From 380fdd7585a4c2f41b48925eba85c0654b7b858b Mon Sep 17 00:00:00 2001 From: Roland McGrath Date: Wed, 9 Jul 2008 02:39:29 -0700 Subject: [PATCH] x86 ptrace: user-sets-TF nits 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 --- arch/x86/kernel/ptrace.c | 10 ++++++++++ arch/x86/kernel/step.c | 13 +++++++++++++ include/asm-x86/thread_info.h | 2 +- 3 files changed, 24 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 34e77b16a42a..e37dccce85db 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -1416,6 +1416,16 @@ asmregparm long syscall_trace_enter(struct pt_regs *regs) { long ret = 0; + /* + * If we stepped into a sysenter/syscall insn, it trapped in + * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP. + * If user-mode had set TF itself, then it's still clear from + * do_debug() and we need to set it again to restore the user + * state. If we entered on the slow path, TF was already set. + */ + if (test_thread_flag(TIF_SINGLESTEP)) + regs->flags |= X86_EFLAGS_TF; + /* do the secure computing check first */ secure_computing(regs->orig_ax); diff --git a/arch/x86/kernel/step.c b/arch/x86/kernel/step.c index 0d2cb363ea75..e8b9863ef8c4 100644 --- a/arch/x86/kernel/step.c +++ b/arch/x86/kernel/step.c @@ -107,6 +107,19 @@ static int enable_single_step(struct task_struct *child) struct pt_regs *regs = task_pt_regs(child); unsigned long oflags; + /* + * If we stepped into a sysenter/syscall insn, it trapped in + * kernel mode; do_debug() cleared TF and set TIF_SINGLESTEP. + * If user-mode had set TF itself, then it's still clear from + * do_debug() and we need to set it again to restore the user + * state so we don't wrongly set TIF_FORCED_TF below. + * If enable_single_step() was used last and that is what + * set TIF_SINGLESTEP, then both TF and TIF_FORCED_TF are + * already set and our bookkeeping is fine. + */ + if (unlikely(test_tsk_thread_flag(child, TIF_SINGLESTEP))) + regs->flags |= X86_EFLAGS_TF; + /* * Always set TIF_SINGLESTEP - this guarantees that * we single-step system calls etc.. This will also diff --git a/include/asm-x86/thread_info.h b/include/asm-x86/thread_info.h index b2702a1eeac1..0a8f27d31d0d 100644 --- a/include/asm-x86/thread_info.h +++ b/include/asm-x86/thread_info.h @@ -118,7 +118,7 @@ struct thread_info { /* work to do in syscall_trace_enter() */ #define _TIF_WORK_SYSCALL_ENTRY \ (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU | \ - _TIF_SYSCALL_AUDIT | _TIF_SECCOMP) + _TIF_SYSCALL_AUDIT | _TIF_SECCOMP | _TIF_SINGLESTEP) /* work to do in syscall_trace_leave() */ #define _TIF_WORK_SYSCALL_EXIT \