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Commit 380fdd75 authored by Roland McGrath's avatar Roland McGrath
Browse files

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: default avatarRoland McGrath <roland@redhat.com>
parent d4d67150

arch/x86/kernel/ptrace.c

+10 −0
Original line number Diff line number Diff line
@@ -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);

arch/x86/kernel/step.c

+13 −0
Original line number Diff line number Diff line
@@ -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

include/asm-x86/thread_info.h

+1 −1
Original line number Diff line number Diff line
@@ -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	\