Messages in this thread Patch in this message | | | From | Roland McGrath <> | Subject | [PATCH 1/4] x86 ptrace: block-step fix | Date | Wed, 16 Jul 2008 16:03:16 -0700 (PDT) |
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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 <roland@redhat.com> --- arch/x86/kernel/step.c | 22 ++++++++++++++++------ 1 files changed, 16 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c index 92c20fe..0d2cb36 100644 --- a/arch/x86/kernel/step.c +++ b/arch/x86/kernel/step.c @@ -105,6 +105,7 @@ static int is_setting_trap_flag(struct task_struct *child, struct pt_regs *regs) static int enable_single_step(struct task_struct *child) { struct pt_regs *regs = task_pt_regs(child); + unsigned long oflags; /* * Always set TIF_SINGLESTEP - this guarantees that @@ -113,11 +114,7 @@ static int enable_single_step(struct task_struct *child) */ set_tsk_thread_flag(child, TIF_SINGLESTEP); - /* - * If TF was already set, don't do anything else - */ - if (regs->flags & X86_EFLAGS_TF) - return 0; + oflags = regs->flags; /* Set TF on the kernel stack.. */ regs->flags |= X86_EFLAGS_TF; @@ -126,9 +123,22 @@ static int enable_single_step(struct task_struct *child) * ..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)) + 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);
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