unsigned long debugctl;
/*
* Ensure irq/preemption can't change debugctl in between.
* Note also that both TIF_BLOCKSTEP and debugctl should
* be changed atomically wrt preemption.
*
* NOTE: this means that set/clear TIF_BLOCKSTEP is only safe if
* task is current or it can't be running, otherwise we can race
* with __switch_to_xtra(). We rely on ptrace_freeze_traced() but
* PTRACE_KILL is not safe.
*/
local_irq_disable();
debugctl = get_debugctlmsr();
if (on) {
debugctl |= DEBUGCTLMSR_BTF;
set_tsk_thread_flag(task, TIF_BLOCKSTEP);
} else {
debugctl &= ~DEBUGCTLMSR_BTF;
clear_tsk_thread_flag(task, TIF_BLOCKSTEP);
}
if (task == current)
update_debugctlmsr(debugctl);
local_irq_enable();
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Oleg Nesterov | 72 | 100.00% | 3 | 100.00% |
| Total | 72 | 100.00% | 3 | 100.00% |
/*
* Enable single or block step.
*/
static void enable_step(struct task_struct *child, bool block)
{
/*
* Make sure block stepping (BTF) is not enabled unless it should be.
* Note that we don't try to worry about any is_setting_trap_flag()
* instructions after the first when using block stepping.
* So no one should try to use debugger block stepping in a program
* that uses user-mode single stepping itself.
*/
if (enable_single_step(child) && block)
set_task_blockstep(child, true);
else if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
set_task_blockstep(child, false);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Peter Zijlstra | 23 | 47.92% | 1 | 25.00% |
| Roland McGrath | 20 | 41.67% | 1 | 25.00% |
| Oleg Nesterov | 4 | 8.33% | 1 | 25.00% |
| Lucas De Marchi | 1 | 2.08% | 1 | 25.00% |
| Total | 48 | 100.00% | 4 | 100.00% |
void user_enable_single_step(struct task_struct *child)
{
enable_step(child, 0);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Roland McGrath | 17 | 100.00% | 1 | 100.00% |
| Total | 17 | 100.00% | 1 | 100.00% |
void user_enable_block_step(struct task_struct *child)
{
enable_step(child, 1);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Roland McGrath | 17 | 100.00% | 2 | 100.00% |
| Total | 17 | 100.00% | 2 | 100.00% |
void user_disable_single_step(struct task_struct *child)
{
/*
* Make sure block stepping (BTF) is disabled.
*/
if (test_tsk_thread_flag(child, TIF_BLOCKSTEP))
set_task_blockstep(child, false);
/* Always clear TIF_SINGLESTEP... */
clear_tsk_thread_flag(child, TIF_SINGLESTEP);
/* But touch TF only if it was set by us.. */
if (test_and_clear_tsk_thread_flag(child, TIF_FORCED_TF))
task_pt_regs(child)->flags &= ~X86_EFLAGS_TF;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Roland McGrath | 38 | 69.09% | 3 | 50.00% |
| Peter Zijlstra | 14 | 25.45% | 1 | 16.67% |
| Oleg Nesterov | 2 | 3.64% | 1 | 16.67% |
| H. Peter Anvin | 1 | 1.82% | 1 | 16.67% |
| Total | 55 | 100.00% | 6 | 100.00% |
Overall Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Roland McGrath | 529 | 75.57% | 8 | 33.33% |
| Oleg Nesterov | 78 | 11.14% | 3 | 12.50% |
| Peter Zijlstra | 37 | 5.29% | 1 | 4.17% |
| Andrew Lutomirski | 28 | 4.00% | 3 | 12.50% |
| Akinobu Mita | 10 | 1.43% | 1 | 4.17% |
| H. Peter Anvin | 7 | 1.00% | 1 | 4.17% |
| Ingo Molnar | 3 | 0.43% | 1 | 4.17% |
| Juergen Gross | 2 | 0.29% | 1 | 4.17% |
| Harvey Harrison | 2 | 0.29% | 1 | 4.17% |
| Greg Kroah-Hartman | 1 | 0.14% | 1 | 4.17% |
| Lorenzo Stoakes | 1 | 0.14% | 1 | 4.17% |
| Lucas De Marchi | 1 | 0.14% | 1 | 4.17% |
| Borislav Petkov | 1 | 0.14% | 1 | 4.17% |
| Total | 700 | 100.00% | 24 | 100.00% |
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