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author | Oleg Nesterov <oleg@redhat.com> | 2012-09-03 15:24:17 +0200 |
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committer | Oleg Nesterov <oleg@redhat.com> | 2012-09-15 17:37:30 +0200 |
commit | 9bd1190a11c9d2c59d35cb999b8d170ad52aab5f (patch) | |
tree | 2a7999451f98ca752d1ea2ddd49ef4c349e18e40 | |
parent | 95cf00fa5d5e2a200a2c044c84bde8389a237e02 (diff) | |
download | linux-stable-9bd1190a11c9d2c59d35cb999b8d170ad52aab5f.tar.gz linux-stable-9bd1190a11c9d2c59d35cb999b8d170ad52aab5f.tar.bz2 linux-stable-9bd1190a11c9d2c59d35cb999b8d170ad52aab5f.zip |
uprobes/x86: Do not (ab)use TIF_SINGLESTEP/user_*_single_step() for single-stepping
user_enable/disable_single_step() was designed for ptrace, it assumes
a single user and does unnecessary and wrong things for uprobes. For
example:
- arch_uprobe_enable_step() can't trust TIF_SINGLESTEP, an
application itself can set X86_EFLAGS_TF which must be
preserved after arch_uprobe_disable_step().
- we do not want to set TIF_SINGLESTEP/TIF_FORCED_TF in
arch_uprobe_enable_step(), this only makes sense for ptrace.
- otoh we leak TIF_SINGLESTEP if arch_uprobe_disable_step()
doesn't do user_disable_single_step(), the application will
be killed after the next syscall.
- arch_uprobe_enable_step() does access_process_vm() we do
not need/want.
Change arch_uprobe_enable/disable_step() to set/clear X86_EFLAGS_TF
directly, this is much simpler and more correct. However, we need to
clear TIF_BLOCKSTEP/DEBUGCTLMSR_BTF before executing the probed insn,
add set_task_blockstep(false).
Note: with or without this patch, there is another (hopefully minor)
problem. A probed "pushf" insn can see the wrong X86_EFLAGS_TF set by
uprobes. Perhaps we should change _disable to update the stack, or
teach arch_uprobe_skip_sstep() to emulate this insn.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
-rw-r--r-- | arch/x86/include/asm/processor.h | 2 | ||||
-rw-r--r-- | arch/x86/kernel/step.c | 2 | ||||
-rw-r--r-- | arch/x86/kernel/uprobes.c | 32 |
3 files changed, 21 insertions, 15 deletions
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index d048cad9bcad..433d2e5c98a7 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -759,6 +759,8 @@ static inline void update_debugctlmsr(unsigned long debugctlmsr) wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctlmsr); } +extern void set_task_blockstep(struct task_struct *task, bool on); + /* * from system description table in BIOS. Mostly for MCA use, but * others may find it useful: diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c index f89cdc6ccd5b..cd3b2438a980 100644 --- a/arch/x86/kernel/step.c +++ b/arch/x86/kernel/step.c @@ -157,7 +157,7 @@ static int enable_single_step(struct task_struct *child) return 1; } -static void set_task_blockstep(struct task_struct *task, bool on) +void set_task_blockstep(struct task_struct *task, bool on) { unsigned long debugctl; diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c index 309a0e02b124..3b4aae68efe0 100644 --- a/arch/x86/kernel/uprobes.c +++ b/arch/x86/kernel/uprobes.c @@ -683,26 +683,30 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs) void arch_uprobe_enable_step(struct arch_uprobe *auprobe) { - struct uprobe_task *utask = current->utask; - struct arch_uprobe_task *autask = &utask->autask; + struct task_struct *task = current; + struct arch_uprobe_task *autask = &task->utask->autask; + struct pt_regs *regs = task_pt_regs(task); autask->restore_flags = 0; - if (!test_tsk_thread_flag(current, TIF_SINGLESTEP) && - !(auprobe->fixups & UPROBE_FIX_SETF)) + if (!(regs->flags & X86_EFLAGS_TF) && + !(auprobe->fixups & UPROBE_FIX_SETF)) autask->restore_flags |= UPROBE_CLEAR_TF; - /* - * The state of TIF_BLOCKSTEP is not saved. With the TF flag set we - * would to examine the opcode and the flags to make it right. Without - * TF block stepping makes no sense. - */ - user_enable_single_step(current); + + regs->flags |= X86_EFLAGS_TF; + if (test_tsk_thread_flag(task, TIF_BLOCKSTEP)) + set_task_blockstep(task, false); } void arch_uprobe_disable_step(struct arch_uprobe *auprobe) { - struct uprobe_task *utask = current->utask; - struct arch_uprobe_task *autask = &utask->autask; - + struct task_struct *task = current; + struct arch_uprobe_task *autask = &task->utask->autask; + struct pt_regs *regs = task_pt_regs(task); + /* + * The state of TIF_BLOCKSTEP was not saved so we can get an extra + * SIGTRAP if we do not clear TF. We need to examine the opcode to + * make it right. + */ if (autask->restore_flags & UPROBE_CLEAR_TF) - user_disable_single_step(current); + regs->flags &= ~X86_EFLAGS_TF; } |