From 9bd1190a11c9d2c59d35cb999b8d170ad52aab5f Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Mon, 3 Sep 2012 15:24:17 +0200 Subject: 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 Acked-by: Srikar Dronamraju --- arch/x86/include/asm/processor.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'arch/x86/include/asm/processor.h') 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: -- cgit v1.2.3-70-g09d2