From: Oleg Nesterov <oleg@redhat.com>
To: Ingo Molnar <mingo@elte.hu>,
Peter Zijlstra <peterz@infradead.org>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
Anton Arapov <anton@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Roland McGrath <roland@hack.frob.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: [PATCH 5/7] uprobes: Do not (ab)use TIF_SINGLESTEP/user_*_single_step() for single-stepping
Date: Mon, 3 Sep 2012 17:26:13 +0200 [thread overview]
Message-ID: <20120903152613.GA9078@redhat.com> (raw)
In-Reply-To: <20120903152525.GA9028@redhat.com>
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>
---
arch/x86/include/asm/processor.h | 2 ++
arch/x86/kernel/step.c | 2 +-
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 d048cad..433d2e5 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 f89cdc6..cd3b243 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 309a0e0..3b4aae6 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;
}
--
1.5.5.1
next prev parent reply other threads:[~2012-09-03 15:24 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-03 15:25 [PATCH 0/7] uprobes: single-step fixes Oleg Nesterov
2012-09-03 15:25 ` [PATCH 1/7] uprobes: Introduce arch_uprobe_enable/disable_step() Oleg Nesterov
2012-09-07 14:57 ` Srikar Dronamraju
2012-09-03 15:26 ` [PATCH 2/7] uprobes: x86: Implement x86 specific arch_uprobe_*_step Oleg Nesterov
2012-09-07 14:59 ` Srikar Dronamraju
2012-09-03 15:26 ` [PATCH 3/7] ptrace: Introduce set_task_blockstep() helper Oleg Nesterov
2012-09-07 15:00 ` Srikar Dronamraju
2012-09-03 15:26 ` [PATCH 4/7] ptrace: Partly fix set_task_blockstep()->update_debugctlmsr() logic Oleg Nesterov
2012-09-07 15:14 ` Srikar Dronamraju
2012-09-10 16:57 ` Sebastian Andrzej Siewior
2012-09-10 17:45 ` Peter Zijlstra
2012-09-10 17:27 ` Oleg Nesterov
2012-09-03 15:26 ` Oleg Nesterov [this message]
2012-09-07 15:11 ` [PATCH 5/7] uprobes: Do not (ab)use TIF_SINGLESTEP/user_*_single_step() for single-stepping Srikar Dronamraju
2012-09-07 15:50 ` Oleg Nesterov
2012-09-08 7:49 ` Srikar Dronamraju
2012-09-03 15:26 ` [PATCH 6/7] uprobes: Xol should send SIGTRAP if X86_EFLAGS_TF was set Oleg Nesterov
2012-09-12 12:08 ` Srikar Dronamraju
2012-09-12 14:45 ` Oleg Nesterov
2012-09-03 15:26 ` [PATCH 7/7] uprobes: Make arch_uprobe_task->saved_trap_nr "unsigned int" Oleg Nesterov
2012-09-12 12:27 ` Srikar Dronamraju
2012-09-08 17:06 ` [PATCH 0/7] uprobes: single-step fixes Oleg Nesterov
2012-09-12 12:33 ` Srikar Dronamraju
2012-09-08 17:06 ` [PATCH 8/7] uprobes: Fix arch_uprobe_disable_step() && UTASK_SSTEP_TRAPPED interaction Oleg Nesterov
2012-09-12 12:36 ` Srikar Dronamraju
2012-09-10 16:57 ` [PATCH 0/7] uprobes: single-step fixes Sebastian Andrzej Siewior
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