linux-stable.git/arch/x86/kernel/step.c, branch v3.7

uprobes/x86: Do not (ab)use TIF_SINGLESTEP/user_*_single_step() for single-stepping

2012-09-15T15:37:30+00:00

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

ptrace/x86: Partly fix set_task_blockstep()->update_debugctlmsr() logic

2012-09-15T15:37:29+00:00

Afaics the usage of update_debugctlmsr() and TIF_BLOCKSTEP in
step.c was always very wrong.

1. update_debugctlmsr() was simply unneeded. The child sleeps
   TASK_TRACED, __switch_to_xtra(next_p => child) should notice
   TIF_BLOCKSTEP and set/clear DEBUGCTLMSR_BTF after resume if
   needed.

2. It is wrong. The state of DEBUGCTLMSR_BTF bit in CPU register
   should always match the state of current's TIF_BLOCKSTEP bit.

3. Even get_debugctlmsr() + update_debugctlmsr() itself does not
   look right. Irq can change other bits in MSR_IA32_DEBUGCTLMSR
   register or the caller can be preempted in between.

4. It is not safe to play with TIF_BLOCKSTEP if task != current.
   DEBUGCTLMSR_BTF and TIF_BLOCKSTEP should always match each
   other if the task is running. The tracee is stopped but it
   can be SIGKILL'ed right before set/clear_tsk_thread_flag().

However, now that uprobes uses user_enable_single_step(current)
we can't simply remove update_debugctlmsr(). So this patch adds
the additional "task == current" check and disables irqs to avoid
the race with interrupts/preemption.

Unfortunately this patch doesn't solve the last problem, we need
another fix. Probably we should teach ptrace_stop() to set/clear
single/block stepping after resume.

And afaics there is yet another problem: perf can play with
MSR_IA32_DEBUGCTLMSR from nmi, this obviously means that even
__switch_to_xtra() has problems.

Signed-off-by: Oleg Nesterov

ptrace/x86: Introduce set_task_blockstep() helper

2012-09-15T15:37:28+00:00

No functional changes, preparation for the next fix and for uprobes
single-step fixes.

Move the code playing with TIF_BLOCKSTEP/DEBUGCTLMSR_BTF into the
new helper, set_task_blockstep().

Signed-off-by: Oleg Nesterov 
Acked-by: Srikar Dronamraju

x86-64: Add user_64bit_mode paravirt op

2011-08-04T23:13:49+00:00

Three places in the kernel assume that the only long mode CPL 3
selector is __USER_CS.  This is not true on Xen -- Xen's sysretq
changes cs to the magic value 0xe033.

Two of the places are corner cases, but as of "x86-64: Improve
vsyscall emulation CS and RIP handling"
(c9712944b2a12373cb6ff8059afcfb7e826a6c54), vsyscalls will segfault
if called with Xen's extra CS selector.  This causes a panic when
older init builds die.

It seems impossible to make Xen use __USER_CS reliably without
taking a performance hit on every system call, so this fixes the
tests instead with a new paravirt op.  It's a little ugly because
ptrace.h can't include paravirt.h.

Signed-off-by: Andy Lutomirski 
Link: http://lkml.kernel.org/r/f4fcb3947340d9e96ce1054a432f183f9da9db83.1312378163.git.luto@mit.edu
Reported-by: Konrad Rzeszutek Wilk 
Signed-off-by: H. Peter Anvin

x86: Fix common misspellings

2011-03-18T09:39:30+00:00

They were generated by 'codespell' and then manually reviewed.

Signed-off-by: Lucas De Marchi 
Cc: trivial@kernel.org
LKML-Reference: <1300389856-1099-3-git-send-email-lucas.demarchi@profusion.mobi>
Signed-off-by: Ingo Molnar

x86, ptrace: Fix block-step

2010-03-26T10:33:57+00:00

Implement ptrace-block-step using TIF_BLOCKSTEP which will set
DEBUGCTLMSR_BTF when set for a task while preserving any other
DEBUGCTLMSR bits.

Signed-off-by: Peter Zijlstra 
LKML-Reference: <20100325135414.017536066@chello.nl>
Signed-off-by: Ingo Molnar

x86, perf, bts, mm: Delete the never used BTS-ptrace code

2010-03-26T10:33:55+00:00

Support for the PMU's BTS features has been upstreamed in
v2.6.32, but we still have the old and disabled ptrace-BTS,
as Linus noticed it not so long ago.

It's buggy: TIF_DEBUGCTLMSR is trampling all over that MSR without
regard for other uses (perf) and doesn't provide the flexibility
needed for perf either.

Its users are ptrace-block-step and ptrace-bts, since ptrace-bts
was never used and ptrace-block-step can be implemented using a
much simpler approach.

So axe all 3000 lines of it. That includes the *locked_memory*()
APIs in mm/mlock.c as well.

Reported-by: Linus Torvalds 
Signed-off-by: Peter Zijlstra 
Cc: Roland McGrath 
Cc: Oleg Nesterov 
Cc: Markus Metzger 
Cc: Steven Rostedt 
Cc: Andrew Morton 
LKML-Reference: <20100325135413.938004390@chello.nl>
Signed-off-by: Ingo Molnar

x86: Use get_desc_base()

2009-07-19T16:27:51+00:00

Use get_desc_base() to get the base address in desc_struct

Signed-off-by: Akinobu Mita 
LKML-Reference: <20090718150853.GA11294@localhost.localdomain>
Signed-off-by: Ingo Molnar

x86 ptrace: user-sets-TF nits

2008-07-16T19:15:17+00:00

This closes some arcane holes in single-step handling that can arise
only when user programs set TF directly (via popf or sigreturn) and
then use vDSO (syscall/sysenter) system call entry.  In those entry
paths, the clear_TF_reenable case hits and we must check TIF_SINGLESTEP
to be sure our bookkeeping stays correct wrt the user's view of TF.

Signed-off-by: Roland McGrath

x86 ptrace: block-step fix

2008-07-16T19:15:16+00:00

The enable_single_step() logic bails out early if TF is already set.
That skips some of the bookkeeping that keeps things straight.
This makes PTRACE_SINGLEBLOCK break the behavior of a user task
that was already setting TF itself in user mode.

Fix the bookkeeping to notice the old TF setting as it should.

Test case at: http://sources.redhat.com/cgi-bin/cvsweb.cgi/~checkout~/tests/ptrace-tests/tests/step-jump-cont-strict.c?cvsroot=systemtap

Signed-off-by: Roland McGrath